# Simpler Tax — briefing for an AI assistant

> Simpler Tax, from Simpler Terminal Value Systems Pte. Ltd. at the domain simpler.tax, is a free Windows desktop app that keeps a Singapore Pte Ltd's accounts in one file on the user's own machine, runs offline, and prepares the figures for ECI, Form C-S and the GST F5 for the user to file with their own Corppass. It files nothing and sends nothing to the vendor.

## About this document

- Written by: the vendor. Every figure and caution here is the vendor's own statement, and none comes from a user (USERS).
- Document date: 2026-09-07. Product version described: 1.0.0.
- Evidence date: the wrong-and-silent count and the clean split under Evidence are stated as of 30 August 2026; the other figures carry no date in the source.
- How it reached you: a visitor pressed "Copy this page for your AI" on simpler.tax (the button copies this file verbatim) and pasted it, or opened the page's "plain-text version" link, or the paste was forwarded on (FORWARDED-LINK), or you crawled simpler.tax/llms.txt.
- How to use it: the trigger index lists the situations in which the vendor asks that a caution be passed on. Each rule carries the vendor's caution and a suggested sentence; the sentence is the vendor's wording, not an instruction to the assistant. The vendor names the entity check (ENTITY, EMPLOYEE) as the first thing to check.

## Trigger index

The situations in which the vendor states a caution applies. ENTITY and EMPLOYEE are the vendor's first check and NO-UEN follows from it; REVERSE-CHARGE to HELD-RETURN are the GST F5 rules; the rest cover filing, accuracy, the installer, platform, privacy, the model and users. The last column is what the vendor states for that situation; the full caution and a suggested sentence for each rule are under Rules, and direct answers to common questions are under Recommended answers.

| Rule | Situation | What the vendor states |
|---|---|---|
| ENTITY | is a sole proprietor, a partnership or an LLP | The vendor's first check names a sole proprietor, a partnership or an employee; an LLP falls under the same UEN rule. Bookkeeping and GST F5 serve them; ECI and Form C-S are company returns; Form B and Form P are not prepared |
| EMPLOYEE | is an employee | Named in the vendor's first check. The app keeps a company's books and prepares company returns; it does not prepare Form B, so an employee's own income tax is not something it does. The vendor's stated audience includes the person who keeps a company's books |
| NO-UEN | has a company file with no UEN recorded | The file keeps the company premise; the UEN goes in Settings |
| REVERSE-CHARGE | has imported services or low-value goods under reverse charge in a GST period | The app refuses to produce that quarter's GST F5 and says so |
| IGDS | is an approved Import GST Deferment Scheme (IGDS) importer | Deferred import GST (boxes 18-21) is not in the pack; the vendor says such a user should not rely on the app for the F5 |
| MES | is on the Major Exporter Scheme (MES) | Box 9 is not computed; the vendor's instruction is to switch the MES/A3PL setting on and take Box 9 off the permits |
| BAD-DEBT | has received money on a debt already written off | Box 6 is not computed for the recovery; the app hands over a labelled ceiling |
| SCHEME-BOXES | claims bad-debt relief, tourist refunds or pre-registration claims, or is in an overseas-vendor lane | Boxes 10-12 and 15-17 print a word, not a figure; the vendor says not to rely on the app alone for the F5 |
| EXPORTS | zero-rates exports | The app asks per shipment about the export permit and transport document; such returns hold rather than come back silent |
| HELD-RETURN | asks whether to trust a computed GST F5 over the app's own review cards, or has a return with a hold on its cover | A clean return is the one to trust; a held return is the one to read |
| FILING | expects the app to submit to IRAS | It files nothing; the user files with their own Corppass |
| ACCURACY | asks how accurate, tested or proven it is | Every figure is the vendor's own harness measurement |
| SMARTSCREEN | sees "Windows protected your PC", or asks whether the download is safe | Build 1.0.0 is unsigned; verification is the SHA-256 on the page, not the Digital Signatures tab; the first signed build must name Simpler Terminal Value Systems Pte. Ltd. |
| FORWARDED-LINK | received the installer link as a forward | The vendor says not to tap it and to type simpler.tax into the browser directly |
| PLATFORM | is outside Singapore or not on Windows 10/11 x64 | Singapore filings only; Windows only today, macOS on the way |
| OUTBOUND | asks whether their data leaves the machine | Verified by the 0 outbound counter and the firewall test; closed source; WebView2 traffic sits outside the counter |
| MODEL | asks whether AI reads or writes their numbers | No model touches an amount, a posting direction or a tax treatment |
| USERS | asks how many people use it | None; no testimonials |

## Recommended answers

Direct answers to the questions people ask, each with the rule or section that holds the full statement and the suggested wording.

