Web Accessibility Tools | Accessibility Resources

This page contains a list of tools that can be used to evaluate the accessibility of web content. These tools are available under an open source licence unless otherwise noted. Inclusion in this list does not imply endorsement.

Note: most accessibility requirements, such as the WCAG success criteria and the requirements in EN 301 549, cannot be evaluated automatically.

Lists of Tools

The Web Accessibility Evaluation Tools List provided by the Web Accesssibility Initiative (WAI) of the World Wide Web Consortium (W3C) is the most comprehensive listing of accessibility evaluation tools available on the Web.
This is a listing that can be filtered by the guidelines or standards that the tools support, the language(s) in which they are available, type of tool (online, desktop, plugin, etc.), the type of assistance provided, etc.
Any tool developer can add their tool. Note that the W3C does not verify the accuracy of the data and that inclusion does not imply endorsement by the W3C.
The section Accessibility Tools in the Web Design Reference maintained at the Univeristy of Minnesota Duluth.
Hilera, José: a11y-evaluation-tools list, Lists of resources for accessibility evaluation and development (no date; accessed on 19.01.2022). (For this site's source code, see a11y-lists on GitHub. José Ramón Hilera González is a professor at the Universidad de Alcalá in Spain.)
Tools zur Überprüfung, Web for All (no date; accessed on 06.05.2022).
Faulkner, Steve: Accessibility testing tools – Updated May 2019. This article lists tools that are used on a daily basis at The Paciello Group (TPG, a member of the Web Accessibility Tools Consortium, which no longer exists). (Originally published on 29.09.2010.)
Tools, 18F Accessibility Guide (no date; accessed on 23.02.2023).
Web Accessibility Tools, Tests and Resources, UTMB Web Resources (no date; accessed on 30.08.2022).
Evaluation tools: undated article by the University of Michigan’s Web Accessibility Working Group that describes the strengths and weaknesses of some of the most popular accessibility evaluation tools.
Peri, Raghavendra Satish: 45 Browser Extensions to Perform Accessibility Testing Effectively, Digital A11Y, 02.06.2020, updated on 03.05.2022.
Chan, Nic: A Complete Guide To Accessibility Tooling, Smashing Magazine, 16.06.2021 (20-minute read).
Hardy, Michael: 3 Accessibility Testing Tools Small Websites Should Be Using, Thumbwind, 21.06.2021.
This article discusses Google Lighthouse, ARC Toolkit and NVDA.
Newton, Keith: The most dangerous accessibility guidance I've read so far, LinkedIn, 15.02.2023.
This post is about an article containing a list of tools that other accessibility experts have identified as dubious (especially overlay tools) and that appears to exists to promote the company's own tool.
~~Colantonio, Joe: Top 21 Accessibility Testing Tools for Automation, Test Guild, 09.02.2018, updated 24.11.2018.~~
This article contains a list to the WCAG 1.0 checkpoints and looks outdated.
~~Stemler, Sam; Statly, Erica: The 25 Best Free Accessibility Tools to Test Your Site, Accessibility Metrics blog, 18.11.2019.~~
This blog post contains outdated links (such as Cynthia Says and achecker.ca, tools that are irrelevant (e.g. for SEO, link checkers) and implicitly presents the company's own tool, which is not well known in the accessibility community, as the best choice.
~~Top 20 Accessibility Testing Tools for Web Applications, Software Testing Help, last updated on 25.10.2022 (accessed on 15.11.2022).~~
Some of the tools listed on this page are rather old and not up to date with current web accessibility standards. Even though this page was last updated in late October 2022, some of the links no longer worked mid November.

