Check vs PayFit

Check

Graded as embedded payroll through a partner API key, not access to an existing employer's payroll account. The API has idempotency keys on writes, a required preview before approval and queryable request logs. No price is public, a sandbox key comes through Check's sales team, and one API key carries the whole partner account.

PayFit

A public OpenAPI 3.0 file, llms.txt and scoped keys let a paying customer's agent read payroll outputs and write absences. The API cannot run or approve a payroll, new partner integrations are not being accepted, and no idempotency keys or SDKs were found.

Check

1. Use https://sandbox.checkhq.com with the sandbox key and https://api.checkhq.com with the production key. A key is not valid across environments
2. Preview a payroll before approving it, then pass preview_started_at to POST /payrolls/{id}/approve so a stale preview fails with 409
3. Send X-Idempotency-Key on every write. Keys expire after 24 hours, so list the resource before retrying later than that
4. On 429 wait for Retry-After. The limit is 10 requests a second in sandbox and for partners paying fewer than 1,000 payees a month, with 100 concurrent requests
5. Connect the MCP server with ?read_only=true or X-MCP-Readonly: true unless writes are intended. In production, approving a payroll moves money

PayFit

1. Have a company admin create the key at app.payfit.com/integrations/hub/api with only the scopes the task needs. The key is shown once
2. POST the key to https://oauth.payfit.com/introspect to get company_id, then call https://partner-api.payfit.com/companies/{companyId}/...
3. Page lists with nextPageToken and maxResults, which defaults to 10 and stops at 50
4. Check before repeating a failed POST. There is no idempotency key, and POST /absences creates an absence that is already validated
5. A collaborator or contract created through the API stays incomplete until an HR admin finishes it in the PayFit app, and a new contract takes 2 to 5 minutes to appear