Avalara AvaTax vs TaxJar

Avalara AvaTax

The REST API has a public Swagger file with 491 operations, a Markdown page per endpoint and a 90-day trial with no card. Production rate limits and prices per transaction are not published, the API patch notes stop at April 2023, and the tax calculation service was degraded for about 23 hours on 5 and 6 October 2026.

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.

Avalara AvaTax

1. Omit type or send SalesOrder for an estimate. A type ending in Invoice is recorded, and commit set to true locks it for reporting
2. Retry a timed-out invoice with CreateOrAdjustTransaction, not CreateTransaction, which errors when a committed transaction has the same code
3. Use sandbox-rest.avatax.com with sandbox credentials for tests. Production is rest.avatax.com and the two accounts are separate
4. Add $include=SummaryOnly or LinesOnly to shrink transaction responses, and page lists with $top (1,000 at most) and $skip
5. Call /api/v2/utilities/ping first. It answers without credentials and shows whether the credentials sent were accepted

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