Best of · Domain data
Best accounting and invoicing APIs for AI agents
The 10 highest-scoring of 12 accounting and invoicing APIs on the Anchor benchmark, with a pick for each need and where each one falls short. Scores come from public evidence, re-checked as vendors change.
- 12 ranked
- 2 agent-ready
- 11 hosted endpoints
- Updated 9 October 2026
Top three
Picks by need
Worked out from the scores, prices and facts, so they change when the research does.
Highest score overall
Apideck Accounting API + MCP BB
BB, 72.9/100 on the benchmark.
Also Merge Accounting API, BB, 70/100.
Maintenance & community
85/100 on maintenance & community, against 80 for the overall leader.
Transparency & trust
93/100 on transparency & trust, against 73 for the overall leader.
Self-hosting under an open licence
self-hosted, Community edition LGPL-3 licence.
Also Invoice Ninja API, self-hosted, Elastic License 2 licence.
The shortlist
| # | Tool | Grade | Best for | Price | Where |
|---|---|---|---|---|---|
| 1 | Apideck Accounting API + MCP Apideck |
BB 72.9 | A SaaS product that has to reach many customers' ledgers, especially European or desktop ones, through one agent-friendly MCP. | $599 / mo | hosted and local |
| 2 | Merge Accounting API Merge |
BB 70 | A SaaS product that reads and writes many customers' ledgers through one model and wants docs an agent can read cheaply. | $650 / mo | hosted |
| 3 | Xero API + MCP Xero |
B 67.2 | An agent keeping the books for UK, Australian or New Zealand businesses, or any team that wants read-only scopes and long deprecation notice. | Freemium | hosted and local |
| 4 | Pennylane Pennylane SAS |
B 66.3 | An agent working on the books of French companies or an accounting firm's client portfolio, with French chart of accounts, FEC export, Factur-X e-invoicing and VAT returns. | Paid | hosted |
| 5 | Codat Codat Limited |
B 64.3 | Banks, lenders, bill pay, expense and card products that already have or will sign a Codat contract and need writes into many accounting packages. | Paid | hosted |
| 6 | Zoho Books Zoho |
C 61.1 | Small businesses already on Zoho that want an agent to raise invoices, record bills and payments, reconcile bank transactions and post journals with narrow scopes. | $15 / mo | hosted |
| 7 | FreeAgent API FreeAgent |
C 57.2 | An agent doing the books for a UK freelancer or small limited company, especially one already banking with NatWest. | Your plan | hosted |
| 8 | Odoo External API Odoo SA |
C 55.9 | An agent working inside a company that already runs Odoo, where invoices, bills, journal entries, stock and sales sit in one database behind one endpoint pattern. | Paid | local |
| 9 | Rutter Accounting API Rutter |
C 55.6 | Lenders, spend-management and fintech products that read ledgers alongside commerce and payment platforms, and that need writes an agent can retry safely. | Paid | hosted |
| 10 | Invoice Ninja API Invoice Ninja |
D 52.1 | An agent that quotes, invoices, chases and records payments for a small business, or for anyone who wants the billing system on their own server. | $14 / mo | hosted |
2 more are ranked in the full table.
How to choose
- Objects covered and write accessCheck which objects can be read and which can be written, since a bill or payment you cannot post leaves the agent able to report but not to record.
- Direct or unified connectionCheck whether the API connects to the accounting package your client uses or goes through a unified layer, since coverage and access can differ between the two.
- Rate limits and error handlingCheck the rate limits and how errors come back, including retry guidance and idempotency, since a sync that retries a failed invoice can create duplicates in the ledger.
- Sandbox and report accessConfirm a sandbox company can run the full flow and that reports are readable, since an agent should test invoices and bills before real books change.
How the benchmark tests this category. An agent creates a customer and an invoice, records a payment, reads a profit and loss report and posts a bill in a sandbox company. We check which steps work, the rate limits and how errors come back.
Each one in detail
Apideck Accounting API + MCP
BB 72.9/100Unified accounting API for invoices, bills, payments, journal entries and financial reports across platforms including QuickBooks, Xero and NetSuite.
Verdict 56 accounting connectors, including European ledgers such as DATEV, Exact Online, Fortnox and Twinfield. No published rate limits of Apideck's own, only connector limits mirrored in headers.
