What is the IRS Assurance Testing System (ATS)?
Short answer
The Assurance Testing System (ATS) is the IRS test environment where software developers and transmitters prove their software before filing live returns.
What it is
Before each filing season the IRS opens ATS, a copy of the Modernized e-File system loaded with that year's forms and business rules. Software developers and transmitters submit the IRS test scenarios and their own cases, fix whatever is rejected, and receive approval to move to production once their submissions pass.
ATS is about the software, not the preparer. A firm using commercial software never touches it; the vendor does.
Why it matters for a tax firm
Software that has not passed ATS cannot transmit live returns, so the test period in the autumn decides which products are ready in January. For a firm choosing new software, "has it passed ATS for this year" is a fair question.
How XyloDocs handles it
XyloDocs' planned tax software must pass ATS for the 2027 season before it can transmit a single live return; XyloDocs tests as its own software developer and transmitter.
Related terms
Read more on XyloDocs
Sources
Questions about Assurance Testing System
Does a tax firm have to pass ATS?
No. ATS is for software developers and transmitters. A firm only needs an EFIN and software that has passed.
When does ATS open?
Usually in the autumn, after the IRS publishes the coming year's schemas and business rules. The exact date changes each year.
Last reviewed: October 16, 2026. This glossary explains terms; it is not legal or tax advice. Check the cited source for the current rule.
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