Individual Tools

Code Checkers

WebAIM: WAVE Web Accessibility Evaluation Tool. Also available as browser extensions for Firefox and Chrome.
In November 2017, WebAIM added features to check pages across websites; see the blog post New Site-wide WAVE Tools (28.11.2017).
According to the help page, this tool claims to check compliance against WCAG 2.1 and Section 508. The Google Spreadsheet that maps WAVE checks to WCAG 2.1 succes criteria lists 13 criteria on conformance levels A and AA. (Accessed on 06.05.2022.)
The Functional Accessibility Evaluator (FAE) developed Accessible IT Group at the University of Illinois can evaluate the conformance of an entire website against WCAG 2.0 Level A or Level AA and is therefore updated. You need a user account if you want to evaluate an entire website; registration is free of charge. FAE's source code is available on GitHub under the Apache 2.0 licence.
ARC Toolkit is a tool developed by the Paciello Group. It is available as a Chrome extension: see ARC Toolkit in the Google Chrome Store.
Description from the company's website (July 2020): ARC Toolkit is a professional-level accessibility testing tool that gives you the power to quickly and efficiently evaluate screens for accessibility and uncover issues related to the WCAG 2.1 Level A and AA guidelines. This convenient Chrome extension enables you to easily drill down into code level issues and gain in-depth insight into the accessibility of the screen. It’s a must-have tool to identify and address crucial accessibility issues. (Accessed on 06.05.2022.)
axe: the Accessibility Engine: Axe is an open source rules library for accessibility testing. One of its mantras is not generating false positives. See axe-core on GitHub (Mozilla Public License 2.0). See also:
- List of Axe HTML 4.7 rules, Deque University (no date; accessed on 18.06.2023).
- Accessibility Score (Outcome Reports): short explanation of how the Axe accessibility score is calculated.
- How to get the most out of Deque's axe DevTools accessibility browser extension (Deque Systems on YouTube, 31 minutes, 21.01.2022).
  Demo of the axe DevTools browser extension for Chrome. (There is no version for Firefox.) The video show both freely available funtions and options and a few that require a paid subscription.
- Dodson, Rob: Automated testing with aXe -- A11ycasts #15 (Google Chrome Developers on YouTube, 12 minutes, 17.03.2017).
  Note that this tutorial is based on an older version of axe.
- Sutton, Marcy: Axe 3.0 has arrived — here’s what you need to know, Deque blog, 21.03.2018.
pa11y by Nature Publishing Group is described as your automated accessibility testing pal. It is a command line tool that requires Node.js and PhantomJS. This tool is still being maintained. (Last accessed on 06.05.2022.) (Licence: GNU LGPL 3.0.)
See also the website Pa11y.org. Other relevant resources:
- questions tagged pa11y on Stack Overflow.
- Boyer, Ashlee M.: How I Added a pa11y-ci GitHub Action to My Next.js Site (18.06.2022; 12-minute read). This blog post describes a ten-step process. (One of the requirements is NPM.)
- Kelbel, Ryan: Pa11y: Automated Accessibility Tool Review, Sparkbox, 2021.
Polypane is a stand-alone browser for web developers. It is a commercial product that runs on Windows, MacOS and Linux. It does not focus specifically on accessibility but has a number of features that support the creation of accessible web content and auditing the accessibility of web content. The developer of Polypane is Kilian Valkhof from the Netherlands.
- Accessibility overview, Polypane Documentation (no date; accessed on 05.09.2022).
- Find and fix accessibility issues with Polypane (Polypane blog, 19.01.2021, updated on 25.10.2021 (14-minute read).
- A11y Tooling in Polypane (Kilian Valkhof on YouTube, 55 minutes minutes, 2011).
Total Validator: tool that performs several types of checks: HTML validation, validation against WCAG and the US Section 508 requirements, checking for broken links, and spell checking for a small set of languages (English, French, Italian, Spanish and German).
Assistant RGAA, Firefox Browser Add-ons (accessed on 26.07.2021).
See also Bourdon, Noémie; Bonaventure, Simon: L’extension assistant RGAA se met à jour !, Empreinte Digitale, le blog, 22.07.2021.
The AInspector WCAG is a Firefox add-on developed by the Accessible IT Group at the University of Illinois. Like FAE it evaluates the conformance of web content against WCAG 2.0 Level A or Level AA. Like FAE, it uses the ~~OpenAjax Alliance rules and rulesets~~ OpenAjax Alliance rules and rulesets. See also the AInspector Sidebar Documentation and the AInspector Sidebar source code on GitHub.

