# Mercury API vs Payhawk API + MCP

> Mercury API scores 63.8 (B) on agent readiness against Payhawk API + MCP's 57.1 (C), and leads in 6 of 7 scored categories. Payhawk API + MCP leads on transparency & trust. Both do spend transactions. Category scores, facts, verdicts and agent notes side by side.

- Canonical: https://www.anchorterminal.com/compare/mercury-vs-payhawk
- Markdown: https://www.anchorterminal.com/compare/mercury-vs-payhawk.md (~2,200 tokens)
- Slim: https://www.anchorterminal.com/compare/mercury-vs-payhawk.min.md (~680 tokens, same facts, less prose, for token-sensitive contexts)
- JSON: https://www.anchorterminal.com/compare/mercury-vs-payhawk.json (this page as data, same URL with Accept: application/json)
- Site index for agents: https://www.anchorterminal.com/llms.txt (full text: https://www.anchorterminal.com/llms-full.txt)
- API: https://www.anchorterminal.com/api/v1/index.json
- Updated: 2026-10-09

Mercury API scores 63.8 (B) on agent readiness against Payhawk API + MCP's 57.1 (C), and leads in 6 of 7 scored categories. Payhawk API + MCP leads on transparency & trust. Both do spend transactions.

- Mercury API: grade B, 63.8/100, rank #337 of 842. Markdown https://www.anchorterminal.com/tools/mercury.md · JSON https://www.anchorterminal.com/api/v1/tools/mercury.json
- Payhawk API + MCP: grade C, 57.1/100, rank #561 of 842. Markdown https://www.anchorterminal.com/tools/payhawk.md · JSON https://www.anchorterminal.com/api/v1/tools/payhawk.json

## Which one, for what

### Mercury API (B)

Good for: A company that banks with Mercury and wants an agent to read balances and transactions, set notes and categories, upload receipts, issue virtual cards with spend limits and queue payments for human approval.

Ahead on:
- Agent ergonomics, 68 against 52
- Security & auth, 82 against 71
- Payments & pricing, 30 against 13
- Maintenance & community, 64 against 53

Watch for: No rate limits with numbers and no 429 handling were found in the reviewed documentation

### Payhawk API + MCP (C)

Good for: A finance team already on Payhawk that wants an ERP or accounting sync, master data kept in step, purchase orders raised from another system, or an assistant that answers spend questions and prepares approvals.

Ahead on:
- Transparency & trust, 78 against 63

Watch for: No self-serve route. The API needs a Payhawk customer account, and a development sandbox is requested through a form


## Score by category

| Category | Weight | Mercury API | Payhawk API + MCP | Edge |
| --- | --- | --- | --- | --- |
| Reliability | 16% (20 this run) | 59 | 58 | Mercury API +1 |
| Performance | 10%, pending | pending | pending | not scored in this run |
| Schema & documentation | 13% (16.2 this run) | 72 | 71 | Mercury API +1 |
| Agent ergonomics | 13% (16.2 this run) | 68 | 52 | Mercury API +16 |
| Security & auth | 14% (17.5 this run) | 82 | 71 | Mercury API +11 |
| Payments & pricing | 10% (12.5 this run) | 30 | 13 | Mercury API +17 |
| Task success | 10%, pending | pending | pending | not scored in this run |
| Maintenance & community | 7% (8.8 this run) | 64 | 53 | Mercury API +11 |
| Transparency & trust | 7% (8.8 this run) | 63 | 78 | Payhawk API + MCP +15 |
| Negative events | ≤15 | 0 | 0 | |
| **Total** | | **63.8 · B** | **57.1 · C** | |

## Facts side by side

| Fact | Mercury API | Payhawk API + MCP |
| --- | --- | --- |
| Kind | HTTP API | HTTP API |
| Vendor | Mercury Technologies, Inc. | Payhawk Limited |
| Hosted endpoint | `https://api.mercury.com/api/v1` | `https://api.payhawk.com` |
| Transports | HTTP | HTTP |
| Auth | OAuth or key | OAuth or key |
| Pricing | Freemium | Paid |
| x402 | no | no |
| Licence | Proprietary service under Mercury's Terms of Use. The Mercury CLI on GitHub is Apache-2.0 | Proprietary service under Payhawk's general terms and conditions |
| Tools exposed | 35 | 82 |
| Read-only variant documented | yes | yes |
| llms.txt | yes | yes |
| Last release | 2026-08-12 | 2026-10-08 |
| Terms last updated | no date given | 2025-12-09 |
| Privacy policy last updated | no date given | 2026-06-29 |
| Customer content may train models | not found in the text | not found in the text |
| Terms restrict automated access | yes | not found in the text |
| Terms restrict benchmarking | yes | not found in the text |
| Terms or service can change without notice | not found in the text | not found in the text |
| Arbitration or class-action waiver | yes | not found in the text |

## Verdicts

**Mercury API.** Custom tokens take per-endpoint scopes, write tokens need an IP allowlist, and payments can be queued for approval in the dashboard through `POST /account/{accountId}/request-send-money`. No rate limits, error catalogue or SLA were found in the reviewed documentation, the changelog carries no dates, and the MCP server is beta.

