attest_flutter

Accessibility testing for Flutter — in your widget tests, gated in CI.

Web accessibility tools like axe-core, Lighthouse and WAVE can't test a Flutter app — Flutter paints to a canvas with no DOM, so to those tools your whole app is one anonymous <canvas>. attest_flutter audits accessibility from inside an ordinary WidgetTester: it walks the live semantics tree, measures real colour contrast from rendered pixels, catches layout overflow at 200% text size, and maps every finding to a WCAG success criterion and EN 301 549 clause, pointed at the file:line that produced it. It gates CI on new issues and can print the transcript a screen reader (TalkBack / VoiceOver) would announce.

Honest framing. Automated checks catch roughly a third of accessibility issues — the machine-checkable ones. This does not make your app WCAG- or EAA-compliant, and it complements real screen-reader testing rather than replacing it. It gives you automated coverage of the checkable part plus a structured checklist for the rest.

Correctness is measured, not claimed: every rule is scored against a validation corpus of 109 hand-labelled cases on each CI run and currently holds precision 1.0 and recall 1.0 with zero false positives on clean fixtures (details in the attest core README).

Install

flutter pub add dev:attest_flutter

Quick start

Audit any pumped screen from a widget test:

import 'package:flutter_test/flutter_test.dart';
import 'package:attest_flutter/attest_flutter.dart';

void main() {
  testWidgets('CheckoutScreen is accessible', (tester) async {
    await tester.pumpWidget(const MyApp(home: CheckoutScreen()));

    final report = await tester.auditAccessibility();

    expect(report, passesAccessibilityGate());
  });
}

When the gate fails, the message is grouped and source-located — one entry per finding, each citing its WCAG criterion and EN 301 549 clause with a concrete fix and the file:line to change.

What it checks

Twelve rules across three detection methods that source-level linters can't do:

• Names & roles — unlabeled buttons, images with no alt text, form fields with no label, generic "Button" labels, duplicate/ambiguous names.
• Rendered output — real text contrast measured from the rasterized screen, and layout overflow / reflow when the system font is scaled to 200%.
• Reachability & structure — touch target size, interactive elements hidden from assistive technology, illogical focus order, missing heading semantics.

Every finding cites WCAG 2.1 / 2.2 and the matching EN 301 549 clause, so the output maps to the standard an auditor will actually ask about.

Fail CI on new issues

Write each report to JSON, then let the attest_cli ci command diff a baseline by fingerprint and fail only on new findings — like a coverage gate. It emits SARIF for GitHub's Problems panel and HTML for humans. See the CLI README for a ready-made GitHub Actions workflow.

Screen-reader transcript

auditAccessibility() also returns the sequence a screen reader would announce, in traversal order — the fastest way to hear what your screen sounds like without a device:

final report = await tester.auditAccessibility();
print(report.transcript); // [Your orders, heading, Pay, button, Email, edit box, …]

FAQ

How do I test accessibility in a Flutter app?

Pump the screen in a widget test and call tester.auditAccessibility(), then assert passesAccessibilityGate(). It runs on the flutter_tester — no device, no real screen reader needed for the automated pass.

Why can't I use axe-core, Lighthouse or Accessibility Scanner for this?

Those read the DOM (web) or the Android view hierarchy. Flutter renders its own widgets to a canvas, so they see one opaque surface. attest reads Flutter's semantics tree directly — the same data TalkBack and VoiceOver consume.

Does this make my app WCAG or EAA compliant?

No. No automated tool can. It covers the machine-checkable criteria and hands you a checklist for the rest (meaningful alt text, media captions, real assistive-technology testing).

How do I silence a false positive?

Mute any rule in one line via RuleConfig(disabledRules: {'attest/heading-structure'}). Heuristic rules ship as warnings for exactly this reason.

Related packages

• attest — the pure-Dart rule engine and data model (no Flutter dependency).
• attest_cli — the CI baseline gate and SARIF / HTML / JSON reporter.

Supported versions

Requires Flutter ≥ 3.32 (Dart ≥ 3.8): the snapshot builder maps the tri-state SemanticsData.flagsCollection API introduced there. The support policy: the current and the previous three stable Flutter releases, with each new stable Flutter tracked within one release cycle — semantics-API drift is a standing maintenance commitment, not an afterthought.

API stability

The developer-facing surface — tester.auditAccessibility(), the gate matchers and everything re-exported from the core — is frozen for 1.0: no breaking change within a major. The plumbing classes (SemanticsSnapshotBuilder, RasterCollector, TextScaleCollector) are annotated @experimental: ordinary tests never need them directly, and their signatures may still evolve (notably for integration_test support).

Feedback — especially false positives from real apps — is very welcome on the issue tracker.

License

BSD-3-Clause.