OpenSalesTax

OpenSalesTax is a free, self-hosted API for calculating sales tax on US transactions. It uses public data organized into per-state modules, which the project says cover 52 jurisdictions; each published data dump includes all 48 jurisdictions that impose sales tax. The API calculates tax for line items and can return results by state, county, city, or district. Documented item categories include general goods, clothing, groceries, prescription drugs, prepared food, and digital goods. The project uses Streamlined Sales Tax files and state Department of Revenue publications, rather than paid tax data feeds. You can install the engine from source or run it with Docker. PostgreSQL is required by default, with MariaDB available as an optional extra. Access defaults to open access with per-IP rate limits; API-key mode uses an X-API-Key header and supports per-key limits and usage tracking. Release dumps are based on the SST quarterly file current at release, and the project documents how to fetch and load newer source data. The project notes incomplete sub-state tax stacking for Colorado home-rule cities and Louisiana parish-level collectors. Its calculations are not legal or tax advice; it advises checking results with the relevant state Department of Revenue before remitting. It is pre-1.0, and its public users registry lists no self-hosters or integrators.

OpenSalesTax provides a self-hosted API with jurisdiction-level breakdowns and documented data refresh steps. Users should account for its listed coverage gaps and verify calculations with the relevant state Department of Revenue before remitting.

OpenSalesTax may suit developers or organizations seeking a self-hosted API for US sales-tax calculations using public data. Its database and sub-state coverage limitations matter for teams evaluating deployment and results.

OpenSalesTax is a free, self-hosted API for calculating U.S. sales tax from public data. It suits developers and small teams that can operate a database and maintain tax-data updates. The zero-cost, open-source model is attractive for a focused engine, while documented local-jurisdiction gaps rule it out for coverage-critical compliance.

Overview

OpenSalesTax calculates tax on individual line items and can return a jurisdictional breakdown by state, county, city, or district. Its scope is sales tax rather than a broader filing, remittance, or audit service, and the project says its output is not legal or tax advice. Businesses remain responsible for checking results with the relevant state Department of Revenue before remitting.

The project describes modules for 52 jurisdictions, with every one of the 48 sales-taxing jurisdictions loaded into each published data dump. It uses Streamlined Sales Tax files and state Department of Revenue publications instead of paid tax-data feeds. That keeps the system independently deployable, but public inputs do not resolve the stated incomplete sub-state tax stacking for Colorado home-rule cities or parish-level collectors in Louisiana.

Key features

Line-item calculation and categories

Documented categories include general goods, clothing, groceries, prescription drugs, prepared food, and digital goods. This gives developers a practical way to pass product context into calculations instead of applying one blanket rate. Teams selling products outside those categories should confirm that their classification approach produces the treatment they need.

Jurisdiction detail

Responses can separate state, county, city, and district amounts. That level of detail is useful when invoices, reporting, or internal reconciliation need to show how a total was assembled, although the Colorado and Louisiana coverage caveats matter for businesses operating in those local systems.

Deployment and controls

You can install from source or run the engine with Docker. PostgreSQL is the default database, while MariaDB support is an optional extra, so this is best for teams already comfortable running relational infrastructure. The Docker runtime image does not include the psql client; restoring data in the container therefore fails until that package is added, or the source-install route is used.

Authentication is open by default and rate-limited per IP. An API-key mode accepts an X-API-Key header and adds per-key rate limits and usage tracking, giving a more accountable setup for production integrations than the default access model.

Data maintenance

Release dumps are pinned to the Streamlined Sales Tax quarterly file current at release. Documentation explains how to fetch and load newer source data, which helps teams establish a refresh process but also makes ongoing maintenance part of ownership rather than a managed service.

Pricing

Free / open source — free. The Apache 2.0, self-hostable plan includes the U.S. sales-tax calculation API with no subscription charge. It is the right fit for developers who can provide hosting, database operations, rate monitoring, and data-refresh work. The trade-off is that there is no managed vendor layer described for updates, support, filing, or remittance; those responsibilities stay with the operator.

Platforms

OpenSalesTax is offered as an API and self-hosted software. Source installation and Docker are supported, with PostgreSQL required by default and MariaDB available as an optional database path. It is not presented as a hosted web application, so teams seeking a turnkey service should consider a hosted alternative.

Who it's for

Choose OpenSalesTax when you need a controllable sales-tax calculation component, have engineering capacity for PostgreSQL or MariaDB, and value Apache 2.0 licensing and zero software cost. It can also suit organizations willing to review public source data and verify results themselves.

Look elsewhere when you need complete local-tax stacking in the documented Colorado or Louisiana cases, a managed data pipeline, filing and remittance, or a vendor-backed compliance workflow. The project is pre-1.0, and its public users registry currently has no listed self-hosters or integrators, so buyers seeking an established implementation community should weigh that adoption status.

Pros and cons

• Pros: Free Apache 2.0 licensing removes per-call or subscription cost; self-hosting keeps deployment and data under your control; state-to-district breakdowns and several product categories support detailed integrations; API-key rate limits and usage tracking provide operational controls.
• Cons: PostgreSQL operations and documented data-refresh steps require in-house ownership; Docker restores need the missing psql package added or a source install; Colorado home-rule and Louisiana parish stacking is incomplete; open-access defaults and pre-1.0 status demand deliberate production hardening and validation.

Alternatives

Zamp is a better choice for teams wanting a paid API with a 30-day sandbox and a U.S. plan aimed at audit-ready compliance while scaling.

Vatstack fits developers who want an API and web option, with a free-for-life Developer plan and a Launch tier starting at $0 per month.

Kintsugi is aimed at teams needing global physical and economic nexus monitoring, exposure auditing, and risk assessment through its free plan.

ShipVAT suits users seeking API and web access with a $0-forever plan that includes 100 API calls per month and supported-jurisdiction calculations.

VAT Engine offers free alpha access through an API and web interface, with availability, limits, support, pricing, and features subject to change.

CCH SureTax is the alternative for organizations choosing among technology-only, filing-and-remittance, or fully outsourced service models.

Vertex for e-Commerce provides a paid API and web platform.

Cbox Tax is another free, self-hosted option.

Browse more options in Tax Engine Software.

Verdict

OpenSalesTax is a strong match for technically capable teams that want a no-cost, auditable sales-tax API they can host and adapt.