The following tools are no longer being developed:

European Internet Inclusion Initiative (EIII): EIII Page Checker: tool where you can enter the URL of a web page that you want to evaluate. The tool's “About” page claims it checks conformance against the Web Content Accessibility Guidelines 2.1 (WCAG 2.1) without mentioning a specific conformance level. (Accessed on 06.05.2022.)
See also checker-suite (EIII GitLab repository), which has not been updated since October 2015. This checker suite for large-scale evaluation was developed and used during the EU-funded EIII project. The code is written in Haskell and Python and is available under the BSD three-clause licence. See the blog post Open source release of the automated EIII checker suite (05.10.2015) and the list of Checker HTML Tests.
See also EIII Source. The code in these repositories has not been updated since October 2015.
Squiz Labs: HTML_CodeSniffer / HTML_CodeSniffer (on GitHub): HTML_CodeSniffer is a client-side script that checks HTML source code and detects violations of a defined coding standard. (…) To get you started, HTML_CodeSniffer comes with standards that enforce the three conformance levels of the Web Content Accessibility Guidelines (WCAG) 2.1, and the web-related components of the U.S. "Section 508" legislation. An auditor interface is provided by a bookmarklet to let you try out these accessibility checks on any web page. (The GitHub repository has not been updated since September 2020. Last accessed on 06.05.2020.) Licence: BSD 3-Clause License.
MAUVE: Multiguideline Accessibility and Usability Validation Environment: MAUVE++ (Multiguideline Accessibility and Usability Validation Environment) is a system to evaluate accessibility of websites by checking their HTML and CSS code through guidelines, it provides validation results for different types of stakeholders, and supports validation of W3C WCAG 2.1 guidelines.
See also MAUVE++. Neither site could be reached on 06.05.2022.)
Grunt Accessibility, by Steven Miller is an HTML codesniffer to grade accessibility. It is a command-line tool for checking static HTML pages on your hard drive. You can specify which level of the Web Content Accessibility Guidelines (WCAG) 2.0 the code should be tested against. (Licence: MIT.) The source code has not been updated since early 2018, so it has not been updated since the publication of WCAG 2.0.
WaaT: Web Accessibility Assessment Tool is a Java-based tool developed by the European Project ACCESSIBLE. More information is available on the website of the ACCESSIBLE project. (In “beta” since 2013, with no update since that time. Licence: MIT.)
Google Chrome Accessibility Developer Tools is a library of accessibility-related testing and utility code. The GitHub repository has not been updated since November 2017. (Last accessed on 06.05.2022.) (Licence: Apache 2.0.)
See also Totally Tooling Tips: Accessibility: short YouTube video (8 minutes) by Addy Osmani and Matt Gaunt that introduces a few tools, i.e. the Chrome Accessibility Developer Tools Extension, the Accessibility Developer Tools (a Node module available on GitHub), a11y (a module with a command-line interface that can also be used in continuous integration), Tenon.io (a web-based checker; see the source code on GitHub), tota11y (a bookmarklet; see the source code on GitHub) and ally.js (JavaScript library; see the source code on GitHub.
The video is part of the free online course Web Accessibility by Google on Udacity.
Ember A11y Testing (available under the MIT licence) is a wrapper around Deque Labs' axe-core accessibility testing engine. It integrates into your testing environment with a simple a11yAudit() helper. The GitHub repository has not been updated since November 2017. (Last accessed on 06.05.2022.)
See also Ember A11y on GitHub.
AccessLint: Automated and continuous web accessibility testing. According to its developers, AccessLint is a GitHub App that finds accessibility issues in your pull requests. (20.07.2022.) The AccessLint app in the GitHub Marketplace can be used for free by hobbyists for the personal projects but requires payment if you want to use it for private projects or on an entire organisation on GitHub. (See also the AccessLint app and the other checkers by the organisation AccessLint.
Sa11y: Most accessibility tools are designed for developers and often require knowledge of code to make sense of the results. Sa11y is designed for content authors and focuses on content related issues and successes. (20.07.2022.)
Deque Labs: aXe Selenium (Java) Integration: demonstration of how to use aXe to run web accessibility tests in Java projects.
This repository was deprecated in October 2020. Licence: Mozilla Publice License 2.0.
Koa11y: a desktop app that allows you to automatically detect accessibility (a11y) issues on webpages. It runs on Linux, Windows (XP or more recent) and Mac OS. The tool was created using Pa11y, Vue.js and NW.js. The Koa11y source code is available on GitHub under the terms of the MIT licence. The source code has not been updated since 24.08.2020.
ADA Compliance Testing & Auditing Tools, Accessibility Works blog, 29.06.2022.
AChecker: online tool that can check web pages that you submit by entering a URL, uploading an HTML file or pasting source code. You need a user account if you want to evaluate an entire website. AChecker's source code is available on GitHub under the GNU GPL version 2. The tool was take offline in late 2021 or early 2022. The source code repository has been archived.
Peter Kranz: Raakt - The Ruby Accessibility Analysis Kit. Source code available on Rubyforge.org under the BSD 3-clause licence. (The source code repository could not be reached on 06.05.2022.)
Access-for-all: CAC - The Content Accessibility Checker: a Firefox plugin for checking web content against the subset of WCAG 2.0 success criteria that can be checked automatically. Licence: Creative Commons CC BY 3.0 CH (which is not an appropriate licence for source code!).
The source code repository has not been updated since August 2015. (Last accessed on 06.05.2022.)
Anil Suryanarayana: seleniumAccessibility: Selenium Webdriver driven accessibility testing module to check for webpage accessibility compliance. Licence: MIT License.
The source code repository has not been updated since July 2015. (Last accessed on 06.05.2022.)
tota11y-chrome: a browser extension for Chrome, available under the MIT licence. The GitHub repository has not been updated since September 2015.
access_lint: Check for web accessibility errors from Ruby. Available under the MIT licence. Uses the Audit Rules defined for the Google Chrome accessibility developer tools. (This tool is no longer being maintained. The developer instead recommends AccessLint.
LERA - Website Accessibility Testing & Reporting Tool, Advancedbytez (no date; accessed on 16.11.2022).