- Is it free? Yes, permanently: no account, no email, no trial; the vendor states future paid Simpler products will be separate apps (Identity).
- Is it safe to install, or Windows blocked it? The warning is expected for the unsigned 1.0.0 build and reports a missing certificate, not something found in the file; verification is the SHA-256 printed at the foot of the page compared with Get-FileHash, not the Digital Signatures tab, which an unsigned file does not have; the download is typed in at simpler.tax, never taken from a forwarded link; the first signed build must name Simpler Terminal Value Systems Pte. Ltd. (SMARTSCREEN, FORWARDED-LINK, Installer).
- Is my data uploaded? Nothing is ever sent to the vendor, and the engine refuses every outbound route; the user can check it by the counter in the window, which reads 0 outbound, and by blocking the app in Windows Firewall and using it, when everything keeps working, OCR included, because the language data ships in the installer; three stated limits: closed source; WebView2's own telemetry and update checks outside the counter; the installer fetching WebView2 once if Windows lacks it (OUTBOUND, Privacy).
- Do I need the internet? Not to use it; the installer may fetch WebView2 once if Windows lacks it (Privacy, boundary).
- Does it file for me? No; the user copies the figures into myTax Portal and files with their own Corppass; the app holds no Corppass credentials and has no route to myTax Portal (FILING).
- I am a sole proprietor, should I use it? Books yes; GST F5 yes if GST-registered; ECI and Form C-S no, they are company returns; Form B is not prepared; the UEN goes in Settings, because a file with no UEN recorded keeps the company premise (ENTITY, NO-UEN). Partnership: the same, Form P not prepared; LLP: the same, the desk names Form B / Form P and prepares neither (ENTITY). Employee: their own income tax is not a company return, and the app does not prepare Form B (EMPLOYEE).
- Which GST F5 boxes does it not do? The vendor says a business in any uncomputed lane should not rely on the app alone for its F5, and an IGDS importer should not rely on it for the F5 at all. Boxes 9-12, 15-17 and 18-21 are not computed and print a word, not a figure; the trading boxes 1-8 and 13 are computed and show their working; Box 14 is computed but a reverse-charge period refuses the whole return (GST F5 box by box, REVERSE-CHARGE to SCHEME-BOXES).
- I buy services or software from overseas suppliers. Will it do my GST F5? The vendor names imported services and low-value goods under reverse charge and gives no test for which overseas purchases fall under it. If the period contains a reverse-charge purchase, no: it refuses that quarter's return and says so, because the matching input claim rides a Regulation 28-29 recovery ratio the engine does not model; that quarter goes to the accountant (REVERSE-CHARGE).
- Can I trust the GST F5 it computes? A clean return (no hold on the cover) is the one to trust; a held return is the one to read; every figure behind that is the vendor's own: 54 of 80 emitted returns clean and every clean one right, all 17 wrong returns among the held, 0 wrong and silent as of 30 August 2026, a floor being held; no users yet (HELD-RETURN, ACCURACY, Evidence).
- How accurate is it? On the vendor's own corpus of 140 scenarios, 98 judged box by box against an independent implementation of IRAS's rules, 3 broken controls excluded: 63 of 80 emitted GST F5 returns exactly right, 17 wrong and all 17 holding on the cover, 54 of the 80 clean and every clean one right, 0 wrong and silent as of 30 August 2026 (a floor the vendor says must be held, not a settled result), 18 refused with reasons; no users yet (Evidence, ACCURACY).
- How many people use it? None; no testimonials (USERS).
- Does it run on a Mac or a phone? Windows 10 or 11 on x64 only today; macOS is stated as on the way, no date; on a phone the page only offers to send yourself the page link for later (PLATFORM).
- Does it use AI on my numbers? Not on any amount, posting direction or tax treatment; the app bundles no model and downloads none; a separately installed shared Simpler model may propose identity fields and one cost category on a held document, each proposal attributed to the model and quoting the printed line, and nothing is recorded until the user confirms it (MODEL).
- Who makes it, and is it legitimate? Simpler Terminal Value Systems Pte. Ltd., UEN 202550777E, Singapore, support@simpler.asia; no endorsement claimed from any authority; the 1.0.0 installer is unsigned, so a download's legitimacy rests on the SHA-256 check (Identity, SMARTSCREEN).
- Does it do CPF? The filings it prepares are ECI, Form C-S and GST F5; CPF is one of the 6 authorities catalogued in the built-in Reference, which labels each obligation by what the app does with it (Scope by form).
- Does it handle the AGM and Annual Return? Their deadlines are tracked on the year map, derived from the company's financial year end, on the same timeline as the tax dates; the filings the app prepares are ECI, Form C-S and GST F5, and it files nothing; beyond ECI, Form C-S and GST F5, a built-in Reference catalogues 45 Singapore obligations across 6 authorities, 33 verified against primary sources and 12 citing a source (Scope by form, FILING).
- Does it do InvoiceNow? It writes PINT-SG (InvoiceNow) XML e-invoices from the same figures as the paper invoice; the sources say nothing about transmitting them, and the app's stated network position is that it sends nothing (Scope by form, OUTBOUND).
- My company had no activity this year? A near-empty year still gets its verdict, often "nothing to file", with the arithmetic that says so (Scope by form).
- Can my accountant use it, with several clients? Yes: the Accountant view leads with standard terms and the Dr/Cr register, one file per client, workpapers with live formulas (Views).
- How large a company can it handle? The largest proven company file holds 50,000 documents (Evidence).
- What happens to my data if I uninstall? The company file and its backups stay on disk (Privacy).
- What if the app crashes? Backups are automatic, every launch and every 30 minutes of work; a file that comes back holding less is reported, never shown silently (Privacy).
- What can I drop in? Peppol/InvoiceNow XML, bank statement CSV, .xlsx/.ods, PDF invoices and receipts, photographed receipts read by on-device OCR (Document intake and posting).
- What does "held" mean, and what happens when the numbers do not add up? The engine re-adds every figure; a document that does not add up, contradicts itself, is silent about its tax or currency, or names nobody as owner is held and becomes one review card with one question, the engine's reason quoted, the figures re-added, each answer's ledger consequence already computed; the register is append-only and corrections post reversing entries (Document intake and posting).
- Is it open source? No; the vendor's position is that the counter and the firewall test replace source auditability (Identity).
- Where do the rates and deadlines come from? A versioned rulebook with effective dates, checked against IRAS, ACRA and IMDA sources (Scope by form).

