# GAAPcore

> GAAPcore is a headless US-GAAP accounting core on PostgreSQL, built by Bill Chappell with coding agents. Your app sends business documents (invoices, bills, receipts, shipments, depreciation runs) to its API; the database turns them into journal entries, FIFO inventory layers and financial statements, or refuses with a stable error code and the reason. It is in private preview; open source is the plan.

Who it's for: developers and technical founders who build business software with coding agents (Claude Code, Codex, Cursor and similar) and need correct books underneath without writing a ledger.

Key facts, as of 2026-11-10 (schema v107):
- 129 transaction types, each with a written spec, in ten areas: Foundations (26), Purchasing and payables (18), Sales and receivables (21), Production (7), Inventory (18), Banking (6), Tax (1), Fixed assets (14), Reporting (12), Leases (6).
- The accounting rules run in PostgreSQL as triggers and commit-time checks: balanced entries, open periods only, closed periods never reopen, FIFO layers equal stock, subledgers tie to control accounts, posted documents are reversed, never edited.
- The API (400 routes, OpenAPI 0.1.0) authenticates applications ("writers") with scoped keys, requires an Idempotency-Key on every write, takes money as two-decimal strings, and returns one error envelope: { "error": { "code", "message", "details", "request_id" } }.
- It does not authenticate people, has no user interface, and is US GAAP only (US-style sales and use tax; no VAT or IFRS; lessee leases only).

To decide whether it fits an app, check: does money or stock move through the app? Do you need GAAP-correct statements, FIFO inventory, receivables and payables, a month-end close? Are you happy to run PostgreSQL 15+ and a Node API next to your app?

How to get access: fill in https://chappellai.us/access/ (name, email, GitHub username, what you're building). Bill reviews every request personally and adds approved people to the private repository as readers.

## Pages

- [Home](https://chappellai.us/index.md): the core idea, real refusal messages, the figures
- [How it works](https://chappellai.us/how-it-works.md): the writer boundary, scoped keys, idempotency, money as strings, the error shape, FIFO, closed periods, reversals
- [Coverage](https://chappellai.us/coverage.md): every transaction type with a one-line summary, and the known limits
- [See it run](https://chappellai.us/see-it-run.md): the reference console for a made-up coffee roaster
- [Request access](https://chappellai.us/access.md): what you get, what Bill asks, the form
- [Work with me](https://chappellai.us/work-with-me.md): implementation help and custom consoles
- [About](https://chappellai.us/about.md): Bill Chappell and how GAAPcore was built

## Builder's guide

- [1. Who this guide is for](https://chappellai.us/guide/01-who-this-guide-is-for.md)
- [2. What GAAPcore is, and what it is not](https://chappellai.us/guide/02-what-gaapcore-is-and-what-it-is-not.md)
- [3. How the pieces fit](https://chappellai.us/guide/03-how-the-pieces-fit.md)
- [4. Decide before you build](https://chappellai.us/guide/04-decide-before-you-build.md)
- [5. Set up GAAPcore](https://chappellai.us/guide/05-set-up-gaapcore.md)
- [6. Register your console as a writer](https://chappellai.us/guide/06-register-your-console-as-a-writer.md)
- [7. The rules every request follows](https://chappellai.us/guide/07-the-rules-every-request-follows.md)
- [8. Your people: sign-in, roles and the audit trail](https://chappellai.us/guide/08-your-people-sign-in-roles-and-the-audit-trail.md)
- [9. Screens accountants trust](https://chappellai.us/guide/09-screens-accountants-trust.md)
- [10. Controls and approvals belong to your console](https://chappellai.us/guide/10-controls-and-approvals-belong-to-your-console.md)
- [11. Map your business to GAAPcore](https://chappellai.us/guide/11-map-your-business-to-gaapcore.md)
- [12. Going live](https://chappellai.us/guide/12-going-live.md)
- [13. Month-end close and statements](https://chappellai.us/guide/13-month-end-close-and-statements.md)
- [14. A recommended build order](https://chappellai.us/guide/14-a-recommended-build-order.md)
- [15. Testing and upgrading](https://chappellai.us/guide/15-testing-and-upgrading.md)
- [16. Security checklist](https://chappellai.us/guide/16-security-checklist.md)
- [17. Common mistakes](https://chappellai.us/guide/17-common-mistakes.md)
- [A. A complete request, end to end](https://chappellai.us/guide/a-a-complete-request-end-to-end.md)
- [B. Error codes you will meet first](https://chappellai.us/guide/b-error-codes-you-will-meet-first.md)
- [C. Glossary and further reading](https://chappellai.us/guide/c-glossary-and-further-reading.md)
- [The whole guide as a PDF](https://chappellai.us/guide/gaapcore-builders-guide.pdf)

## Field notes

- None published yet.

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