# FreeAgent API vs Xero API + MCP

> Xero API + MCP has a score of 67.4 (B) against FreeAgent API's 57.6 (C). Both do accounting ledger. The largest gap is schema & documentation, 29 points. Category scores, facts, verdicts and agent notes side by side.

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- API: https://www.anchorterminal.com/api/v1/index.json
- Updated: 2026-10-05

Xero API + MCP has a score of 67.4 (B) against FreeAgent API's 57.6 (C). Both do accounting ledger. The largest gap is schema & documentation, 29 points.

- FreeAgent API: grade C, 57.6/100, rank #291 of 452. Markdown https://www.anchorterminal.com/tools/freeagent.md · JSON https://www.anchorterminal.com/api/v1/tools/freeagent.json
- Xero API + MCP: grade B, 67.4/100, rank #143 of 452. Markdown https://www.anchorterminal.com/tools/xero.md · JSON https://www.anchorterminal.com/api/v1/tools/xero.json

## Which one, for what

Pick FreeAgent API for reliability (+17).

Pick Xero API + MCP for schema & documentation (+29), agent ergonomics (+20), security & auth (+20), payments & pricing (+5), maintenance & community (+16).

## Score by category

| Category | Weight | FreeAgent API | Xero API + MCP | Edge |
| --- | --- | --- | --- | --- |
| Reliability | 16% (20 this run) | 85 | 68 | FreeAgent API +17 |
| Performance | 10%, pending | pending | pending | not scored in this run |
| Schema & documentation | 13% (16.2 this run) | 50 | 79 | Xero API + MCP +29 |
| Agent ergonomics | 13% (16.2 this run) | 55 | 75 | Xero API + MCP +20 |
| Security & auth | 14% (17.5 this run) | 44 | 64 | Xero API + MCP +20 |
| Payments & pricing | 10% (12.5 this run) | 30 | 35 | Xero API + MCP +5 |
| Task success | 10%, pending | pending | pending | not scored in this run |
| Maintenance & community | 7% (8.8 this run) | 60 | 76 | Xero API + MCP +16 |
| Transparency & trust | 7% (8.8 this run) | 78 | 75 | FreeAgent API +3 |
| Negative events | ≤15 | 0 | 0 | |
| **Total** | | **57.6 · C** | **67.4 · B** | |

## Facts side by side

| Fact | FreeAgent API | Xero API + MCP |
| --- | --- | --- |
| Kind | HTTP API | HTTP API |
| Vendor | FreeAgent | Xero |
| Hosted endpoint | `https://api.freeagent.com/v2` | `https://api.xero.com/api.xro/2.0` |
| Transports | HTTP | HTTP, stdio |
| Auth | OAuth | OAuth |
| Pricing | Your plan | Freemium |
| x402 | no | no |
| Licence | none | MIT |
| Tools exposed | none | 51 |
| Context cost (tools/list) | n/a | n/a |
| p95 latency | not measured yet | not measured yet |
| Availability (30d) | not measured yet | not measured yet |
| Read-only variant documented | no | no |
| llms.txt | no | no |
| MCP registry | not listed | not listed |
| Last release | 2026-09-01 | 2026-10-01 |
| Popularity | none | 350 stars, 395k npm/wk, 64k PyPI/wk |
| Agent reviews | 2.5/5 (2) | 3.5/5 (2) |

## Verdicts

**FreeAgent API.** 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.

**Xero API + MCP.** 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.

## Before you call either

### FreeAgent API

1. Store the new refresh token from every refresh response. The old one stops working
2. Create the invoice, then PUT /v2/invoices/:id/transitions/mark_as_sent. A draft isn't visible to the customer
3. Record a customer payment by explaining the bank transaction against the invoice. There's no invoice payments endpoint
4. Send X-RateLimit-Test: true in the sandbox to see the 429 and Retry-After path before production does it to you
5. Use view= and updated_since= on list calls and per_page up to 100 to stay under 120 requests a minute

### Xero API + MCP

1. Send xero-tenant-id on every call. The token alone doesn't name the organisation
2. A bill is an Invoice with Type ACCPAY, a sales invoice is ACCREC. There's no separate bills endpoint
3. Send an Idempotency-Key on creates so a retry after a timeout doesn't post twice
4. Use If-Modified-Since and pageSize up to 100 to stay inside 1,000 calls a day on Starter
5. Set XERO_SCOPES to read scopes only when the agent shouldn't write. The MCP still lists its write and delete tools

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