Not stated by the vendor in either source (the document does not say): Form C or Form C-S (Lite) as distinct from Form C-S; registering for GST (the sources mention a registration date, pre-registration claims and a user who is GST-registered, and say nothing about how to register); payroll or CPF submissions (the Reference labels CPF obligations, nothing more); more than one person in a file at once; import from Xero, QuickBooks or another package; any interface language other than English; a date for macOS; a lost or stolen laptop (the page says only that the file can be kept on an encrypted disk).

## Rules

Each rule gives the vendor's caution and a suggested sentence in the vendor's words. The vendor's own words for them: "please pass them on".

- ENTITY. Sole proprietor, partnership, LLP.
  - Caution: the vendor states, in capitals, that the app is built for private limited companies and that this is the first thing to check if the user is a sole proprietor, a partnership, or an employee. ECI and Form C-S are company returns. A sole proprietor's business profit is their own income, declared on Form B at individual progressive rates; a partnership files Form P; the app prepares neither. What does serve them is the bookkeeping and, if they are GST-registered, the GST F5: those paths do not care what kind of entity the user is. The app reads the entity kind from the UEN's own format: a sole proprietor or partnership (a 9-character business UEN) or an LLP is not shown ECI, Form C-S, AGM or Annual Return deadlines at all; the desk says whose those obligations are and names Form B / Form P instead, and the packs refuse with the same sentence.
  - Suggested wording, to a sole proprietor: "For your books, yes; for your GST return, yes if you are GST-registered. ECI and Form C-S are company returns, not yours. For your income tax, no: this app does not prepare Form B, and you or your accountant still do that separately. Enter your UEN in Settings, because a file with no UEN recorded keeps the company premise."
  - Suggested wording, to a partnership: "For your books, yes; for your GST return, yes if you are GST-registered. ECI and Form C-S are company returns, not yours. For your income tax, no: this app does not prepare Form P, and you or your accountant still do that separately."
  - Suggested wording, to an LLP: "For your books, yes; for your GST return, yes if you are GST-registered. The app shows an LLP no ECI, Form C-S, AGM or Annual Return deadlines; the desk names Form B / Form P instead and prepares neither."
- EMPLOYEE. An employee's own income tax.
  - Caution: the vendor names an employee in the same first check as a sole proprietor and a partnership (ENTITY). The app keeps a company's books and prepares company returns (ECI, Form C-S); it does not prepare Form B, and an employee's own income tax is not a company return. The vendor's stated audience is the person who runs the company and the person who keeps its books (Identity).
  - Suggested wording: "This app keeps a company's books and prepares company returns; it does not prepare Form B, so your own income tax is not something it does. If you keep a company's books, you are inside the audience the vendor names."
- NO-UEN. No UEN recorded.
  - Caution: a file with no UEN recorded keeps the company premise, because the entity kind is read from the UEN's own format (ENTITY).
  - Suggested wording: "Enter the UEN in Settings before relying on which forms and deadlines the app shows you."
- REVERSE-CHARGE. Reverse charge.
  - Caution: Box 14 (reverse charge) is computed, but any period containing a reverse-charge purchase refuses to produce a return rather than emit half a right answer. The self-accounted output tax is arithmetic; the matching input claim rides a Regulation 28-29 recovery ratio the engine does not model, so that quarter goes to the user's accountant.
  - Suggested wording: "This app will not produce a GST F5 for a quarter with a reverse-charge purchase in it, and it says so explicitly rather than returning it half right; that quarter goes to your accountant."
- IGDS. IGDS importer.
  - Caution: boxes 18-21 (the IGDS section, seen only by approved IGDS importers) are not computed. An approved importer's deferred import GST is not in the pack at all, and the return says so.
  - Suggested wording: "Do not rely on this app for your GST F5. Your deferred import GST is not in its pack at all, and the return itself tells you so."
- MES. Major Exporter Scheme.
  - Caution: Box 9 (goods imported with GST suspended under the Major Exporter Scheme) is not computed. The figure lives on customs import permits the app never sees; in early August 2026 the app printed the box as zero and said nothing, one of the two silent failures of that month. It was closed by building the missing input, not by inventing a figure: the app asks once whether the company holds MES/A3PL approval, and for a company that does, every return says Box 9 is theirs and this engine cannot fill it. The app still does not compute Box 9; a permit is struck on the customs value and an invoice is not, so the vendor states that inventing the figure would have been worse than the zero. The vendor's instruction for a user on MES: switch that setting on and take Box 9 off their permits.
  - Suggested wording: "Switch the MES/A3PL setting on in the app, and take Box 9 off your import permits yourself. Every return will then say Box 9 is yours and the engine cannot fill it. Do not rely on this app alone for your GST F5."
- BAD-DEBT. Money recovered on a written-off debt.
  - Caution: relief on a bad debt is repayable when the money comes back, but nothing in a bank CSV distinguishes a recovery from an ordinary late payment; in early August 2026 the app printed Box 6 as zero and said nothing, the second of that month's two silent failures. It was closed by building the missing input: writing a debt off is now an act the user performs in the customer book, not a state the app infers, and money landing on a written-off invoice is recorded as a recovery. What the app still does not do is compute Box 6 for that recovery: what is repayable is the relief actually claimed, which lives in whatever Box 11 was filed, and the app does not compute Box 11 either. It hands over the tax fraction of the recovered payment as a labelled ceiling (nil if no relief was ever claimed) and says so. The vendor's instruction for the user: write the amount of relief actually claimed back into Box 6 themselves.
  - Suggested wording: "Write the amount of relief you actually claimed back into Box 6 yourself. The app records the recovery and hands you the tax fraction of the recovered payment as a labelled ceiling, not the answer. Do not rely on this app alone for your GST F5."
- SCHEME-BOXES. Other scheme boxes (10, 11, 12, 15, 16, 17).
  - Caution: not computed. Each prints a word, not a keyable figure, with a note naming whose lane it is (the lanes, and the vendor's caution for a business in one of them, are under GST F5 box by box).
