Quaderno vs TaxJar

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.

TaxJar

A 21-operation REST API with a no-card 30-day trial, caller-chosen transaction IDs that make order pushes safe to repeat, and no status-page incident since March 2026. No OpenAPI spec or llms.txt was found, the API changelog stops at January 2022, tokens carry no scopes, and calculation is US-only for new accounts.

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

TaxJar

1. Send x-api-version: 2022-01-24 on every call. Accounts opened before 3 February 2022 default to an older version with weaker validation
2. Pass nexus_addresses[] or keep nexus states in the account. Without nexus the API returns zero tax and reports no error
3. Create orders with your own transaction_id. On 422 the order already exists, so send a PUT to update it
4. Post JSON with Content-Type: application/json. Form-encoded arrays such as line_items[] can return 406
5. Cache calculations and skip states without nexus. Each calculation or rate lookup counts as a tenth of an order, errors included