ATS Testing: How the IRS Tests E-File Software Before the Season

Before your software can transmit live returns for a tax year, the IRS wants to see that it produces correct returns in the right format. That's the Assurance Testing System, or ATS. Here's how it works and how to plan for it.

The reference is IRS Publication 1436, Test Package for Electronic Filers of Individual Income Tax Returns, published for each tax year, along with Publication 4164 for MeF.

What ATS is

ATS is a test environment where software developers send test returns to the IRS. The IRS publishes test scenarios: fictional taxpayers with specific income, dependents, credits and forms. You prepare each scenario in your software, transmit it to the ATS environment, and the IRS checks that the result is right.

It tests two things:

• Format: the XML matches the schema and passes the business rules
• Content: the forms your software supports produce the right amounts for those scenarios

Who has to test

Software developers who want their software to file returns through MeF, and transmitters who send those returns, go through testing as described in Publications 1436 and 3112. Testing is per tax year and per form family. Supporting a new form or a new year means testing again.

How a scenario goes

1. Read the scenario in Publication 1436: the people, the documents, the forms
2. Enter it in your software as a preparer would
3. Generate the return and validate it locally
4. Transmit it to ATS
5. Read the acknowledgment
6. Fix rejects and resubmit until accepted
7. Complete the remaining required scenarios and the communication test

The secret: the ATS scenarios use specific test SSNs and names, and some of them are deliberately built to hit edge cases in the business rules. Treat every reject as a gift, not a failure: each one tells you about a rule your software will hit with a real client in February. Keep a log of every ATS reject and the fix, and turn each one into an automated regression test. The teams that do this find their live reject rate is much lower in the first week, because ATS already showed them where it breaks.

When to start

The IRS releases the test package and opens ATS ahead of each filing season, usually in the fall. Starting as soon as it opens gives you time for the inevitable rejects. Starting in January means testing while your users are waiting.

After ATS

When testing is complete, the software can be used to file live returns for that year. You'll still monitor live acknowledgments closely in the first days of the season, because real returns are more varied than test scenarios.

Plan it like a project

Phase	Work
Before the package	Update schemas and business rules for the new year
Package released	Map each scenario to your forms; build them
ATS open	Transmit, read acks, fix, resend
Complete	Communication test; prepare for live
Season opens	Watch live rejects daily

What a test scenario looks like

A typical individual scenario in Publication 1436 might include a married couple with two children, a W-2 for each spouse, some interest income, a Child Tax Credit claim, and a direct deposit. Another might be a single filer with self-employment income and Schedule SE, or someone claiming education credits. Each scenario lists the documents and expected forms. Your software has to produce a return that matches.

Common reasons ATS submissions are rejected

• Schema version mismatch: submitting with last year's schema
• Missing required forms: a credit claimed without its supporting form
• Name control errors: the first four letters of the last name don't match what the IRS has for the test SSN
• Signature data: PIN or prior-year AGI fields not filled the way the scenario expects
• Arithmetic: a total that doesn't add up across forms

Build ATS into your release process

Teams that treat ATS as a once-a-year event struggle every fall. Teams that do it well:

• Keep every past scenario as an automated test
• Run the full suite on every change to the tax engine
• Track business rules by tax year in data, not code
• Assign one owner for ATS each year, with a backup

That way, ATS becomes confirmation of what your tests already show, not discovery.

Don't forget the communication test

Testing isn't only about returns. Transmitters also prove that they can connect to the IRS systems, send a transmission and retrieve acknowledgments correctly. Plan time for that too, and for the e-Services and credential setup that comes before it.

We have the API

If you'd rather build your product than run ATS every fall, TaxWallet's API covers returns and MeF e-file, so the yearly schema and testing work is handled on our side for the forms we support. DM API on Instagram @taxwallet.ai to talk through what you're building, or see our developers page. Also read what a tax return API should do.

FAQ

What is IRS ATS?

The Assurance Testing System, where software is tested with IRS scenarios before filing live returns.

Do I have to test every year?

Yes, for each tax year and form family your software supports.

Which publication covers ATS for individual returns?

IRS Publication 1436 for that tax year.

Can I skip ATS by using a partner?

If you use a partner's software or API that has completed testing for those forms, the testing obligation sits with them for their software. Confirm the arrangement in writing.