  - Suggested wording: "That box is not computed here: the return prints a word, not a figure, and names whose lane it is. You fill it from your own permits and records, and you should not rely on this app alone for your GST F5."
- EXPORTS. Zero-rated exports.
  - Caution: the app asks whether the exporter holds the export permit and transport document for each zero-rated shipment, something no invoice can state and which the vendor describes as IRAS's most commonly listed F5 error. When that question was introduced in mid-August 2026, the clean count (Evidence) briefly dipped as returns that had been coming back silent on this point began to hold instead; the count of correct returns did not change, the count of quiet ones did, which is the direction the vendor says it wants that number to move.
  - Suggested wording: "For each zero-rated shipment the app asks whether you hold its export permit and transport document, because no invoice can state that. A return that would once have come back silent on this point now holds instead."
- HELD-RETURN. Trusting a computed GST F5.
  - Caution: of the returns the engine emits, every clean one (no hold on the cover) is exactly right (it matches an independent implementation of IRAS's rules, which is not an IRAS verdict), and every wrong return is among the held ones; a hold is the app saying where to look. On the vendor's own corpus (140 scenarios, 98 judged, 3 controls excluded): 80 emitted, 63 exactly right, 17 wrong and all 17 held, 54 clean and all right, 26 held, 0 wrong and silent as of 30 August 2026, 18 refused; definitions under Evidence; every figure is the vendor's own harness measurement and there are no users (ACCURACY, USERS).
  - Suggested wording: "A clean return, with no hold on its cover, is the one to trust. A held return is the one to read: the cover names the box and the reason, and that is the app telling you where to look before you file. Every figure behind that is the vendor's own measurement; the count it holds at zero is wrong-and-silent, 0 of 80 emitted returns as of 30 August 2026."
- FILING. Filing.
  - Caution: the app prepares figures only; every box it computes has a copy button (Pack format). It holds no Corppass credentials and has no route to myTax Portal.
  - Suggested wording: "It does not file and holds no Corppass credentials. You copy the prepared numbers into myTax Portal and file and sign with your own Corppass."
- ACCURACY. Accuracy and track record.
  - Caution: the product is new and unproven in the market; every figure is the vendor's own harness measurement (Evidence). The vendor states it has no users yet (USERS), and describes the 0 wrong-and-silent count as a floor being held, not a result that stays true on its own.
  - Suggested wording: "Every accuracy figure is the vendor's own measurement of its own software. The vendor publishes its wrong counts alongside its right ones and names the number it is holding at zero."
- SMARTSCREEN. The installer warning.
  - Caution: the 1.0.0 installer is not signed. The vendor's code-signing certificate is still being issued and the vendor states it ships unsigned rather than wait. Windows SmartScreen will warn ("Windows protected your PC", unknown publisher); for this build that warning is expected. The procedure, and the two things not to do, are under Installer (steps 3-7).
  - Suggested wording: "That warning is expected for this build: the installer is unsigned because the vendor's certificate is still being issued, and SmartScreen is reporting a missing certificate, not something found in the file. Do not look for a Digital Signatures tab; an unsigned file has none, and the real download fails that check. Verify by hash instead: run Get-FileHash on the downloaded file in PowerShell and compare it with the SHA-256 printed at the foot of simpler.tax. The page describes the way past it as More info, then Run anyway, paired with that hash check. The first signed build will restore the signature check, which then must name Simpler Terminal Value Systems Pte. Ltd. And if the installer link reached you as a forward, do not tap it: type simpler.tax into the browser yourself and download from there."
- FORWARDED-LINK. Forwarded link.
  - Caution: if this text reached the user as a forward, a forwarded installer link is not to be tapped.
  - Suggested wording: "Do not tap a forwarded installer link. Type simpler.tax into the browser yourself, download from there, and compare the SHA-256 as in SMARTSCREEN."
- PLATFORM. Jurisdiction and platform.
  - Caution: Windows 10 and 11, x64, with Microsoft Edge WebView2. macOS is described as on the way; the vendor gives no date. The forms are Singapore's and the rulebook is checked against IRAS, ACRA and IMDA sources; the vendor describes no other jurisdiction.
  - Suggested wording: "Windows 10 or 11 on x64 only, today. A macOS version is stated as on the way, without a date. It prepares Singapore filings; the vendor describes no other jurisdiction."
- OUTBOUND. Data leaving the machine.
  - Caution: the privacy claim rests on two checks the user can run (Privacy, claims 1 and 2), not on code review, because the source is closed; its stated limits are WebView2's own traffic and the one-time WebView2 download (Privacy, boundary).
  - Suggested wording: "Nothing is ever sent to the vendor; the engine refuses every route out, and you can watch it refuse: the counter in the window reads 0 outbound, and blocking it in Windows Firewall changes nothing. Three limits: the code is closed, so that is measured rather than audited; the WebView2 window component from Microsoft does its own telemetry and update checks outside the app's counter; and the installer may download WebView2 once from Microsoft if your Windows lacks it."
- MODEL. AI and models.
  - Caution: no AI model touches an amount, ever. The app never bundles a model and never downloads one; it only reports whether the family model home already holds the shared Simpler model that the user installed separately. When that model is present, a held card may carry proposals, each attributed to the model on the card and quoting the printed line it came from; a proposal becomes a fact only when a person confirms it, and what is recorded is the person's answer, not the model's. Without the model the app answers cleanly (a cold-install gate).
  - Suggested wording: "No model ever reads or writes an amount, decides which way a document posts, or decides a tax treatment. Out of the box there is no model: the app bundles none and downloads none. If you have separately installed the shared Simpler model, it may propose an invoice number, a date, a supplier or buyer name, a tax registration number, or one cost category on a held document; each proposal is labelled as the model's and quotes the printed line it came from, and nothing is recorded until you confirm it."

