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Head to head · Spend transactions · October 2026 research run

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.

Mercury APIMercury Technologies, Inc. · HTTP API B63.8/100#337 of 841 Payhawk API + MCPPayhawk Limited · HTTP API C57.1/100#561 of 841

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

CategoryWeight this runMercury APIPayhawk API + MCPEdge
Reliability16%205958Mercury API +1
Performance10%pendingpendingpendingnot scored in this run
Schema & documentation13%16.27271Mercury API +1
Agent ergonomics13%16.26852Mercury API +16
Security & auth14%17.58271Mercury API +11
Payments & pricing10%12.53013Mercury API +17
Task success10%pendingpendingpendingnot scored in this run
Maintenance & community7%8.86453Mercury API +11
Transparency & trust7%8.86378Payhawk API + MCP +15
Negative events≤1500
Total63.8 · B57.1 · C

Facts side by side

FactMercury APIPayhawk API + MCP
KindHTTP APIHTTP API
VendorMercury Technologies, Inc.Payhawk Limited
Hosted endpointhttps://api.mercury.com/api/v1https://api.payhawk.com
TransportsHTTPHTTP
AuthOAuth or keyOAuth or key
PricingFreemiumPaid
x402nono
LicenceProprietary service under Mercury's Terms of Use. The Mercury CLI on GitHub is Apache-2.0Proprietary service under Payhawk's general terms and conditions
Tools exposed3582
Read-only variant documentedyesyes
llms.txtyesyes
Last release2026-08-122026-10-08
Terms last updatedno date given2025-12-09
Privacy policy last updatedno date given2026-06-29
Customer content may train modelsnot found in the textnot found in the text
Terms restrict automated accessyesnot found in the text
Terms restrict benchmarkingyesnot found in the text
Terms or service can change without noticenot found in the textnot found in the text
Arbitration or class-action waiveryesnot 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.

Other comparisons with Mercury API or Payhawk API + MCP

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