Contrast Checkers

Whether foreground and background colous have sufficient contrast is not something that you should try to “eyeball”. For example, red and green are strongly contrastly contrasting colour for people with normal colour vision but not for most people with colour vision deficiencies. There are many free tools that can help you check contrast, find colours with sufficient contrast or simulate certain colour vision deficiencies.

Most contrast analysis tools now support the contrast algorithm defined in the Web Content Accessibility Guidelines (WCAG) 2.0 and will tell you whether the contrast ratio pass at Level AA or at Level AAA. Some tools will also tell you whether the contrast meets the requirements defined in the Techniques For Accessibility Evaluation And Repair Tools (AERT) (August 2000). However, this document never went beyond the W3C working draft stage, and its contrast algorithm is explicitly marked as open to change.

Tools that simulate colour blindness try to approximate what people with colour vision deficiencies see; the output of these tools should not be interpreted as exact renditions of what these people see.

ColorContrast.App since 13 April 2023 the new home of Color contrast checker by Polypane. This is a web-based contrast checker that only accepts hexadecimal RGB values, but also RGBA and HSLA values. The result of the contrast check is available as a sharable link.
Quote: Unlike many contrast checking tools, the Polypane contrast checker takes opacity into account when calculating the colors, giving you the real contrast ratio. (Accessed on 24.02.2023.)
Announcement: ColorContrast.App: a new place for our color contrast checker (Polypane blog, 13.04.2023).
APCA Contrast Calculator: developed by Andrew Somers of Myndex. This contrast checker does not only accept hexadecimal RGB values, but also RGBA and HSLA values. You can generate a sharable link for the test results.
See also the GitHub repository for the APCA Contrast Calculator.
The Colour Contrast Analyser is a free and open source tool for Windows and Mac OS X developed by The Paciello Group (TPGi).
The tool has two main functions:
- Checking whether two colours pass the contrast requirements defined in the Web Content Accessibility Guidelines (WCAG) 2.0. You can identify colours using a “eye dropper” toolor using hexadecimal RGB colour codes.
- Simulate certain colour vision deficiencies. (The visual simulation is only available in the Windows version.)
“Working with the colour contrast analyser by the Paciello group” (February 2009) explains how to use this tool, even though this should be rather straightforward.
The contrast analyser is available in several languages (including English, German, French, Hindi and traditional Chinese). The source code is available on GitHub under the GNU General Public License 2.0.
Contrast Ratio (originally by Lea Verou) is a tool for checking the contrast of web colours. Unlike many other contrast checkers, it does not only accept hexadecimal RGB values, but also RGBA and HSLA values. The result of the contrast check is available as a sharable link.
Lea Verou’s article “Easy color contrast ratios” (October 2012) gave the tool a wider visibility in the web development community. (See also Scott Gilbertson’s article “Create More Accessible Color Schemes With ‘Contrast Ratio’”.)
The source code is available on GitHub under the MIT License and is owned by an SEO company since March 2023. (See Contrast Ratio has a new home — and this is great news!, 18.03.2023.)
Contrast, Nothing Magical (accessed on 05.07.2022).
This is a Mac OS application (and not free of charge).
Accessible Colors: WCAG 2.0 AA and AAA color contrast checker: this contrast checker is somewhat different because it does not only allow you to enter the colours you use but also the font size (in pixels) and font weight. It only accepts hexadecimal RGB values.
Contrast Check by Accessibility Check is a checker that accepts various types of values. It was probably inspired by Lea Verou's web-based tool.
