OpenSalesTax vs Zamp

OpenSalesTax is a free, self-hosted API that calculates sales tax for US transactions using public data and per-state modules. The project says its modules cover 52 jurisdictions, while each published data dump includes all 48 jurisdictions that impose sales tax. The API calculates tax on line items and can break results down by state, county, city, or district. Documented item categories include general goods, clothing, groceries, prescription drugs, prepared food, and digital goods. Its data comes from Streamlined Sales Tax files and state Department of Revenue publications, rather than paid tax feeds. The engine can be installed from source or run with Docker; PostgreSQL is the default, with optional MariaDB support. Access defaults to open with per-IP rate limiting, or can use API keys with per-key limits and usage tracking. Release dumps reflect the SST quarterly file current at release, and the project documents loading newer data. It identifies incomplete sub-state tax stacking for Colorado home-rule cities and Louisiana parish-level collectors. The project says its calculations are not legal or tax advice and advises checking results with the relevant state Department of Revenue before remitting.

Zamp has no write-up on Specifiction yet; its figures are above.