When should I use Inline vs Side-by-Side view?

Side by Side is best for long files and code review — both versions visible at the same scroll position. Inline is best for narrow screens, short snippets, or reading changes as a sequence (deleted line followed by added line). Pick based on screen real estate and use case.

How does this differ from git diff?

This tool computes the same kind of line diff but operates on arbitrary text rather than git history. Use this for ad-hoc comparisons (configs across environments, API responses, AI-generated code) where the content isn't in a git repo.

Why are there so many changes when files look similar?

Whitespace, line endings (CRLF vs LF), or trailing spaces can produce noisy diffs. Enable Ignore whitespace to skip changes that are only spaces, tabs, or trailing whitespace and see only the meaningful differences.

Code Diff Checker — Free Online Code Compare Tool

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What Is a Code Diff Checker?

A code diff checker (or "compare tool") highlights the differences between two versions of a text file or code snippet — typically line by line, with added lines shown in green and removed lines in red. Developers use diff tools constantly: reviewing pull requests, spotting regressions, comparing config files between environments, or debugging the difference between "what I expected" and "what I got" from a code generator. Unlike a plain text diff, a code diff understands syntax and applies language-aware highlighting on top of the change markers.

Code Diff Checker Online — What This Tool Does

This free code diff tool compares two snippets side-by-side or inline using the Monaco diff engine — the same diff viewer used inside VS Code. Pick a language for syntax-highlighted output, toggle whitespace handling, swap left/right, and the diff updates live as you type. Supports JavaScript, TypeScript, Python, CSS, HTML, JSON, SQL, and 15+ more languages. No account, runs entirely in your browser.

How to Compare Code — Step by Step

Paste your original code into the left pane and the modified version into the right pane.
Changes highlight in real time — green for insertions, red for deletions, unchanged lines remain plain.
Pick a language from the dropdown to enable syntax highlighting (JavaScript, Python, SQL, etc.).
Switch view mode — Inline shows one column with markers; Side by Side shows two columns.
Toggle Ignore whitespace to skip changes that are only spaces, tabs, or trailing whitespace.
Toggle Word wrap to wrap long lines instead of horizontal scrolling.
Click ⇅ Swap to flip left and right — useful when you realised you had them backwards.
Click Clear to reset both panes.

Inline vs Side-by-Side — Which View?

Side by Side — best for long files or refactors. Compact change markers in the gutter, both versions visible at the same scroll position. Use this for code review.
Inline — best for narrow screens, short snippets, or when you want to read the diff as a sequence (deleted line followed by added line). Use this for change log entries or quick "what changed here?" checks.

Supported Languages

JavaScript, TypeScript, JSX, TSX, Python, HTML, CSS, SCSS, Less, JSON, SQL, Markdown, YAML, XML, Shell, Go, Rust, Java, C#, C, C++, PHP, Swift, Kotlin, and plain text. Picking the right language enables syntax-aware highlighting on top of the line-by-line diff — keywords, strings, and comments stay correctly coloured inside both added and removed regions.

Common Use Cases

Pull request preview — paste before/after to sanity-check a change before opening the PR.
Config drift — compare .env, config.yaml, or Kubernetes manifests between environments to find what diverged.
API response comparison — paste two JSON responses to spot which field changed.
Formatter / linter audit — see exactly what Prettier or ESLint will rewrite before committing.
AI code review — compare AI-suggested code against your original to spot unwanted edits.
Translation / copy comparison — diff two text files to find changed sentences.

Tips & Tricks

Ignore whitespace for noisy diffs — a re-formatted file becomes 100% changes without this toggle. Enable it to see only the meaningful differences.
Pick the right language — comparing JSON as "plain text" still works but you lose the structural sense of where the change actually lives.
Swap for big-to-small refactors — if you accidentally pasted the bigger file on the left, click Swap to flip the perspective in one click.
Long lines? Use word wrap — instead of horizontal scrolling. Faster to skim long config or SQL lines.
Pair with formatter — run both inputs through our JSON Formatter or JavaScript Formatter first to neutralise whitespace differences before diffing.

Code Diff vs Text Diff vs Git Diff

Code diff (this tool) adds language-aware syntax highlighting to the diff view, making code easier to scan. Text diff compares two strings line-by-line without understanding syntax — see our Text Diff Checker for plain prose. Git diff is the command-line tool that compares the working tree to a commit — same underlying algorithm but tied to a repository's history.

Related Tools

Text Diff Checker — Compare plain text without syntax highlighting (essays, prose, emails).
JSON Diff Checker — Compare two JSON objects semantically, ignoring key order.
JSON Formatter — Pretty-print both sides before diffing to normalise whitespace.
JavaScript Formatter — Normalise JS formatting before comparing changes.
Duplicate Line Remover — Clean repeated lines from logs before comparing.

Is My Code Sent to a Server?

No. The diff is computed entirely in your browser using Monaco's built-in diff algorithm. Your code — including private snippets, proprietary configs, and credentials — never leaves your device. There is no upload, no log, and no analytics on the content you compare. This matters: diff tools are a common place where developers accidentally paste production secrets.