Paste your original CSS in the left panel and the updated version in the right panel, then click Find Differences. Added lines appear in green, removed in red. Upload .css, .scss, .sass, or .less files directly. All processing runs in your browser - nothing is sent to a server.
- All code is processed entirely in your browser - nothing is ever sent to a server.
- Supports .css, .scss, .sass, and .less - all compared as plain text, line by line.
- Formatter or linter runs (property order, whitespace, brace placement) show as many changed lines without touching any actual values - run the same formatter on both files first to isolate real changes.
- This tool compares source text, not computed styles - paste DevTools computed output directly if you need to compare what the browser actually applies.
- For HTML use Compare HTML; for JavaScript use Compare JavaScript.
How to use this CSS diff checker
Paste or upload your original stylesheet on the left and the changed version on the right. Click "Find Differences." The diff shows every added and removed line with line numbers. Toggle Unified or Side-by-Side view. Uploads filter to .css, .scss, .sass, and .less files.
CSS code comparison explained simply
CSS is a list of rules: each rule says "this selector gets these properties." When you diff two CSS files, you're looking for rules that were added or removed, and property values that changed - like a color that went from #007bff to #0056b3, or a margin that changed from 16px to 24px.
The tricky part is that CSS formatters can reorganize dozens of lines at once without changing any actual values. A tool like Prettier might alphabetize all 15 properties in a block - making 14 lines look different even though only one property value actually changed. Those are formatting diffs, not logic diffs.
Think of two product specification sheets for the same TV. One lists "Screen: 55 in, Resolution: 4K, Price: $800" and the other lists "Price: $900, Resolution: 4K, Screen: 55 in." A line-by-line diff would show every field as changed, when really only Price changed. Sorting both lists alphabetically first collapses the diff to one line. Running the same CSS formatter on both files does the same thing.
What to watch for when you compare CSS files
Formatter-driven changes in CSS files
A CSS formatter or linter (Prettier, Stylelint) can change many lines at once - property order, whitespace, brace placement, or semicolons. Run both files through the same formatter before diffing to isolate only the real value changes.
Vendor prefix additions and Autoprefixer output
Adding or removing -webkit-, -moz-, or -ms- prefixes shows each prefix line as added or removed. A single property change run through Autoprefixer can expand to three or four diff lines - one per prefix variant.
SCSS nesting and renamed variables
SCSS nesting means a single selector change can affect many indented child rules. A renamed SCSS variable appears as one removed line and one added line at the declaration, plus a changed line for every use of that variable in the file.
I've seen SCSS variable renames cause panic during code review - a diff showing 40 changed lines when the only actual change is a single variable renamed from $blue to $brand-primary.
Every line that used $blue shows as changed. Looking for the pattern of many changed lines where every line is otherwise identical except for one word is usually the sign of a rename, not a real logic change.
When to use a CSS diff checker
Design system token changes
Compare two versions of a design token stylesheet to see exactly which color, spacing, or typography values changed between design releases.
When tracking design token changes across quarterly releases, I find it useful to isolate SCSS variable declarations into their own file before diffing. A change to $primary-500 buried inside a 600-line token file is easy to miss in a full-file diff. A variables-only file makes the diff all signal and no noise.
Cross-browser stylesheet debugging
Compare the CSS applied in two different browsers by copying the computed styles from DevTools and diffing them to find which properties differ. Note that DevTools computed styles include inherited and browser-default values - expect a much larger diff than the source file would produce.
Theme overrides
When updating a third-party component library, compare the old and new override stylesheets to ensure all custom overrides still apply correctly after the update.
Verifying PostCSS and Autoprefixer output
After running PostCSS or Autoprefixer, compare the input source against the generated output to confirm which transformations were applied and that no rules were dropped or reordered unexpectedly.
Reviewing AI-generated CSS rewrites
When an AI assistant refactors a stylesheet - converting a layout to CSS Grid, migrating from floats to flexbox, or removing redundant rules - paste the original and the new version to verify only the intended rules changed.
Common mistakes when comparing CSS files
Comparing before and after a formatter run
If one file was auto-formatted with Prettier or Stylelint and the other was not, the diff shows every formatting difference: property order, quote style, semicolons, whitespace. Run the same formatter on both files before diffing to see only value changes.
Comparing compiled CSS against SCSS source
Compiled CSS from SCSS looks completely different from the source - nesting is flattened, variables are replaced with their values, and mixins are expanded inline. If you want to compare SCSS logic, compare the .scss source files, not the compiled output.
Comparing minified CSS against readable source
Minified CSS collapses to one or a few very long lines. Diffing minified against unminified shows the entire file as changed and gives no useful information. Always compare files at the same format level.
Pasting computed DevTools styles that include browser defaults
Browser DevTools computed styles include hundreds of inherited and browser-default properties. Comparing computed output from two pages will show massive diffs driven by defaults, not your stylesheet. Compare source files whenever possible; use computed styles only when you specifically need to compare what the browser resolves.
FAQs about comparing CSS code online
What does CSS stand for?
CSS stands for Cascading Style Sheets. The "cascading" refers to how styles are applied in order of specificity and source position - a rule defined later in the file (or in a more specific selector) overrides an earlier one. CSS was first proposed by Hakon Wium Lie in 1994 and standardized by the W3C in 1996.
What does SCSS stand for?
SCSS stands for Sassy CSS (or Sassy Cascading Style Sheets). It is a syntax of Sass (Syntactically Awesome Style Sheets) that extends plain CSS with variables, nesting, mixins, and functions. SCSS uses the same brace-and-semicolon syntax as CSS, so any valid CSS file is also valid SCSS.
Sass itself was created by Hampton Catlin in 2006; the SCSS syntax was introduced in Sass 3 (2010) to make adoption easier for developers already familiar with CSS.
Can I compare SCSS or Sass files?
Yes. SCSS, Sass, and Less files are plain text. The file upload accepts .css, .scss, .sass, and .less.
Does this compare computed CSS?
No. The tool compares the raw CSS source text. Paste computed styles from browser DevTools if you want to compare what the browser actually applies.
Is my CSS private?
Yes. All processing runs in your browser. No code is sent to any server.
Can I compare compiled CSS against SCSS source?
You can paste any two text files, but comparing compiled CSS against its SCSS source will show the entire file as changed - nesting is flattened, variables are resolved to their values, and mixins are expanded. For a meaningful diff, compare .scss against .scss or compiled CSS against compiled CSS.
Does this work with CSS custom properties (variables)?
Yes. CSS custom properties like --primary-color: #007bff are plain text lines. A changed custom property value shows as a single removed and added line at the declaration. Any lines that use var(--primary-color) are unchanged in the source - the visual effect of the change only appears at runtime in the browser.
Can I compare CSS from two different web pages?
Yes - open DevTools in both browsers, go to Elements → Computed, select an element, and copy the computed styles. Paste each into a panel. Keep in mind that computed styles include browser defaults and inherited values, so expect a much larger diff than the stylesheet source would produce.