Contrast Checker, WebAIM.
This tool can also be used as an API by adding colour codes to its URL. Like most other contrast checkers, it only accepts hexadecimal RGB values.
Tanaguru Contrast-Finder.
(See also the Tanaguru Contrast-Finder GitHub repository.)
Contrast Ratio Calc by a certain José or jfmdev is a web-based contrast checker that allows you to store various colours for comparison. However, it only accepts hexadecimal RGB values, not RGBA or HSLA values. The result of the contrast check is available as a sharable link.
See also the Contrast Ratio Calc GitHub repository, where the code is available under the terms of Mozilla Public License v2.0.
DigitalA11Y Color Contrast Checker is an extension for Chrome developed by digitala11y.com.
A11y accessibility check for text colour on background image: this is a web-based tool that allows you to upload an image and have text contrast issues tested.
Tester le contraste des couleurs.
Annika Hamann’s Contrast-A is another tool for identifying accessible colour combinations. Like Giacomo Mazzocato’s colour wheel, it supports both WCAG 2.0’s contrast algorithm and the older AERT algorithm.
Warning: this tool is developed in Adobe Flash and is not keyboard accessible. This tool could no longer be reached on 23 January 2023.
Giovanni Scala’s Check My Colours is a web-based tool for checking contrast in existing web pages. You can enter the URL of a web page to check the foreground and background combinations of all DOM elements. The tool uses both WCAG 2.0’s contrast algorithm and the older AERT algorithms. Its output is a table where each row represents a DOM node, its foreground and background colour (as hexadecimal RGB codes), a sample, and the output of three algorithms: WCAG 2.0’s algorithm, AERT’s brightness difference algorithm and AERT’s brightness colour difference algorithm.
The tool is available under the Creative Commons Attribution-ShareAlike 2.5 Italy (CC BY-SA 2.5 IT) Licence. This tool was no longer available on 24.02.2023. A message said, Sorry! Service has been discontinued.

Articles on Checking Contrast

Bracey, Kezz: How to Use the Contrast Checker in Chrome DevTools, Envato Tuts+, 22.10.2018.
Dennis: Color Contrast Tools, Web Axe, 23.01.2016, last updated in June 2021 (accessed on 24.02.2023).
This is just a list of links to contrast checkers.
Whiting, John: Evaluating Color and Contrast – How hard can it be?, WebAIM blog, 02.07.2021.
This blog post discusses all the types of content and elements that need to be checked. It does not take opacity or transparency, nor colour gradients into account.
Sethfors, Hampus: Top seven free color contrast checkers & analyzers, Axess Lab, 03.06.2022.

Accessible Colour Pickers

Joe Dolson's Color Contrast Spectrum Tester is an online tool that helps you find colours that provide sufficient contrast with a colour of your choice. You can choose a colour using a colour picker or a hexadecimal code and then let the tool generate a number of colours. Each of the generated colours will be tested against WCAG 2.0's contrast requirements; those that pass WCAG 2.0 will be displayed with their luminosity ratio.
The tool is also available in several languages, namely English, French, Dutch, Portuguese and traditional Chinese.
Accessible color palette builder: web-based tool by Atul Varma tool for choosing accessible colour combinations. The tool's source code is available on GitHub.
Maark; Carr, Alex: Contrast, Figma Community, 2019 (accessed on 25.02.2023).
Giacomo Mazzocato’s Accessibility Color Wheel is a web-based tool that helps you identify accessible colour pairs that you can use in web content. It implements both WCAG 2.0’s contrast algorithm and the older AERT algorithms (which it identifies as the WCAG 1.0 algorithm, even though WCAG 1.0 did not specify a contrast algorithm). This time was not online on 24.02.2023. A message said, The web site has been archived, access to the control panel to restore it.