**Payhawk API + MCP.** The Developer API has a public OpenAPI 3.1 definition with 179 operations, read-only or full-access keys and a published limit of 15 requests a second. It needs a Payhawk customer account, no official SDK or API changelog was found, and the 82-tool MCP server is added by hand because it is not yet in the assistant directories.

## Before you call either

### Mercury API

1. Ask for a Custom token with only the scopes the task needs. Scopes can't be edited later, and a token unused for 45 days is deleted.
2. Without a fixed IP address, send payments through `POST /account/{accountId}/request-send-money`. Direct sends through `POST /account/{accountId}/transactions` need an allowlisted IP.
3. Send a stored `idempotencyKey` with every payment. The same recipient, account, amount and method within 24 hours returns 400 even with a new key.
4. Set `limit` on list calls. `GET /transactions` returns up to 1,000 rows by default.
5. Test against `https://api-sandbox.mercury.com/api/v1/` with a sandbox token. Webhooks aren't available in the sandbox.

### Payhawk API + MCP

1. Send the key in `X-Payhawk-ApiKey` or as a Bearer token to `https://api.payhawk.com/api/v3`. A read-only key returns 403 on writes
2. Page lists with `$skip` and `$take`. The help centre gives 1,000 a page and the definition a maximum of 10,000, so count what comes back
3. Pass `$filter` as URL-encoded JSON, for example `{"status":{"$equal":"draft"}}`. Date filters compare the date part only
4. Keep to 15 requests a second and wait for `Retry-After` on a 429. Do not send `Idempotency-Key` when creating a per diem expense, which returns 400
5. Use a group-level key and the `/groups/{groupId}` paths for master data in a multi-entity group. Expenses and payments stay on account paths

## Questions

### Which is better for AI agents, Mercury API or Payhawk API + MCP?

Mercury API scores 63.8 (B) on agent readiness against Payhawk API + MCP's 57.1 (C), and leads in 6 of 7 scored categories. Payhawk API + MCP leads on transparency & trust.

### Do Mercury API and Payhawk API + MCP need an API key?

Both take an API key or an OAuth sign-in.

### Can an agent call Mercury API and Payhawk API + MCP without installing anything?

Yes. Mercury API has a hosted endpoint at https://api.mercury.com/api/v1 and Payhawk API + MCP at https://api.payhawk.com.


## For agents

- This comparison as JSON: https://www.anchorterminal.com/compare/mercury-vs-payhawk.json, and with the fewest tokens: https://www.anchorterminal.com/compare/mercury-vs-payhawk.min.md
- Over MCP at https://www.anchorterminal.com/mcp (no key): `compare_tools {"a": "mercury", "b": "payhawk"}`. From a terminal: `anchor compare mercury payhawk`
- Each listing in full: https://www.anchorterminal.com/api/v1/tools/mercury.json and https://www.anchorterminal.com/api/v1/tools/payhawk.json

## Other comparisons with Mercury API or Payhawk API + MCP

- [Airwallex Spend and Issuing vs Mercury API](https://www.anchorterminal.com/compare/airwallex-vs-mercury.md)
- [Airwallex Spend and Issuing vs Payhawk API + MCP](https://www.anchorterminal.com/compare/airwallex-vs-payhawk.md)
- [BILL vs Mercury API](https://www.anchorterminal.com/compare/bill-vs-mercury.md)
- [BILL vs Payhawk API + MCP](https://www.anchorterminal.com/compare/bill-vs-payhawk.md)
- [Brex vs Mercury API](https://www.anchorterminal.com/compare/brex-vs-mercury.md)
- [Brex vs Payhawk API + MCP](https://www.anchorterminal.com/compare/brex-vs-payhawk.md)
- [Expensify vs Mercury API](https://www.anchorterminal.com/compare/expensify-vs-mercury.md)
- [Expensify vs Payhawk API + MCP](https://www.anchorterminal.com/compare/expensify-vs-payhawk.md)
- [Mercury API vs Pleo API + MCP](https://www.anchorterminal.com/compare/mercury-vs-pleo.md)
- [Mercury API vs Ramp](https://www.anchorterminal.com/compare/mercury-vs-ramp.md)
- [Mercury API vs Spendesk API + MCP](https://www.anchorterminal.com/compare/mercury-vs-spendesk.md)
- [Payhawk API + MCP vs Pleo API + MCP](https://www.anchorterminal.com/compare/payhawk-vs-pleo.md)
- [Payhawk API + MCP vs Ramp](https://www.anchorterminal.com/compare/payhawk-vs-ramp.md)
- [Payhawk API + MCP vs Spendesk API + MCP](https://www.anchorterminal.com/compare/payhawk-vs-spendesk.md)