Choose it for A SaaS product that has to reach many customers' ledgers, especially European or desktop ones, through one agent-friendly MCP.
Strengths
- 56 accounting connectors, including European ledgers such as DATEV, Exact Online, Fortnox and Twinfield
- Dynamic MCP mode with 4 meta-tools at about 1,300 tokens, and annotations on all 362 tools
- Public OpenAPI spec (accounting.yml, 208 operations) with a dated changelog and a BREAKING.md for removals
Weaknesses
- No published rate limits of Apideck's own, only connector limits mirrored in headers
- No idempotency keys on writes, so a timed-out create can duplicate
- $599 a month for 25 customers after the trial, no free tier
Price $599 / moAuth API keyx402 nohosted and local
Merge Accounting API
BB 70/100Unified accounting API for invoices, payments, expenses, journal entries and financial statements across platforms including QuickBooks, Xero and NetSuite.
Verdict 12 accounting platforms behind one set of common models, with writes. Launch jumps from free to $650 a month at the fourth linked account.
Choose it for A SaaS product that reads and writes many customers' ledgers through one model and wants docs an agent can read cheaply.
Strengths
- 12 accounting platforms behind one set of common models, with writes
- Three production linked accounts free with no card
- llms.txt, Markdown twins of every docs page and a JSON OpenAPI spec
Weaknesses
- Launch jumps from free to $650 a month at the fourth linked account
- No documented 429 handling, idempotency keys or safe-retry guidance for writes
- Merge's own MCP server for the Unified API has been idle since 0.1.4 in April 2025
Price $650 / moAuth API keyx402 nohosted
Xero API + MCP
B 67.2/100Accounting API for Xero organisations, with contacts, invoices, bills, payments, bank transactions, manual journals, the balance sheet, profit and loss and trial balance, plus payroll in some regions.
Verdict Granular OAuth scopes, such as accounting.reports.profitandloss.read, required for apps created from 29 April 2026. Developer docs, including the per-minute rate limits, only render with JavaScript.
Choose it for An agent keeping the books for UK, Australian or New Zealand businesses, or any team that wants read-only scopes and long deprecation notice.
Strengths
- Granular OAuth scopes, such as accounting.reports.profitandloss.read, required for apps created from 29 April 2026
- Deprecations announced with 12 to 13 months' notice on a dated changelog
- Public OpenAPI specs, with an Idempotency-Key parameter on 101 accounting operations
Weaknesses
- Developer docs, including the per-minute rate limits, only render with JavaScript
- 1,000 calls a day per organisation on the free tier, 5,000 on paid
- Official MCP server idle since 5 June 2026, with no CI, no annotations and no registry entry
Price FreemiumAuth OAuthx402 nohosted and local
Pennylane
B 66.3/100Pennylane is a French accounting and invoicing platform for companies and accounting firms. Its Company and Firm REST APIs cover invoices, supplier invoices, ledger entries, transactions and exports. A hosted read-only MCP server exposes the same books to AI assistants.
Verdict The v2 API has per-resource read and write scopes, an OpenAPI definition on every reference page, llms.txt and a breaking-change process that ran over 24 weeks. Access needs a paid Essentiel plan or partner approval, creation endpoints are not idempotent, and the API agreement lets Pennylane change or revoke the API without notice.
Choose it for An agent working on the books of French companies or an accounting firm's client portfolio, with French chart of accounts, FEC export, Factur-X e-invoicing and VAT returns.
Strengths
- Scopes split each resource into
:readonlyand:all, for company tokens, firm tokens and OAuth apps - Hosted MCP server at
https://mcp.pennylane.com/mcpwith 31 read-only tools, OAuth 2.1 with PKCE and dynamic client registration - OpenAPI 3.0.1 definitions on each reference page, an llms.txt index and Markdown twins of every docs page
Weaknesses
- The API agreement allows changes, suspension or revocation with or without notice and supplies the API as is
- Creation endpoints do not enforce idempotency, except supplier invoice imports
- API and MCP access for companies starts at the Essentiel plan, and OAuth apps need approval from the Partnerships team
Price PaidAuth OAuth or keyx402 nohosted
Codat
B 64.3/100Codat connects a business's accounting, banking and commerce software to financial products and banks through one REST API. Product APIs cover bill pay, expenses, bank feeds and lending data, with official SDKs for TypeScript, Python and C#.