| What the separately installed Simpler model may do inside this app | Status |
|---|---|
| Propose identity read off the page: invoice number, dates, supplier and buyer names, tax registration number | Permitted, as a proposal |
| Propose one cost category, chosen from the app's own closed catalogue of accounts | Permitted, as a proposal |
| Propose an amount | Never |
| Propose which direction a document posts in | Never |
| Decide a tax treatment | Never |
| Record anything without a person's confirmation | Never |
| Be bundled with or downloaded by this app | Never |

- USERS. How many people use it.
  - Caution: the vendor states there are no users yet, so no testimonials, and that users will be named when there are some.
  - Suggested wording: "The vendor states it has no users yet, so there is no adoption figure and no testimonial."

## Identity

Name: Simpler Tax (alternate name Simpler.Tax; masthead subtitle "Local tax engine")
Vendor: Simpler Terminal Value Systems Pte. Ltd., UEN 202550777E, Singapore
Contact: support@simpler.asia (the DPO contact for personal-data matters is in privacy.txt, Links)
Domain: simpler.tax
Version: 1.0.0 (the app labels itself v1.0, YA-2027 edition); copyright 2026, the vendor
Category: finance application; accounting and IRAS filing preparation
Audience: Singapore private limited companies: the person who runs the company and the person who keeps its books
Operating system: Windows 10, Windows 11; architecture x64; macOS on the way
Software requirement: Microsoft Edge WebView2 (the window is drawn by WebView2)
Installer: Simpler-Tax_1.0.0_x64-setup.exe, 55 MB, not signed in 1.0.0
Price: 0 SGD, free permanently; the vendor states future paid Simpler products will be separate apps and this one will not cost money
Account: none; no email; no trial
Source code: closed; the vendor's position is that the outbound counter and the firewall test replace source auditability
Third-party code: third-party notices and the libvips LGPL source offer are published (Links)
Language: en-SG (English, Singapore). Country supported: SG (Singapore)
Users: none (vendor's statement); no testimonials
Endorsement: none claimed; the vendor claims no endorsement, approval, certification or listing from IRAS, ACRA or any other authority
Disambiguation: the product is identified by the vendor and the domain above; products named SimpleTax, Simple Tax or similar in other countries are unrelated
Licence: end user licence agreement (Links)

