Conformance

Saturon's parser is built from the CSS color grammar rather than a set of per-format patterns. The most direct way to check that claim is to run it against the same tests browsers use.

Saturon's test suite clones the web-platform-tests (WPT) repository, the shared cross-browser test suite for the web platform, and checks the color strings in its CSS color parsing tests with Color.isValid(). Each string is expected to be either valid or invalid, and Saturon has to agree.

Current results

• WPT commit: a15a314
• Saturon version: v0.4.4
• Last run: October 17, 2026

How the tests run

The test clones WPT (shallow and sparse, only css/css-color) and reads every .html file in css/css-color/parsing. Each file's inline scripts are evaluated in a sandbox that records calls to WPT's test_valid_value, test_invalid_value, and test_computed_value helpers. Only cases for the color property are kept.

Two kinds of cases are left out, 61 in total, because they can't be judged from the string alone:

• Strings containing var() (1 case)
• Strings containing currentcolor (60 cases)

The 2660 cases that remain break down like this:

What is tested

Each case checks one direction of the grammar:

• Valid strings must be accepted. For example rgb(none none none / .5) and rgb(calc(infinity), 0, 0).
• Invalid strings must be rejected. For example rgb(none, none, none) (legacy comma syntax can't use none) and rgb(10%, 20, 30%) (legacy syntax can't mix percentages and numbers).

Rejecting bad input matters as much as accepting good input, since a lenient parser can pass every valid case and still accept strings a browser would throw away.

The tests cover, among others:

• Named colors, system colors, and hex colors
• rgb(), hsl(), hwb(), lab(), lch(), oklab(), and oklch()
• color() across its predefined spaces
• color-mix()
• Relative color syntax, including nested origin colors and channel keywords
• The none keyword, and calc() with infinity and NaN

What isn't tested

This suite checks validity only: whether a string is accepted or rejected. It does not check the computed values or serialized output of a parsed color. That includes the 1136 computed-value cases, which WPT uses to check what a browser resolves a color to, but which here only have to be accepted as valid. Passing the suite means Saturon agrees with browsers about what is valid CSS color syntax, not that every conversion matches a browser to the last digit.

It also leaves out:

• Cases for properties other than color (background-color and opacity)
• The var() and currentcolor cases listed above
• Everything outside css/css-color/parsing

Run it yourself

The test lives at packages/saturon/src/tests/wpt.test.ts. It needs git and network access, since it clones WPT every time it runs.

git clone https://github.com/ganemedelabs/saturon.git
cd saturon
pnpm install
pnpm test wpt

The test always clones the latest WPT, so results can change as WPT adds or edits cases. The numbers on this page come from the commit listed above, so a run today may not match them exactly.

Found a disagreement?

If Saturon accepts a string that a browser rejects, or rejects one a browser accepts, please open an issue with the exact string and the browser version you tested in.

To see how the parser works, read Dual-Path Parsing.