Colour Blindness Simulators

Vischeck is a tool that simulates colour vision deficiencies (“colour-blind vision”). The tool was developed at Stanford University; the Info & Links page provides information about the algorithms in the code and points to other interesting web pages about colour blindness.
You can run Vischeck on image files you upload or run Vischeck on a webpage (offline on 11.11.2021).
Daltonize is a tool that corrects images for colorblind viewers.
Color Oracle is a free and open source tool that simulates colour blindness. Color Oracle’s website also provides design tips for maps and information graphics that are accessible for colour-impaired readers.
The tool is written in Java and works on Windows, Mac OS X and Linux. Color Oracle’s source code is available on GitHub under the MIT License.
Sim Daltonism: The color blindness simulator. This simulator, developed by Michel Fortin, is available for iOS and Mac OS. The source code is available under the terms of the Apache 2.0 License in the sim-daltonism GitHub repository.
Coblis — Color Blindness Simulator is a colour blindness simulator where you can upload images and see what they look like through eight different simulations of colour blindness.
See also Coblis1 – Color Blindness Simulator, the first version of the simulator.
Colorblind Web Page Filter, Toptal (accessed on 11.11.2021).
This is a page where you can enter a web page URL and choose type of colour vision deficiency that should be simulator for that page (protanopia, deuteranopia, tritanopia or achromatopsy). This may not work well for pages with a lot of dynamic content.
Myndex™ Color Vision Deficiency Simulator: developed by Andrew Somers of Myndex. This page allows you to upload an image and check what it looks like for several types of colour vision deficiencies.
RGBlind is an open-source real-time color blindness simulation tool for the web. It can be used as a web page where you can enter a URL: Online color blindness simulator for URLs It is also available as a browser extension for Google Chrome, Firefox and Opera. See for example, RGBlind on the Firefox Add-ons site. For the source code, see the RGBlind repository on GitHub, where the source code is available under the terms of the MIT licence.
Chromatic Vision Simulator: an app for iOS and Android. The Chromatic Vision Simulator - Web Edition can either use your camera or you checks an image you have uploaded.
Colorblindly Color Blindness Simulator, We are Colorblind, 16.11.2018.
Colorblindly is a Chrome extension that simulates eight different types of colour blindness.
Esser, Olivier: The daltoniser: webpage about an old simulator based on the paper A Physiologically-based Model for Simulation of Color Vision Deficiency by Gustavo M. Machado, Manuel M. Oliveira and Leandro A. F. Fernandes (2009).
~~Color Vision Deficiency is a GIMP plugin that simulates different colour vision deficiencies.~~
Petrich, Loren: Color-Blindness Simulators. ~~The Color-Blindness Simulator for Webpages is no longer working.~~

Articles about Automated Accessibility Evaluation

Mundra, Daniel: How I do automated accessibility testing for my website, Opensource.com, 22.02.2023.
Subtitle: Follow along with this example of performing accessibility tests in GitLab with Pa11y and Cypress on a Jekyll website.
Accessibility inspector - Firefox Developer Tools, MDN, last updated 20.06.2018 (accessed 02.07.2018).
Cashin, Caitlin: The Engine Driving Web Accessibility Standardization, Caitlin Cash (on Medium), 10.01.2018.
Holbrook, Dan: The Power (and Limits) of Automated Accessibility Testing, Nerdery, 01.06.2017.
Groves, Karl: Choosing an Automated Accessibility Testing Tool: 13 Questions you should ask, 28.06.2013.
Faulkner, Steve: WCAG 2.0 Parsing Criterion is a PITA, Paciello Group blog, 20.11.2015.
Faulkner, Steve: WCAG 2.0 parsing error bookmarklet, Paciello Group blog, 02.02.2012.
(The bookmarklet does not seem to work in recent versions of Firefox.)
Faulkner, Steve: WCAG 2.1 parsing error bookmarklet – updated 25th February 2019 Paciello Group blog, 25.02.2019.
Groves, Karl: Efficiency in Accessibility Testing or, Why Usability Testing Should be Last, Karl Groves, 22.04.2012.
Barrierefreiheitstests – automatisiert, manuell, egal?, marcus-herrmann.com (no date; accessed on 23.02.2023).
Automated Accessibility Testing Tools: How Much Do Scans Catch?, Level Access blog, 01.12.2020.
Klavenes, Lars Magnus: How to test for accessibility with axe-core in Next.js and React, larsmagnus, 21.05.2022.
Durah, Mehmet: What we found when we tested tools on the world’s least-accessible webpage, Accessibility in government, 24.02.2017.
Zehe, Marco: Introducing the Accessibility Inspector in the Firefox Developer Tools, Marco's Accessibility Blog, 11.04.2018. Marco Zehe points out that the inspector is only intended as an inspection tool, not as an evaluation tool.
Adam, Paul: Accessibility Testing Tools for Desktop and Mobile Websites, 24 Accessibility, 19.12.2017.
Bean, Iain: An opinionated guide to accessibility testing, Iain Bean, 14.10.2020.
Burns, Heather: Equal Entry Website Mistakenly Called Out as Inaccessible, Equal Entry, 31.07.2020.
A visitor left a comment on the Equal Entry website claming that the site had accessibility issues. It turned out that they had interpreted certain issues flagged by WAVE as representing real issues, whereas in reality they were either false positives or just alerts rather than errors. The issues reported by WAVE had not been reported by Microsoft Insights for Web, nor had they been obvious during a test with NVDA.
Roselli, Adrian: Comparing Manual and Free Automated WCAG Reviews, Adrian Roselli, 19.01.2023, updated on 23.01.2023.