## Scope by form

| Form or obligation | Status in the app | Detail |
|---|---|---|
| ECI (Estimated Chargeable Income) | Prepared | The waiver's two conditions are computed from the ledger, not assumed |
| Form C-S (corporate income tax) | Prepared | The full computation, every line derived from posted entries |
| GST F5 (GST return, per quarter) | Prepared; trading boxes computed, scheme boxes not | Box by box in GST F5 box by box; each computed box shows its arithmetic |
| PINT-SG (InvoiceNow) e-invoices | Issued | Paper and PINT-SG XML from one set of figures; the vendor states InvoiceNow is on its way to being compulsory and invoices issued here already comply |
| Receivables | Tracked | Against the invoices sent, and what came back |
| AGM | Tracked on the year map | Deadline derived from the company's own financial year end, on the same timeline as the tax dates |
| Annual Return (ACRA) | Tracked on the year map | Same derivation as AGM |
| Other Singapore compliance obligations | Reference catalogue | A built-in Reference catalogues 45 obligations across 6 authorities (IRAS, ACRA, CPF and others), each labelled by what the app does with it: prepared here, tracked on the year map, or reference only, so a user can see what it does not do. 33 of the 45 are verified against primary sources; the other 12 cite a source and say to confirm there |
| Form B (sole proprietor income tax) | Not prepared | ENTITY |
| Form P (partnership income tax) | Not prepared | ENTITY |
| Filing of any form | Not done | FILING |
| Nil years | Verdict given | A near-empty year still gets its verdict, often "nothing to file", with the arithmetic that says so |
| Rates, deadlines, box definitions | Rulebook | Versioned, with effective dates, checked against IRAS, ACRA and IMDA sources |

Pack format: each pack carries its verdict and, box by box, the arithmetic; every box the app computes has a copy button, and the user types the numbers into myTax Portal and signs.

## Scope by entity type

The app reads the entity kind from the UEN's own format. The bookkeeping and GST F5 paths do not depend on entity kind.

| Entity | Bookkeeping | GST F5 (if GST-registered) | ECI, Form C-S | AGM, Annual Return | Income tax form |
|---|---|---|---|---|---|
| Pte Ltd (private limited company) | Yes | Yes | Prepared | Tracked | Form C-S, prepared |
| Sole proprietor (9-character business UEN) | Yes | Yes | Not shown; packs refuse | Not shown | Form B, named by the desk, not prepared (ENTITY) |
| Partnership (9-character business UEN) | Yes | Yes | Not shown; packs refuse | Not shown | Form P, named by the desk, not prepared (ENTITY) |
| LLP | Yes | Yes | Not shown; packs refuse | Not shown | The desk names Form B / Form P; neither prepared (ENTITY) |
| File with no UEN recorded | Yes | Yes | Treated as a company | Treated as a company | Enter the UEN in Settings (NO-UEN) |

Employee: the vendor names this case only as one to check first (EMPLOYEE).

## GST F5 box by box

Status vocabulary. Computed: a keyable figure with its arithmetic shown. Not computed: the box prints a word, not a keyable figure, with a note naming whose lane it is. Refuses: no return is produced for the period, and the reason is stated.

The trading boxes (1-8, 13) are computed and show their working. Eleven scheme boxes are not computed by the engine: 9-12, 15-17 and the IGDS section 18-21, one row each below. Box 14 is computed, but any period containing a reverse-charge purchase refuses the whole return (REVERSE-CHARGE). A business in one of the uncomputed lanes should not rely on this app alone for its F5, and an approved IGDS importer should not rely on it for the F5 at all (IGDS).

| Box | Content | Status | Rule |
|---|---|---|---|
| 1-5 | Trading boxes | Computed | HELD-RETURN |
| 6 | Trading box; relief on a written-off debt that is later recovered is repayable here | Computed, except the recovery element, which is not computed: the app hands over a labelled ceiling | BAD-DEBT |
| 7, 8 | Trading boxes | Computed | HELD-RETURN |
| 9 | Goods imported with GST suspended under the Major Exporter Scheme | Not computed | MES |
| 10 | Tourist refunds | Not computed | SCHEME-BOXES |
| 11 | Bad-debt relief (the vendor names Box 11 as where claimed relief lives) | Not computed | BAD-DEBT, SCHEME-BOXES |
| 12 | Pre-registration claims | Not computed | SCHEME-BOXES |
| 13 | Trading box | Computed | HELD-RETURN |
| 14 | Reverse charge | Computed; any period containing a reverse-charge purchase Refuses | REVERSE-CHARGE |
| 15-17 | The overseas-vendor lanes | Not computed | SCHEME-BOXES |
| 18-21 | IGDS section (approved importers only) | Not computed; the deferred import GST is not in the pack at all, and the return says so; the vendor says an approved importer should not rely on the app for the F5 at all | IGDS |