Verdict Public OpenAPI specs, an Idempotency-Key header on writes, Retry-After on 429 and a written three-month deprecation notice suit an agent that retries. Access is the limitation. No price or self-serve signup is published, the general Accounting API is closed to new clients, and API keys carry no scopes.
Choose it for Banks, lenders, bill pay, expense and card products that already have or will sign a Codat contract and need writes into many accounting packages.
Strengths
- Public OpenAPI 3 specs for every API in codatio/oas, with long operation descriptions and per-integration response examples
- Idempotency-Key header on POST and PATCH, cached for 90 minutes, and released after a 429 so the same key can be retried
- 429 responses carry Retry-After, and every response carries X-Rate-Limit-Limit, Remaining and Reset headers
Weaknesses
- No public price. The pricing page returns 404 and fees are set in an order form
- No self-serve signup found. The docs and the site ask new users to get in touch
- The general Accounting API spec says it is relevant only to existing clients, and the status page labels it Legacy
Price PaidAuth API keyx402 nohosted
Zoho Books
C 61.1/100Zoho Books is hosted accounting software from Zoho for small and mid-sized businesses. Agents reach it through the REST API v3, covering invoices, bills, payments, banking, journals and the chart of accounts behind OAuth 2.0.
Verdict The public OpenAPI files cover 885 operations with OAuth scopes per module and operation, and the Free plan allows 1,000 API requests a day. No report endpoint, official SDK, SLA or dated API changelog was found, and the documented token calls put the client secret in the URL.
Choose it for Small businesses already on Zoho that want an agent to raise invoices, record bills and payments, reconcile bank transactions and post journals with narrow scopes.
Strengths
- OpenAPI 3.0.0 files for 45 resources and 885 operations download from the docs as
openapi-all.zip - OAuth scopes narrow to one module and one operation, such as
ZohoBooks.invoices.READ - Every API reference operation has a Markdown twin, such as
/books/api/v3/invoices/create-an-invoice.md
Weaknesses
- No profit and loss, balance sheet or other report endpoint appears in the API docs or the OpenAPI files
- The documented token and refresh calls put the client secret and refresh token in the URL query string
- Daily caps are low, 1,000 requests on Free and 10,000 on the top three plans
Price $15 / moAuth OAuthx402 nohosted
FreeAgent API
C 57.2/100REST API for FreeAgent, the UK small-business accounting product owned by NatWest Group.
Verdict Published limits of 120 requests a minute and 3,600 an hour per user, with Retry-After on 429. No OAuth scopes, so a token can do anything the authorising user can.
Choose it for An agent doing the books for a UK freelancer or small limited company, especially one already banking with NatWest.
Strengths
- Published limits of 120 requests a minute and 3,600 an hour per user, with Retry-After on 429
- X-RateLimit-Test header that lowers the sandbox to 5 requests a minute for testing back-off
- API free under section 4.1 of the terms, with 30 days' notice before any fee
Weaknesses
- No OAuth scopes, so a token can do anything the authorising user can
- No OpenAPI spec, SDK, llms.txt or official MCP server
- Error responses aren't documented beyond the 429
Price Your planAuth OAuthx402 nohosted
Odoo External API
C 55.9/100Odoo is a business suite from Odoo SA in Belgium with accounting, invoicing, sales, stock and HR apps on one database. Outside software reaches it through the JSON-2 HTTP API with API keys and, from Odoo 20, an MCP server.
Verdict One endpoint pattern reaches every model, with field selection, filters and paging, and keys that expire within three months. On Odoo Online the external API needs the Custom plan, there is no OpenAPI file, and the acceptable use policy asks for about one call a second with no parallel calls.
Choose it for An agent working inside a company that already runs Odoo, where invoices, bills, journal entries, stock and sales sit in one database behind one endpoint pattern.
