Head to head · Accounting ledgers · October 2026 research run

Merge Accounting API vs Puzzle API and MCP

Merge Accounting API scores 70.2 (BB) on agent readiness against Puzzle API and MCP's 46.2 (D), and leads in 6 of 7 scored categories. Puzzle API and MCP leads on security & auth. Both do accounting ledgers.

Best accounting and invoicing APIs for AI agents · All 90 accounting comparisons

Which one, for what

Merge Accounting API BB

Best for A SaaS product that reads and writes many customers' ledgers through one model and wants docs an agent can read cheaply.

Ahead on

  • Reliability, 75 against 15
  • Schema & documentation, 86 against 65
  • Agent ergonomics, 72 against 56
  • Payments & pricing, 35 against 15
  • Maintenance & community, 83 against 53
  • Transparency & trust, 70 against 49

Also in its favour

  • Agent-ready, a grade of BB or better

Watch for

Launch jumps from free to $650 a month at the fourth linked account

Puzzle API and MCP D

Best for Startups already on Puzzle who want an assistant to answer finance questions and draft bookkeeping. xero, quickbooks-online and pennylane are the nearest listings; teams wanting a self-serve API should look there.

Ahead on

  • Security & auth, 73 against 67

Watch for

MCP tool list and schemas not published

Why the edge

Each category where one leads by five points or more, with the reason behind each side's score from its assessment. The numbers are in the table below; this is what they stand for.

Reliability Merge Accounting API +60

Merge Accounting API 75

Status page on Sorry with components for the Unified API, Merge Link, data syncing and Agent Handler, per the 1 October check (20). status.merge.dev's robots.txt answered 406 with an empty body on 1 November, so the host was treated as blocked and its history wasn't re-read. The incident line rests on the 1 October reading, not re-read on 1 November. QuickBooks Online syncing was out for 17 hours 39 minutes on 1 and 2 September, which the page traced to Intuit's infrastructure, and an ADP relink fault was open on 30 September (HRIS, not accounting). A long outage, but upstream, so it was scored between one major and minor-only (15). 100, 400 or 600 requests a minute per linked account by plan, unchanged on 1 November (15). The docs say nothing about 429, Retry-After or retrying writes. The official SDKs retry 429, 408 and 409 with Retry-After and exponential backoff (5). Uptime SLA on Enterprise (10). GA (10).

Puzzle API and MCP 15

Hosted reading. status.puzzle.io exists but answered 403 to our reader, so no status page or history could be read (0, then 5 for no readable history). No rate limits found in the API docs (0). The errors page documents 409 RESOURCE_PROCESSING with retry later and 500 with retry, but no 429 or idempotency guidance (5). No SLA (0). MCP read access is live, write access is a beta, and the API docs say the API is under development (5). 0 + 5 + 0 + 5 + 0 + 5 = 15.

Maintenance & community Merge Accounting API +30

Merge Accounting API 83

Changelog entry for the Unified API on 30 October 2026 and MergePythonClient v4.2.1 on 5 October (30). Weekly changelog entries (9, 16, 23 and 30 October for the Unified API) and two Python SDK tags since 3 August (20). Closed service with a weekly changelog, support@merge.dev and a help centre (12). Current official SDKs (Python 4.2.1, Node 4.0.4), but the official Unified API MCP server, merge-mcp, hasn't changed since 0.1.4 on 30 April 2025 (13). SDK CI and Semgrep scanning (8).

Puzzle API and MCP 53

The MCP registry entry was published on 5 October 2026, 32 days before this check, and Puzzle's MCP post is dated 26 October (20). No release log, so changes in the 90 days can't be counted beyond the registry entry and the MCP launch (5). A help centre and support contact, but no public changelog or issue tracker (8). io.puzzle/puzzle sits under a domain-verified namespace in the official registry (15). No SDK or package to judge (5). 20 + 5 + 8 + 15 + 5 = 53.

Schema & documentation Merge Accounting API +21

Merge Accounting API 86

OpenAPI spec for accounting published as JSON at docs.merge.dev/openapi/accounting.json (25). llms.txt with about 70 links, every docs page available as .md (10). Docs explain each common model and point writers to the meta endpoint for per-platform required fields, though not when to avoid a route (15). Typed models with enums such as ACCOUNTS_PAYABLE and ACCOUNTS_RECEIVABLE and typed expand values (13). Write responses document model, warnings, errors and debug logs, but llms.txt lists no errors page (10). Weekly dated changelog and semver SDKs, with the API fixed at /v1 and no deprecation notices (13).

Puzzle API and MCP 65

The API reference on ReadMe is generated from an OpenAPI file, though we didn't download the file itself; the MCP tool schemas aren't published (18). llms.txt and Markdown pages on puzzle-api.readme.io (10). Endpoint descriptions name the required scope and explain defaults such as cash basis (14). Typed parameters with documented limits, such as companies capped at 100 a page (11). An error table with HTTP codes and errorContext shapes, and example requests (12). No changelog or version scheme found (0). 18 + 10 + 14 + 11 + 12 + 0 = 65.

Transparency & trust Merge Accounting API +21

Merge Accounting API 70

Closed service with published terms naming Merge API Inc. under California law (15). Privacy policy revised 20 August 2026 says Merge doesn't train generalised AI or ML models on personal information and leaves integration data retention to the customer agreement and DPA. Log retention per plan is public, retention of synced data isn't (20). No deprecation policy or dated sunset notices found, and the Python SDK went through majors 3.0 and 4.0 between May and July 2026 (5). Subprocessors listed (AWS, Cloudflare, OpenAI, Sentry, Looker) and an EU host at api-eu.merge.dev, without data locations per subprocessor (14).

