Color Contrast Checker — WCAG AA & AAA
Check WCAG 2.1 color contrast ratio between foreground and background colors for AA and AAA compliance.
How it works
- 1Enter your values in the fields above
- 2Click "Calculate" — all math runs in your browser
- 3View your results instantly
What to do next
About Color Contrast Checker
Color Contrast Checker is built for developer utility jobs that fit cleanly into a browser tab. Check WCAG 2.1 color contrast ratio between foreground and background colors for AA and AAA compliance. The processing runs in the page itself, which is why the controls update instantly when you change settings and why a freshly loaded page is ready to do real work the moment it becomes interactive.
Color Contrast Checker is implemented on top of standard browser APIs. Inputs are read from the file picker or drop zone, decoded in the browser, processed, and re-encoded into the output format. Files up to 0 MB are well within the comfort zone of any modern browser.
Color Contrast Checker parses your file with standard browser APIs entirely inside the browser, applies the options you selected, and returns a download. The processing has no network step, which means a slow or intermittent connection does not slow down the work — once the page is loaded, only your CPU and RAM are involved.
If you fit any of these descriptions, Color Contrast Checker should slot cleanly into your workflow: data analysts wrangling JSON; frontend developers prepping fixtures; students learning new languages. The tool keeps the controls focused on what matters for each of these use cases.
The right moment to reach for Color Contrast Checker is when you have a focused developer utility job that fits inside a browser tab. Open the page, drop in the file or paste your input, choose the options that matter, and the tool returns the result.
On limits: 0 MB per file is the ceiling. Output formats and quality settings are listed in the controls panel above, and they apply to every run.
Workflow tip: Color Contrast Checker pairs well with Color Picker and HEX to RGB Converter. Other adjacent tools you may find useful are Color Blindness Simulator and Color Palette Generator. Because every tool is a separate page, you can mix and match the steps that match your job. Bookmark the ones you reach for the most.
The transformation in Color Contrast Checker is deterministic — the same input plus the same options produces the same result every run. That predictability matters when the result has to match an upstream specification or be reproducible later.
The download is delivered as a clearly named file the moment processing completes — no email link, no "your result will be ready in 5 minutes" queue, no expiry timer. The file is generated in your browser and saved by your browser's normal download flow.
Some context on why Color Contrast Checker exists in this form: modern File APIs, high-performance JavaScript engines, and well-maintained open-source libraries now make it possible to perform developer utility work entirely in the browser. Color Contrast Checker is built on top of that capability, which is why a single page can host the full pipeline.
If you also use a command-line tool for color contrast checker, Color Contrast Checker is a convenient alternative for the times you are on a different machine or helping someone who is not comfortable in a terminal. The output is a standard file in the format documented above.
Useful patterns when working with Color Contrast Checker: keep the input file open in another tab so you can compare against the result; give the output file a descriptive name when saving so you can find it later (the default name is sensible but generic); and treat each run as independent — the tool has no concept of "history", which means you cannot accidentally pollute one job with leftovers from another.
If Color Contrast Checker appears to hang, the engine is almost certainly still working — large inputs simply take longer to process inside a browser than they would on a server with multi-core scheduling. For inputs near the 0 MB cap, give it up to a minute on a typical laptop before assuming something is stuck.
Color Contrast Checker is intentionally narrow in scope so the common case is fast and the result is predictable. If you ever need a variation it does not cover, browse the rest of the catalog — there is a good chance an adjacent tool already exists, and switching between tools is just a matter of opening another tab.
How it works
- 1Reach the Color Contrast Checker page in your browser to begin.
- 2Add your developer input by dropping it onto the page or browsing for it.
- 3Tweak the controls if the defaults are not quite right for your input. The options are kept short and labelled in plain language.
- 4Trigger processing. standard browser APIs reads your input, applies the transformation, and writes the result back into the page.
- 5Grab the output as soon as the run completes. You can also copy the result instead of downloading if the next tool in your workflow accepts pasted input.
- 6Run additional jobs as needed. The same controls and defaults apply on every run.
Common use cases
- Validate a config blob before pushing to staging using Color Contrast Checker.