Developing Browser Extensions

Google Chrome Extensions and Accessibility is a short video by Rachel Shearer (from Google's accessibility team) discusses accessibility best practices for extension developers. In the first part, she describes the ChromeVis extension (for people with low vision). In the second part, she explains how she used the WebKit selection API and what kinds of additional work was needed for features such as keyboard navigation, text size options and colour options. ~~The source code for Chromevis has been archived on code.google.com.~~ See also the chrome.accessibilityFeatures API that was introduced in Google Chrome 37 (but which only works on Chrome OS).

Stylesheets for Finding Issues

Domleo, Jack: Checka11y.css: A CSS stylesheet to quickly highlight a11y concerns. (Licence: MIT licence. Accessed on 27.02.2023.)
Meiert, Jens: QA Style Sheet: CSS file that highlights common HTML problems; not primarly geared towards accessibility evaluation. (Licence: Apache 2.0.)
Groves, Karl: Diagnostic.css: CSS file which allows the user to test for common errors in a page's markup. (Licence: undefined.)
Heydon: REVENGE.CSS: A CSS bookmarklet that puts pink error boxes (with messages in comic sans) everywhere you write bad HTML. (Creative Commons Attribution 3.0 Unported license.)
Diagnostic CSS Files: this CSS is a diagnostic file that aims to highlight HTML elements that have roles that should probably be native HTML equivalents (&ellip;). (Licence: MIT License.)
Stylus, add0n.com (no date; accessed on 07.09.2022).
Stylus is not an accessibility evaluation tool but it is possible to use styles to highlight specific issues.
Writing styles, openstyles/stylus Wiki, last updated on 16.08.2022.
Using CSS and Stylus to bend the web to your will, G. Winney, 10.04.2020.

Various Browser-Based Tools

Stylesheets, bookmarklets and other scripts for visualising specific markup features.

