TaxCloud vs TaxJar

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.

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.

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

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