TaxJar vs Zamp

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.

Zamp

A free 30-day sandbox key needs no card or sales call, and the docs are served as Markdown with llms.txt and a published limit of 1,000 requests a minute. There is no OpenAPI file, SDK, API changelog or published price, production keys come with a sales-led account, and the site footer says SOC 2 compliance is in progress.

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

Zamp

1. Call POST /calculations for a quote and POST /transactions only when the sale is final. Put the returned taxDue in taxCollected when posting
2. Keep transaction and line item ids to 25 characters. A repeated POST /transactions with an existing id returns 409 CONFLICT, so a retry doesn't create a second record
3. For a refund, post a new transaction with parentId set to the sale's id and a negative quantity. Never send a negative amount on a line item
4. Send shipToAddress.state and country set to CA for Canadian orders. POST /addresses validates US addresses only
5. Page lists with limit (1 to 100, default 10) and cursor until nextCursor is null. GET /transactions returns only transactions written with the same key
6. Don't store sensitive or personal data in the sandbox. Trial data is deleted after 30 days and the trial terms forbid live customer data