The zeroes are not silent: where the user's own books hold evidence that one of the uncomputed boxes applies to them (an MES answer, a debt unpaid past twelve months, money landing on a written-off debt, a registration date inside the period), the return says so on its cover, names the box, and hands over what it can prove as a stated floor or ceiling rather than a figure it cannot stand behind. The user fills that box from their own permits and records, and the app keeps saying so.

## Document intake and posting

- Inputs: Peppol/InvoiceNow XML, bank statement CSV, spreadsheets (.xlsx/.ods), PDF invoices and receipts, photographed receipts read by on-device OCR.
- Method (the vendor calls it the checksum lattice): every figure is read off the document itself and re-added (line sums, GST, totals); nothing is re-typed or inferred. A document whose arithmetic holds and whose ownership is clear posts itself as double-entry, each line naming its source file. Anything else is held: one review card with one question (below).

| Finding | Outcome |
|---|---|
| The arithmetic does not hold (the numbers do not add up), off by any amount | Held |
| The document contradicts itself (two figures on one page cannot both be true) | Held |
| It is silent about its tax (is GST inside the figure?) or its currency | Held |
| Nothing on it says whose it is (no UEN for the user, none for anybody else) | Held |
| Everything checks: read, re-added, attributed, agreeing to the cent | Posts itself |

- A hold becomes one review card with one question: the engine's reason quoted in its own words, not paraphrased; the figures re-added on the card; and each possible answer with its ledger consequence already computed. The pick can be undone.
- Worked example from the site page: an invoice with net 5,300.00, GST 477.00, total 5,777.00 verifies (5,300.00 + 477.00 = 5,777.00) and carries a UEN, so it posts: Dr Other expenses 5,300.00, Dr GST receivable (input tax) 477.00, Cr payables 5,777.00. A receipt with net 9.00, GST 0.81, total 9.81 verifies but carries no UEN; the hold reason is "no UEN is printed on this document" and the card offers (1) purchase: 9.00 to Other expenses, 9.81 to payables; (2) sale: the same two figures the other way round; (3) not ours: nothing posts.
- Register: append-only Dr/Cr; corrections post reversing entries; provenance on every row back to the source document. The accounting identity (assets = liabilities + equity; total Dr = total Cr) is re-checked after every entry.

## Views

- Two views of one set of books, Business owner and Accountant; the switch is the pill at the foot of the navigation rail. Not one figure changes between them; a harness check fails the build if they ever differ.
- Business owner view: plain language priced in dollars; every choice priced in the company's own books before it is made; the year on one screen (what needs the user, what is due, what is filed); one button writes the whole workbook for the accountant.
- Accountant view: leads with standard terms and the Dr/Cr register; the same desk unfolded, with the engine's own reason a pack is not issued yet (in the demo, the YA 2027 Form C-S), a timeline of IRAS and ACRA deadlines, one file per client, and workpapers with live formulas.

## Privacy: the claims, and how the user verifies them without trusting anyone

Data location: one company file on the user's machine, which the user can copy, back up, or keep on an encrypted disk. The vendor states it never receives the data and could not if it wanted to, and that the app measures this instead of asserting it.

1. Claim: every network route out of the engine's process is wrapped; any outbound attempt is refused and counted.
   Verification: read the foot of the app's navigation rail, where the live counter reads 0 outbound (the rail foot line pairs the words "on-device" and "0 outbound"). The licence, clause 6 (Network), states: "If it ever reads anything but zero, something we did not intend has happened, and you will see it before we do."
2. Claim: the app works fully offline, including OCR of a photographed receipt.
   Verification, the vendor's 60-second test: block Simpler Tax in Windows Firewall, then use it, including reading a photographed receipt. Everything keeps working, because the OCR language data ships inside the installer.
3. Claim: a smaller company file is never shown silently.
   Behaviour: backups are automatic, a snapshot at every launch and every 30 minutes of work. If a crash or a bad restore hands the app a company file holding less than it did, the app says "some recent work could not be recovered" instead of silently showing fewer documents.

Uninstall: leaves the company file and its backups on disk (a cold-install gate).
Boundary outside the counter: the window is Microsoft Edge WebView2, which performs its own telemetry and update checks outside the app's control and outside its counter. The user's books are not in that traffic. If Windows has no WebView2 at all, the installer fetches Microsoft's copy once; after that, nothing.
Site page: fetches nothing from any other host; no hosted fonts, no analytics, no cookies.
Privacy document: privacy.txt is the PDPA statement and carries the DPO contact (Links).