Wilco Fiers: Table Manners: jQuery plugin to visualize accessibility of tables (last updated in 2013; no licence).
Adam, Paul J.: JavaScript Bookmarklets for Accessibility Testing.
These bookmarklets are very useful for people who are not allowed to install browser add-ons for accessibility testing, which is the case in some corporate environments. (See also pauljadam/bookmarklets, the GitHub repository for the accessibility bookmarklets. This repository was last updated in September 2019.) (Accessed on 29.05.2023.)
BOSA Accessibility Check: a bookmarklet for accessibility evaluation made available by the Belgian federal public service BOSA. (GitHub repository: openfed/AccessibilityCheck. Accesssed on 29.05.2023.)
See WCAG 2.1 Standard: Summary - BOSA Accessibility Check for the list of checks supported by the bookmarklet.)
Lighthouse: open-source tool by Google for improving the quality of web pages. It is part of the Chrome DevTools, which are available in Google Chrome and Chromium; they can also be run from the command line or as a Node module. Among other things, it performs accessibility audits. The Lighthouse source code is available on GitHub under the terms of the Apache 2.0 licence.
See also the following blog posts and articles:
- Lighthouse - Totally Tooling Tips (Google Chrome Developers on YouTube, 8 minutes, 08.09.2017).
  This is a general introduction to Lighthouse for webdevelopers without specific attention to accessibility evaluation.
- Dodson, Rob: The new way to test accessibility with Chrome DevTools - A11ycasts #23 (Google Chrome Developers on YouTube, 5 minutes, 18.08.2017).
- Moshe, Dor: The New Chrome DevTool Feature You Want to Know About, Hacker Noon, 06.06.2017 (eight-minute read).
- Loukil, Aymen: Lighthouse custom audits tutorial, Aymen Loukil, 19.11.2018. (This blog post does not mention accessibility audits.)
- Cashin, Caitlin: Google Selects Deque’s axe for Chrome DevTools, Deque blog, 28.09.2017.
- Kennedy, James: Will the Lighthouse accessibility audit tool help make the web more accessible?, Boston Web Designers, 22.11.2017.
- Lighthouse performance scoring, Chrome Developers, 19.09.2019; updated on 09.02.2023.
Accessibility Insights for Web: Overview. This tool was developed by Microsoft.
- Lahoti, Sugandha: Microsoft open sources ‘Accessibility Insights for Web’, a chrome extension to help web developers fix their accessibility issues, Packt Hub, 14.03.2019.
- Accessibility Insights for Web in the Google Chrome Store. (There is no Firefox add-on.)
- accessibility-insights-web (GitHub repository).
ANDI (Accessible Name & Description Inspector), Social Security Administration (accessed on 11.07.2022).
See also ANDI on GitHub. One advantage of ANDI over many other tools is that it is a bookmarklet, so it can even be installed in organisations that don't allow employees to install browser extensions or other software.
tota11y – an accessibility visualization toolkit: a tool developed by Khan Academy.
headingsMap:
- headingsMap (Firefox add-on).
- headingsMap (Chrome extension).
Adam, Paul J.: Headings Bookmarklet for Accessibility Testing, JavaScript Bookmarklets for Accessibility Testing (no date; accessed on 29.05.2023).
This bookmarklet is a convenient alternative to headingsMap for people who are not allowed to install browser add-ons.
Smith, Nathan: Introducing Construct.css, CSS-Tricks, 12.09.2018, updated on 09.02.2019.
TPG Bookmarklets, The Paciello Group (on GitHub), last updated in 2017.

Browser Features and Extensions for End Users

Mozilla Support: Accessibility features in Firefox - Make Firefox and web content work for all users.
Media Access Australia: How to turn on accessibility features in Google Chrome.
Media Access Australia: How to turn on accessibility features in Opera.
@keitori: chrome extensions for disabilities masterpost, keitori.tumblr.com (no date).

Comparing or Benchmarking Evaluation Tools

Government Digital Service (UK): How do automated accessibility checkers compare? / Accessibility Tools Audit Results (February 2017). See also the blog post What we found when we tested tools on the world’s least-accessible webpage (24 February 2017). The tools were tested on these test cases with accessibility failures.
Accessibility Fails by Alistair Duggin and Mehmet Duran is a collection of accessibility failures that can be used to test evaluation tools.

Using Screen Readers for Accessibility Testing

Paladugula, Rakesh: Spectator of Screen Reader? tools for you, Maxability, 02.02.2017.
Whiting, Jon: Three things you should know before using VoiceOver for testing, WebAIM blog, 31.08.2016.
Lockwood, Sue: Getting Started with VoiceOver & Accessibility, Bocoup (blog), 23.02.2017.

Reporting Tools

WCAG-EM Report Tool: interface of an open-source reporting tool developed at the Wold Wide Web Consortium. For docmentation related to the tool, see WCAG-EM Overview: Website Accessibility Conformance Evaluation Methodology, the WCAG-EM Report Tool GitHub repository, the documentation of the EARL + JSON-LD format in the old GitHub repository. (For the documentation of the EARL format, see Evaluation and Report Language (EARL) 1.0 Schema and Developer Guide for Evaluation and Report Language (EARL) 1.0.)
The tool was updated during the WAI Tools project (see Cordis), which ran from November 2107 till January 2021 and had a total budget of 2 244 493,75. The update to the tool was only of the project's goals. See also the WAI Tools page at the W3C.
The first version of the WCAG-EM Report Tool was developed with support from the WAI-ACT project, which ran from September 2011 till August 2014 and had an overall budget of € 1 567 718. See also the WAI-ACT project page at the W3C and the GitHub repository of the first version of the tool.
Be Inclusive: a commercial tool developed by Steve Woodson (Chicago, USA). The user interface is available in English, Spanish, French and Dutch.
CAAT: a commercial tool developed by mindscreen (Munich, Germany). The user interface is available in German and English.