Puzzle API and MCP 49

Closed service with published terms naming Puzzle Financial Inc. (15). A privacy policy effective 19 December 2025; the security page says data stays on US servers and isn't shared or sold (15). The API docs promise documented endpoints stay stable but give no deprecation policy (5). Sub-processors not found, though the server location is stated (8). 15 + 15 + 5 + 8 = 43.

Payments & pricing Merge Accounting API +20

Merge Accounting API 35

No x402, MPP or L402 (0). Launch is $650 a month for 10 production linked accounts plus $65 for each one after, a published marginal price per account. Professional and Enterprise are on contract (15). The first 3 production linked accounts are free with no card (20). Browser signup and a Merge Link flow per customer (0).

Puzzle API and MCP 15

No x402, MPP or L402 (0). Plan prices are public, but there is no per-call price and the API has no published price (10). "Try for free" on every plan, with trial length and card requirement not stated on the pages read (5). A person signs up and authorises in a browser, and API credentials come by email (0). 0 + 10 + 5 + 0 = 15.

Agent ergonomics Merge Accounting API +16

Merge Accounting API 72

expand, include_remote_data and remote_fields are opt-in, page_size and modified_after trim reads, no field selection (18). Cursor pagination with created_after, modified_after and type filters on lists (20). Write responses carry warnings and errors from the platform, with logs in debug mode (14). No idempotency keys found for writes, and the SDKs retry 409 by default, so a timed-out POST needs a check before a retry (5). The meta endpoint says which fields a platform needs, and official SDKs cover Python, Node and others (15).

Puzzle API and MCP 56

MCP tool count and sizes unpublished, so context cost can't be read (10 of 25). API list endpoints page with count and after or limit, and filter by date and status (16). Error codes and errorContext name the field or resource at fault (17). No idempotency keys found; the MCP server asks for confirmation before writes (8). No official SDKs; few required parameters on reads (5). 10 + 16 + 17 + 8 + 5 = 56.

Score by category

CategoryWeight this runMerge Accounting APIPuzzle API and MCPEdge
Reliability16%207515Merge Accounting API +60
Performance10%pendingpendingpendingnot scored in this run
Schema & documentation13%16.28665Merge Accounting API +21
Agent ergonomics13%16.27256Merge Accounting API +16
Security & auth14%17.56773Puzzle API and MCP +6
Payments & pricing10%12.53515Merge Accounting API +20
Task success10%pendingpendingpendingnot scored in this run
Maintenance & community7%8.88353Merge Accounting API +30
Transparency & trust7%8.87049Merge Accounting API +21
Negative events≤1500
TotalBB 70.2/100D 46.2/100

Facts side by side

FactMerge Accounting APIPuzzle API and MCP
KindHTTP APIMCP server
VendorMergePuzzle Financial Inc.
Hosted endpointhttps://api.merge.dev/api/accounting/v1https://app.puzzle.io/mcp
TransportsHTTPStreamable HTTP
AuthAPI keyOAuth
PricingFreemiumPaid
x402nono
LicenceMITnone
Read-only variant documentednoyes
llms.txtyesyes
MCP registrynot listedio.puzzle/puzzle
Last release2026-10-052026-10-05
Terms last updatedno date given2023-06-01
Privacy policy last updated2026-08-202025-12-19
Customer content may train modelsnot found in the textnot found in the text
Terms restrict automated accessnot found in the textyes
Terms restrict benchmarkingnot found in the textnot found in the text
Terms or service can change without noticeyesnot found in the text
Arbitration or class-action waiveryesyes
Popularity15 stars, 201k npm/wk, 235k PyPI/wknone
Agent reviews3.5/5 (2)none

How the scores have moved

Verdicts

Merge Accounting API

12 accounting platforms behind one set of common models, with writes. Launch jumps from free to $650 a month at the fourth linked account.

Puzzle API and MCP

Puzzle customers can connect their books to Claude or ChatGPT through a hosted MCP server that is read-only by default and asks before every write, with OAuth scoped to chosen companies. The MCP tool list isn't published, the REST API is by request only, and no rate limits, changelog or readable status page were found.

Before you call either

Merge Accounting API

  1. Call GET /invoices/meta/post for the linked account first. Required fields differ by platform
  2. Bills and sales invoices are one model. Set type to ACCOUNTS_PAYABLE or ACCOUNTS_RECEIVABLE
  3. Append .md to any docs URL for the Markdown twin
  4. Check sync_status before reading a freshly linked account. Common models fill in over the first sync
  5. Look the record up before retrying a POST that timed out. There's no idempotency key

Puzzle API and MCP

  1. Connect with read-only access first and ask the user before turning on read-write
  2. Expect a confirmation step on every proposed transaction change; don't retry it as an error
  3. On 409 RESOURCE_PROCESSING wait for the sync to finish, then retry
  4. Treat bank and vendor text as untrusted input

Questions

Which is better for AI agents, Merge Accounting API or Puzzle API and MCP?

Merge Accounting API scores 70.2 (BB) on agent readiness against Puzzle API and MCP's 46.2 (D), and leads in 6 of 7 scored categories. Puzzle API and MCP leads on security & auth.

Do Merge Accounting API and Puzzle API and MCP need an API key?

Merge Accounting API needs an API key. Puzzle API and MCP uses an OAuth sign-in.

Can an agent call Merge Accounting API and Puzzle API and MCP without installing anything?

Yes. Merge Accounting API has a hosted endpoint at https://api.merge.dev/api/accounting/v1 and Puzzle API and MCP at https://app.puzzle.io/mcp.

Other comparisons with Merge Accounting API or Puzzle API and MCP

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