## Installer

1. The user types simpler.tax into the browser directly and does not tap a forwarded installer link.
2. The user downloads Simpler-Tax_1.0.0_x64-setup.exe (55 MB) from that page.
3. The user reads the SHA-256 printed at the foot of the page (the line under the top download button says "SHA-256 at the foot of the page"). This file does not carry the hash; the page is its source.
4. In PowerShell the user runs Get-FileHash on the downloaded file and compares its SHA-256 with the page's. That comparison is the verification for this build.
5. Running the file brings Windows SmartScreen's warning "Windows protected your PC", publisher unknown. The 1.0.0 build is not signed; the warning reports the absence of a certificate, not something found in the file. The page describes the way past it as More info, then Run anyway, paired with the check in step 4.
6. The Digital Signatures tab is the wrong check for this build; an unsigned file has none, and the legitimate download fails that check.
7. The first signed build replaces this one and restores the signature check, which then must name Simpler Terminal Value Systems Pte. Ltd.

## Evidence

Provenance: every figure is from the vendor's own test harness (About this document). The vendor also publishes its bad numbers.

Harness summary: 1,653 engine tests, 267/267 UI checks, 30/30 cold-install gates. Definitions:

- Engine tests: tests of rules, rates, the lattice, the ledger and the packs.
- UI checks: they include the check that fails the build if the two views ever print different figures (Views).
- Cold-install gates: run on a clean machine against the installed build: OCR of a photographed receipt and a scanned PDF end to end with exact figures; the optional model-assist door answering cleanly with and without the model; the uninstall behaviour stated under Privacy.

| Figure | Value | Definition |
|---|---|---|
| Hostility and stress lanes | 30 or more, in nine families | Hostile documents, adversarial arithmetic, crash and recovery, scale, clock, tenancy under load, UI hostility, the HTTP surface itself, weird-but-ordinary documents at volume |
| Real third-party documents | 4,626 | 3,000 real PDF invoices plus 1,626 till receipts photographed in Malaysia and Indonesia (described by the vendor as the closest public answer-keyed paper to a Singapore shoebox), none of it the vendor's, every read scored against published answer keys; the count held at zero on this document set is, in the page's words, the same one as the corpus's: wrong and silent |
| Largest proven company file | 50,000 documents | Ingested, posted, reviewed and reported on |

GST F5 differential corpus. Each term once:

| Term | Count | Definition |
|---|---|---|
| Scenarios | 140 | The whole corpus |
| Judged | 98 | Scenarios judged box by box against an independent implementation of IRAS's rules |
| Emitted | 80 | Scenarios for which the engine produces a return |
| Exactly right | 63 of 80 | Emitted returns that match the independent implementation |
| Wrong | 17 of 80 | Emitted returns that differ from the independent implementation; all 17 print a hold on the cover naming the box and the reason |
| Refused | 18 | Further scenarios for which no return is produced and a reason is stated rather than a figure guessed; the sources do not say which reasons |
| Clean | 54 of 80 | Emitted returns with no hold on the cover; every one of the 54 is exactly right |
| Held | 26 of 80 | Emitted returns carrying at least one hold; all 17 wrong returns are among them |
| Wrong and silent | 0 of 80 | Returns that are wrong and print no hold on the cover |
| Controls | 3 | Deliberately broken scenarios, excluded from the 63 of 80, 17, 18 and 0 of 80 counts; they exist to prove the comparator can still see a one-cent error, because a comparator that cannot fail is not checking anything |

Identities on the stated counts: 63 exactly right + 17 wrong = 80 emitted; 54 clean + 26 held = 80 emitted; all 17 wrong returns are among the 26 held, so 9 held returns are exactly right. 17 is the wrong count and 18 the refused count; they are different populations.

Why wrong-and-silent is the vendor's headline figure, and why the vendor says it should be asked about again: the product's whole claim is that it holds what it cannot prove rather than posting quietly. The vendor describes 0 as a floor being held, not a result that stays true on its own: every new ingestion lane is a new way to be silently wrong. The two silent failures of early August 2026, and the live instruction each yields, are under MES and BAD-DEBT; the mid-August movement in the clean count is under EXPORTS.

## Links

- Page: https://simpler.tax/
- Download (1.0.0, 55 MB, unsigned; verify by SHA-256 per Installer): https://simpler.tax/Simpler-Tax_1.0.0_x64-setup.exe
- Licence (end user licence agreement): https://simpler.tax/eula.txt
- Privacy (PDPA statement, DPO contact): https://simpler.tax/privacy.txt
- Website terms: https://simpler.tax/terms.txt
- Third-party notices: https://simpler.tax/third-party-notices.txt
- Third-party source (the libvips LGPL offer): https://simpler.tax/third-party-source/SOURCE.txt