Strengths
/json/2/<model>/<method>reaches every model the user can see, includingaccount.movefor invoices, bills and journal entries- API keys are per user, shown once, expire within three months at most and can be generated and revoked through the API
- Odoo 20 adds an MCP server at
<database_url>/mcpthat exposes five read-only tools by default, with write tools switched on one by one
Weaknesses
- On Odoo Online the external API is limited to the Custom plan. One App Free and Standard exclude it
- No OpenAPI file and no llms.txt. The per-database reference at
/docneeds a login or a key, and its docs section reads "Under construction" - The acceptable use policy puts API traffic at about one call a second with no parallel calls. No 429 or Retry-After handling was found in the docs
Price PaidAuth API keyx402 nolocal
Rutter Accounting API
C 55.6/100Unified API for accounting, commerce and payment platforms, aimed at lenders and financial software developers.
Verdict Idempotency-Key header on writes, and prefer_sync writes that fall back to async after 30 seconds. Production prices are quote-only.
Choose it for Lenders, spend-management and fintech products that read ledgers alongside commerce and payment platforms, and that need writes an agent can retry safely.
Strengths
- Idempotency-Key header on writes, and prefer_sync writes that fall back to async after 30 seconds
- Error codes 450, 451, 452 and 550 that separate the platform's failure from Rutter's
- OpenAPI spec per dated API version, with an upgrade guide listing breaking changes
Weaknesses
- Production prices are quote-only
- Terms and privacy policy are Google Drive PDFs, and no legal entity is named on the site
- The per-connection access_token travels as a URL query parameter
Price PaidAuth API keyx402 nohosted
Invoice Ninja API
D 52.1/100Source-available invoicing platform (Laravel) you can self-host or use hosted at invoicing.co.
Verdict OpenAPI 3 spec with 379 operations and curl and PHP examples on each path. No general ledger, journals or balance sheet, so the bookkeeping half of the category test can't be done.
Choose it for An agent that quotes, invoices, chases and records payments for a small business, or for anyone who wants the billing system on their own server.
Strengths
- OpenAPI 3 spec with 379 operations and curl and PHP examples on each path
- Public demo endpoint with the token TOKEN, no account needed
- Self-hosting is free with every Pro and Enterprise feature
Weaknesses
- No general ledger, journals or balance sheet, so the bookkeeping half of the category test can't be done
- Rate limits aren't in the docs, only in the source
- Status page shows seven days and has no history page
Price $14 / moAuth API keyx402 nohosted
Head to head
- Apideck Accounting API + MCP vs Merge Accounting API BB 72.9 vs BB 70
- Apideck Accounting API + MCP vs Xero API + MCP BB 72.9 vs B 67.2
- Apideck Accounting API + MCP vs Pennylane BB 72.9 vs B 66.3
- Apideck Accounting API + MCP vs Codat BB 72.9 vs B 64.3
- Merge Accounting API vs Xero API + MCP BB 70 vs B 67.2
- Merge Accounting API vs Pennylane BB 70 vs B 66.3
- Codat vs Merge Accounting API B 64.3 vs BB 70
- Pennylane vs Xero API + MCP B 66.3 vs B 67.2
- Codat vs Xero API + MCP B 64.3 vs B 67.2
- Codat vs Pennylane B 64.3 vs B 66.3
Questions
What are the highest-rated accounting and invoicing APIs for AI agents?
Apideck Accounting API + MCP has the highest benchmark score of the 12 ranked accounting and invoicing APIs, 72.9 (BB). Merge Accounting API is second with 70 (BB).
How many accounting and invoicing APIs are agent-ready?
2 of the 12 ranked here grade BB or better, the bar for agent-ready on the Anchor benchmark.
Which accounting and invoicing APIs accept x402 payments?
None of the ranked listings here accepts x402 for its main call yet.
How is this list ranked?
By the Anchor benchmark score out of 100, a weighted mean of the scored categories minus deductions for negative events, from public evidence re-checked as vendors change. Listings cannot pay for a place. The latest assessment behind this page is from 9 October 2026.
How this list is made
The order is the Anchor benchmark score, the same number as on each listing and in the top list. Each listing is graded from public evidence against the benchmark checklist, and the picks above are worked out from those grades, prices and facts. No listing pays for its place, and paid audits or listing help never change a score.
Full ranked table · 66 head-to-head comparisons · Best tools in every category