CSS Validator: Find Unbalanced Braces & Broken Rules
Paste a stylesheet and get a line-numbered report of the structural mistakes that silently break CSS (mismatched braces, unclosed blocks, empty rules and unterminated comments) checked locally, with nothing uploaded.
What is the css validator?
The CSS Validator is a structural linter that walks pasted stylesheets to catch unbalanced braces, unclosed and empty rules, and unterminated comments or strings, pinpointing each to a line. It's a balance checker rather than a full W3C validator. Free and browser-based, so unreleased design tokens and client themes stay private.
The GigAI CSS Validator is a fast, structural linter for stylesheets: paste your CSS and it walks the source character by character to surface the mistakes that a browser silently swallows but that quietly break the rest of your styles. It counts braces to find unbalanced `{` and `}`, reports the exact block left unclosed, flags empty rule bodies that do nothing, and catches an unterminated `/* … */` comment or an open string literal that would otherwise eat everything after it. Each finding is tied to a line number, and a column where the analysis can pin one, so you jump straight to the fix instead of bisecting a minified blob by hand. It is deliberately honest about what it is: a structural and balance checker, not a full W3C validator that knows every property, unit and vendor prefix. That focus is the point: the overwhelming majority of “my CSS just stopped working” bugs are a single missing brace or a comment that never closed, and this catches those in the moment. Because it runs entirely in your browser with no network requests, you can safely lint unreleased design-system tokens, a client's proprietary theme or a half-built component sheet: nothing you paste is uploaded, logged or seen by anyone, and closing the tab erases it completely.
- Difficulty:
- Easy
- Typical time:
- ~30s
- Processing:
- 100% browser processing
Last updated
How to use the css validator
- 1
Paste or drop your CSS
Copy a stylesheet, a single rule block, or a whole compiled bundle into the box, or drag a.css file onto it. You can also load the built-in broken sample to try it.
- 2
Read the line-numbered findings
The report groups results by kind (structure, blocks, comments and strings) with each error or warning tied to the line (and column where available) it occurs on.
- 3
Fix from the top down
Start with the first structural error: an early unclosed brace or comment cascades into everything below it, so fixing it often clears several downstream findings at once.
- 4
Re-check until it's clean
Paste the corrected CSS back in and confirm the report shows no errors. Copy or download the findings if you want to share them with a teammate.
What CSS Validator includes
Brace-balance checking
Walks the whole stylesheet counting { and }, so a single missing or extra brace (the number-one cause of a broken cascade) is caught and reported instead of silently swallowed.
Unclosed & empty block detection
Tells you exactly how many rule blocks were left open at the end of the file, and flags empty {} rules that add bytes and confusion without doing anything.
Comment & string awareness
Understands /* comments */ and quoted strings, so braces inside them don't cause false alarms, and an unterminated comment or open string literal is caught precisely.
Line-numbered findings
Every issue carries the line it occurs on (and a column where we can pin one), so you jump straight to the fault in even a large or minified stylesheet.
Private, in-browser linting
The parser is native JavaScript running on your device. No upload, no account, no logging. Lint proprietary themes and unreleased tokens with confidence.
Instant, sample-ready
Paste, drop a .css file, or load the built-in broken sample to see the linter in action. Results update as you type, with copy and download for the report.
Why use our css validator
Find the one broken brace fast
When a stylesheet mysteriously stops applying below a certain point, it's almost always a missing } far above. This pinpoints it in seconds instead of a manual bisect.
Clean up before you ship
Empty rules and stray closing braces slip in during refactors. Catching them keeps your CSS lean and prevents a later editor from being confused by dead blocks.
Honest about its scope
It won't pretend to be a full property validator. Knowing it checks structure (not every value) means you trust its passes and never chase a phantom “error”.
Safe for confidential styles
Everything runs locally, so client theme files, design-system internals and unreleased component sheets never leave your machine.
Built for the way you work
From quick one-off fixes to daily workflows, see how people put this tool to use.
- Frontend developer
Track down a broken cascade
Paste a stylesheet whose lower rules stopped applying and let the brace counter point to the unclosed block above that's swallowing everything after it.
- Design-system maintainer
Sanity-check token and theme files
Lint generated or hand-edited token sheets before publishing to catch an accidental empty rule or a stray brace introduced during a refactor.
- Student / learner
Understand a CSS syntax error
See in plain language why a stylesheet is malformed (an unterminated comment, a missing brace) with the exact line, instead of a browser silently ignoring the rest.
- Agency / freelancer
Vet a client's stylesheet
Quickly structurally validate a stylesheet you inherited, entirely offline, before you build on top of it or hand it back with a report.
Supported formats
Accepts CSS, Text and .css file, and produces Validation report, all processed locally in your browser.
- CSS
- Text
- .css file
- Validation report
Frequently asked questions
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Common problems, solved
Hit a snag? Here are quick fixes for the issues people run into most.
It says my CSS is valid but the browser ignores a rule.
This linter checks structure (balanced braces, closed blocks and comments) not whether every property name, value or unit is real. A rule with a typo'd property (e.g. color instead of color) is structurally fine but the browser drops it. Double-check the property spelling and value syntax against MDN.
I get an “unclosed block” error but my braces look balanced.
A brace hidden inside an unterminated /* comment */ or an open string can throw the count off. Fix the earliest comment/string error the report lists first, it's often the real cause, and the brace count usually resolves once that's closed.
It flags a brace inside content: "{" as unbalanced.
The linter tracks strings, so a brace inside matched quotes is ignored. If it still miscounts, check that the string is actually closed. A missing end quote makes everything after it look like string content and desyncs the parser.
Does it validate SCSS, Less or nested CSS?
It treats input as plain CSS. Modern native nesting and simple SCSS usually pass the brace/structure checks, but preprocessor-only syntax (variables, mixins, @-rules with unusual bodies) isn't understood: compile to CSS first for a meaningful check.
Get the most out of it
Fix the topmost error first: an early unclosed brace or comment cascades into a pile of misleading downstream findings.
If the whole file reads as one giant block, look for a comment you opened with /* but never closed with */.
Run it on your compiled/bundled CSS, not just source, to catch structural issues a build step may have introduced.
Empty {} rules are harmless but noisy, delete them so future editors aren't left wondering what belonged there.
For preprocessor code (SCSS/Less), compile to plain CSS first. This checks the CSS structure, not the preprocessor syntax.
What's new
Recent updates and improvements to the css validator.
Initial release, brace-balance checking, unclosed/empty block detection, comment and string awareness, and line-numbered findings, all in the browser.
Added a grouped report (structure, blocks, comments & strings), an at-a-glance stats strip, a built-in broken sample and .css drag-and-drop.
Refined string/comment tracking to eliminate false brace-count errors and clarified the honest-scope note distinguishing structural linting from full W3C validation.
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Explore categories
By file type
Common tasks
Your privacy is built in
Your CSS is validated entirely in your browser with a native JavaScript parser. Nothing is uploaded, stored or logged. Proprietary themes, unreleased design tokens and client stylesheets stay on your device, and closing the tab erases every trace.
- Runs in your browser
- No uploads
- Nothing stored
Ready to try the css validator?
Free, private and instant. CSS Validator runs right in your browser.