Numeral vs Quaderno

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.

Quaderno

A public OpenAPI 3.1 spec covers 92 operations, with a free sandbox and a status page showing no incident since July 2025. The API key has full account access, there are no idempotency keys, and the newest public API version is dated October 2024.

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

Quaderno

1. Call GET https://quadernoapp.com/api/authorization first. Its href gives the account subdomain that every other call needs
2. Before retrying a failed POST /transactions, list invoices by processor_id to check whether the sale was recorded. There is no idempotency key
3. Treat GET /invoices/{id}/deliver as a write. It emails the invoice to the customer
4. Correct a final invoice with a credit note. DELETE on invoices returns 410 and PUT accepts only notes, tags, metadata and address fields
5. Read X-RateLimit-Remaining and X-RateLimit-Reset, and page with created_before and limit up to 100