Accessibility SLAs: what to write into headless agency contracts

An enforceable accessibility SLA names the standard and conformance level, lists the exact templates and flows covered, requires both automated and manual testing with named methods, sets remediation windows by severity, and states who pays when the launch misses. Without those five elements, the accessibility clause is decoration.

The vague-line problem

Most headless build contracts handle accessibility in a single sentence: the agency will build the site to be accessible, or will follow accessibility best practices. That sentence is worth nothing at launch. When the site ships with a keyboard trap in the checkout and the merchant asks who is responsible, the agency points at the sentence and says the site is accessible enough, and the merchant has no definition to argue against.

The fix is specificity. An accessibility SLA should read like any other SLA in the contract: measurable, testable, and tied to consequences. These are the clauses that make it real.

Name the standard and the scope

Start with the standard: WCAG 2.2 Level AA is the current baseline most US litigation references. Name it explicitly, with the version and level, so there is no argument later about which guidelines apply. Then name the scope: which templates and flows the standard covers. Homepage, product page, collection page, cart, checkout, search, account pages, and the mobile menu are the minimum for a commerce build.

Scope is where vague contracts die. An agency that promises WCAG AA for the whole site will discover at launch that the whole site includes the third-party review widget, the chat bubble, and the marketing team's popups. List what is in scope, list what is explicitly out of scope, and require the agency to flag third-party components that cannot meet the standard before build, not after.

Require testing, not just building

A promise to build accessibly is unverifiable. A promise to test is. The SLA should require automated testing across the scoped templates with a named tool and a zero-critical-issues bar, plus manual testing: full keyboard navigation of every flow, screen reader testing of checkout and navigation, and zoom testing at 200 percent. Name who performs each test and when.

Most importantly, require evidence. Test reports with dates, tool versions, and issue lists should be deliverables, not internal artifacts. The accessibility handoff at launch should include the final test report the way a financial audit includes its statements. If the agency cannot produce the report, the work is not done.

Set remediation windows by severity

Issues will be found. The SLA should classify them: critical issues block launch, serious issues get fixed within a defined window after launch, moderate issues go into the backlog with a date. Critical means a keyboard user cannot complete checkout, a screen reader user cannot navigate, or focus is trapped. These are launch blockers, written into the contract as such.

Tie the windows to the payment schedule. Holding a percentage of the final payment against accessibility acceptance is the single most effective enforcement mechanism, because it converts the SLA from a wish into a milestone. Agencies that know payment depends on the test report staff the testing properly.

Decide who pays for misses

The clause everyone skips: when the site launches below the agreed standard, who pays for remediation? Write it down. The cleanest structure is that the agency remediates issues found within the warranty window at no charge, where the warranty window is at least 90 days and the issues are measured against the agreed acceptance criteria, not against a new scope of work.

Also cover regression. Headless storefronts change constantly: new sections, new apps, new marketing overlays. The contract should state whether the agency's ongoing retainer includes accessibility regression testing and, if not, what it costs to add. The merchants who get burned are the ones who launched accessibly and drifted, with no one contracted to notice.

The one-page version

If your contract negotiation has room for exactly one page on accessibility, make it this: WCAG 2.2 AA on named templates and flows, automated plus manual testing with delivered reports, critical issues block launch, remediation windows by severity, agency fixes misses within 90 days at no charge, and a payment milestone tied to acceptance. One page, five clauses, and the vague line becomes a warranty.