Colour Contrast Checker (WCAG)

About the Colour Contrast Checker (WCAG)

Make sure text is readable for everyone, including people with low vision. Choose a text and background colour to get the WCAG 2 contrast ratio and pass/fail results for AA and AAA at normal and large text sizes, with a live preview.

How to use it

1. Pick or type the text colour.
2. Pick or type the background colour.
3. Read the ratio and pass/fail results.

Tips and good to know

• AA requires 4.5:1 for body text and 3:1 for large text (18pt, or 14pt bold).
• Pure black on white is 21:1, the maximum.
• Light grey placeholder text often fails — check it too.
• Good contrast also helps everyone reading on phones in sunlight.

About developer tools

Developer utilities are some of the most-searched tools online because everyone who touches code needs them, and they are usually needed right now: a minified API response to read, a Base64 string to decode, a token to inspect, a regular expression to debug. The risk with many online versions is that you paste secrets — API keys, tokens, customer data — into a server you know nothing about.

Every developer tool here runs entirely in JavaScript inside your browser tab and uses the standard Web Crypto and encoding APIs where relevant. You can open your browser's network panel and confirm that nothing is transmitted when you use them. Even so, treat production secrets with care: rotate any credential you have shared anywhere you did not intend.

These utilities follow the relevant open standards — RFC 8259 for JSON, RFC 4648 for Base64, RFC 3986 for URL encoding, RFC 7519 for JSON Web Tokens and FIPS 180-4 for the SHA family of hashes — so results match what your servers, libraries and command-line tools produce. Where browsers differ from other runtimes, such as JavaScript's regular expression flavour, the page says so. They are deliberately small and dependency-free so they load quickly on slow connections and keep working as browsers evolve. If a result surprises you, the guide on each page lists the most common causes, which are usually invisible characters, encoding mismatches or copied whitespace.

Popular ways people use developer tools

• Reading a minified API response while debugging an integration or a webhook payload.
• Inspecting a login token to see which claims it carries and exactly when it expires.
• Building and testing a regular expression for form validation before shipping it to users.
• Generating unique IDs for test fixtures, seed data or database migrations.
• Producing a checksum to confirm that a downloaded or copied file has not been altered.

How we build and test our free tools

Every tool in this collection is built and tested by The Curator team. Before a tool is published we check it against known reference results — textbook loan schedules, standard test vectors for hashes, sample files for conversions — and we re-check it whenever browsers change. Each page explains the method so you can verify the answer yourself rather than take it on trust.

The tools run as JavaScript inside your browser tab. When you choose a file, your browser reads it from your disk into memory; the tool processes it and gives you the result as a download. No copy is sent to us or to anyone else, and nothing is kept after you close the tab. That is why these tools are safe for personal documents, and why they keep working on a slow or interrupted connection once the page has loaded.

The collection is free because it is supported by advertising on these guide pages. We never charge for a tool, never add watermarks and never sell what you type. If something doesn't work as described, or you would like a tool we don't have yet, please contact us — new tools are added in regular batches based on what readers ask for.

Frequently asked questions

Which formula is used?

The WCAG 2.x relative luminance and contrast ratio formulas.

Does it check APCA?

No, it follows the current WCAG 2 standard used in most accessibility laws.

Is it private?

Yes.

Is the Colour Contrast Checker (WCAG) really free?

Yes. There is no account, no trial and no watermark. The Curator is supported by advertising on its guide pages, never by charging for tools or selling your data.

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