How Ziptax sources, verifies, and updates tax data
Ziptax publishes sales tax rate data and state taxability guides for engineers and product teams. A wrong rate breaks a checkout. A wrong taxability position creates an exposure your finance team finds months later. This page covers where our data comes from, who checks it, how often it changes, and how to tell us when we get it wrong.
Who writes and reviews these guides
Guides are written by the Ziptax content team. Every guide carries a visible last-reviewed date and a named reviewer, and nothing publishes without both.
Where rate data comes from
Rates shown in a guide are the values the Ziptax API returns, checked against the live API on the date shown on that page.
The API's rate data is compiled from state and local taxing authority websites. Current coverage:
- 12,000+ U.S. taxing jurisdictions, counting state, county, city, and special district as separate jurisdictions.
- 80,000+ geographic boundaries, which is what allows a lookup to resolve to a street address rather than a ZIP code. ZIP codes are postal routes, not tax jurisdictions, and they cross jurisdiction lines.
- Every U.S. sales tax jurisdiction, plus Canadian rates.
How we determine taxability
Rates and taxability are different problems and we source them differently.
A rate is a number tied to a location. Taxability is a legal position about a product, and it comes from statute, regulation, and department guidance, not from our engine. Where a guide states that a category of software is taxable or exempt in a state, that position is sourced to a named primary document: the statute, the regulation, or the revenue department's own published guidance. Those documents are listed under Sources on every guide, with links, so you can check the position without taking our word for it.
TaxCloud, which Ziptax is part of, is a Certified Service Provider in the Streamlined Sales Tax Program. Where a member state publishes and certifies a taxability matrix, that is our starting point, because it is the state's own classification rather than a third party's reading of it.
Where a state's position is unsettled, or where pending legislation changes it, the guide says so rather than picking a side.
How code examples are handled
Every request and response example in our guides is [run against the live API before publication / illustrative, and labelled as such]. Examples state the endpoint version they were written against. When an endpoint version changes, examples are updated on the next review cycle.
Corrections
If something here is wrong, tell us and we will fix it. Email support@zip.tax with the page and the source that contradicts us. We correct the page, update the last-reviewed date, and record what changed.
Our commercial interest
We sell a sales tax rates API, so we have a commercial interest in you concluding that rate lookups are hard. We are not going to pretend otherwise.
What we do about it: every factual claim in a guide links to a primary source you can check independently. And where the honest answer is that you do not need an API, the guide says that. If you sell into one state at one rate, a hard-coded constant is the correct engineering decision, and we would rather tell you that than sell you a subscription.
What these guides are not
These guides are technical documentation, not tax or legal advice. They describe how the rules work well enough to build against. They do not account for your specific facts, and registration, filing, or prior-exposure decisions should go through a tax professional. Ziptax returns rates and taxability data. It does not file returns and does not determine your filing obligations.