Expensify vs Payhawk API + MCP

Expensify

One endpoint exports reports through caller-written templates and creates expenses, reports, rules and workspace settings, with limits of 5 requests per 10 seconds published and a status page that tracks the API separately. There is no OpenAPI spec, changelog, SDK, pagination or idempotency key, and one credential pair carries the whole account's rights.

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.

Expensify

1. POST requestJobDescription as a form field to the single endpoint. Keep it out of the URL query string, because it carries the secret
2. Read responseCode in the body on every reply. HTTP status can be 200 on failure, and validation errors use 410
3. Stay under 5 requests per 10 seconds and 20 per 60 seconds. No Retry-After header is documented, so space retries yourself
4. Export in two calls. A file job returns a filename, then a download job fetches it. Amounts are in cents
5. Don't retry a create job blindly. No idempotency key exists, so export and check before resending. Set dry-run to true when testing the Advanced Employee Updater

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