Numeral vs TaxCloud

Numeral

Docs are written for agents, with a public OpenAPI spec for 32 operations, Markdown pages, llms.txt and a remote MCP server whose 14 tools are read-only by default. No status page, numeric rate limit or SLA was found, the API ignores idempotency keys, and API access is sold on a custom plan after a demo.

TaxCloud

A 30-operation REST API with a public OpenAPI 3.1 contract, llms.txt, Markdown docs and a 30-day trial that needs no card. The vendor publishes no rate limit numbers, no SLA, no API changelog and no official v3 client library, and the security page names no audit or certification.

Numeral

1. Send X-API-Version: 2026-03-01 on every call to https://api.numeralhq.com. Merchant, platform and certificate endpoints reject requests without it
2. Commit with a stable reference_order_id. On REFERENCE_ORDER_ID_ALREADY_EXISTS look up the existing transaction, because Idempotency-Key is ignored
3. Commit before the calculation's expires_at. If it has expired, calculate again and commit the new calculation_id with the original reference_order_id
4. Send amount as the line total in minor units to /tax/calculations and as the per-unit price to /tax/platform/calculations
5. Start with an sk_test_ key. Certificate endpoints and MCP certificate tools are live only and answer TESTMODE_NOT_SUPPORTED or live_mode_required

TaxCloud

1. Send X-API-KEY on every call and put the connection ID in the path, as in /tax/connections/{connectionId}/carts. A wrong ID returns 404
2. Mark nexus states active in the account first. With none active the API returns zero tax and no error
3. Use a separate test connection. There is no sandbox, and orders on a live connection go into filing
4. Pass a stable idempotencyKey on refunds, and never convert the same cart twice. A second conversion creates a duplicate liability
5. Void a wrong order before 12:00 AM Eastern on the 10th of the month after its completedDate. Later requests return 422