- Encode binary content for transport in a JSON body.
- Hash a string for a quick reproducibility check.
- Pretty-print a minified blob during incident triage.
- Compare two API responses to spot a regression.
- Generate boilerplate from a single specification line.
- Generate a quick fixture without leaving the browser.
- Convert between data formats while wiring up an integration.
- Decode a token to confirm its claims during a debugging session.
FAQ
What is WCAG contrast?
WCAG defines minimum contrast ratios for text readability: 4.5:1 for normal text (AA), 7:1 for enhanced (AAA).
What counts as large text?
Large text is 18pt (24px) or 14pt (18.66px) bold. It requires a lower 3:1 ratio for AA.
What ratio should I aim for?
WCAG AA (4.5:1) is the minimum standard. AAA (7:1) provides better readability for all users.
Does it check color blindness?
No — use the color blindness simulator tool separately. This only checks luminance contrast.
What is luminance?
Relative luminance measures perceived brightness. The contrast formula uses it to determine readability.
Is my data safe?
All processing happens in your browser.
Does Color Contrast Checker reduce quality of the result?
Color Contrast Checker is built to preserve quality wherever the underlying developer format allows it. Operations that are mathematically lossless (e.g. structural transformations, lossless re-encoding) round-trip with no perceptible change. Operations that involve a lossy codec inevitably introduce small artefacts at the byte level, but the defaults aim at the sweet spot where output looks or sounds the same to a normal viewer or listener while still being meaningfully smaller or faster than the input.
Will Color Contrast Checker ask me to pay to download the result?
Color Contrast Checker is free to use. The processing runs in your browser, which keeps the per-user cost low enough that the tool can be offered openly. The download is the same file the engine produced — you can use it for as many runs as you need.
Can I use Color Contrast Checker on documents that contain personal data?
Your file is processed inside your browser by standard browser APIs. The engine reads the file's bytes from your tab's memory, computes the result, and writes the result back into the tab. You can confirm what the page does by opening developer tools and watching the Network tab during a run — the requests you see are for the tool's static assets only.
Is the source for Color Contrast Checker available?
Color Contrast Checker is a static page running an open-source engine in your browser, so a typical corporate firewall does not get in the way as long as it allows JavaScript to load from Favtoo. For teams that need to host it themselves on an internal network, the underlying engine (standard browser APIs) is open-source and can be packaged into a private build with the same behaviour. Reach out via the Contact page if that is something you are exploring.
Does Color Contrast Checker require a browser extension or plug-in?
No installation is needed. Color Contrast Checker runs as a normal web page, with no browser extension, no native helper, and no separate desktop client to download. That is partly a privacy choice — extensions can request broad permissions, while a regular page is sandboxed by default — and partly a convenience one: you can use Color Contrast Checker on any computer you have temporary access to without leaving anything installed on it.
Does Color Contrast Checker have an API?
Color Contrast Checker is a browser-only tool by design and does not expose a hosted API. The reason is the same as the privacy story: there is no Favtoo backend doing the work, so there is no service to call. If you need to script the same transformation, the underlying engine (standard browser APIs) is open-source and can be used directly from your own code.
Are there any usage limits on Color Contrast Checker?
Inputs are capped at 0 MB per file, which keeps memory usage stable across phones, tablets and older laptops. You can run Color Contrast Checker as often as you need; every run produces a full-quality result.
Can I process multiple files at once with Color Contrast Checker?
Color Contrast Checker processes one input at a time by design — it keeps memory usage predictable on lower-end devices and makes results easier to verify. To handle a folder, run the tool once per file; the page stays loaded between runs and remembers your last-used settings, so the second run is essentially instant.
Does Color Contrast Checker work on a phone or tablet?
Color Contrast Checker runs in any modern mobile browser — Safari, Chrome, Firefox and the in-app browsers in most messaging apps all support the underlying APIs. Performance depends on the device: a recent phone handles typical inputs nearly as fast as a laptop, while older devices may take a few seconds longer near the 0 MB ceiling. The interface lays out cleanly on small screens, so you do not need to pinch-zoom to see the controls.