Code Diff Viewer

Compare two code snippets and visualize differences with line numbers and color-coded highlighting.

Original

Modified

About Code Diff Viewer

Code Diff Viewer is a free online tool that compares two code snippets and highlights the differences between them. It uses the LCS (Longest Common Subsequence) algorithm to compute an accurate line-by-line diff with color-coded output.

All processing happens entirely in your browser. No data is sent to any server, ensuring complete privacy for your source code.

How to Use

Enter original code — Paste the original version of your code in the left panel.
Enter modified code — Paste the modified version in the right panel.
Compare — Click the Compare button to see the diff result with additions, deletions, and unchanged lines highlighted.

Frequently Asked Questions

Q: Can I compare files with thousands of lines?

Yes. The diff viewer handles files up to around 10,000 lines comfortably. For very large files, computation may take a few seconds since the LCS algorithm runs entirely in your browser.

Q: What algorithm is used for diffing?

This tool uses the LCS (Longest Common Subsequence) algorithm, the same approach used by Git and other version control systems for computing diffs.

Q: Does it work with any programming language?

Yes. The diff viewer compares text line by line and works with any programming language or plain text content.

Q: What do the colors mean?

Green indicates added lines (present in modified but not in original). Red indicates removed lines (present in original but not in modified). Gray indicates unchanged lines.

Q: Is there a size limit?

Since all processing happens in your browser, very large files (over 10,000 lines) may take a moment to compute. There is no hard limit.

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Introduction

Diff Viewer compares two blocks of text and highlights exactly what changed between them. Added lines show up in green, removed lines in red, and untouched lines stay in a neutral shade so your eye can land straight on the delta. It is the same shape of output that git diff produces on the command line, but rendered in the browser with no setup.

Reaching for a diff is the default move whenever you suspect a change was made: two copies of a config file, yesterday's production build vs. today's, a patch someone emailed you, the result of a refactor that should have been a no-op. Seeing the changes side by side turns a vague question ("did anything move?") into a concrete answer.

The diff computation runs locally in your browser using a Longest Common Subsequence algorithm, the same technique Git uses. Neither the original nor the modified text leaves the tab, which keeps the tool usable for proprietary source, infrastructure configs, and other material that should not be uploaded to third-party services.

How to Use

Paste the baseline version of your text into the left editor.
Paste the modified version into the right editor.
Hit Compare. The viewer computes the LCS, then paints additions, deletions, and unchanged lines with color-coded markers.
Scan the gutter for line numbers — they track both sides, so you can cross-reference with your source control or editor.
Apply the fixes you agree with, discard the ones you don't, and copy the updated text back into your project.

Examples

Two realistic situations that people diff all the time: a small code change during a refactor, and a configuration tweak during a deploy.

Example 1: Code change during a refactor

A function signature changes to accept an options object instead of positional arguments. The diff makes the two modifications obvious without having to re-read the surrounding lines.

Input

function fetchUsers(limit, offset) {
  const url = `/api/users?limit=${limit}&offset=${offset}`;
  return fetch(url).then((r) => r.json());
}

Output

  function fetchUsers(limit, offset) {
-   const url = `/api/users?limit=${limit}&offset=${offset}`;
+ function fetchUsers({ limit = 20, offset = 0 } = {}) {
+   const url = `/api/users?limit=${limit}&offset=${offset}`;
    return fetch(url).then((r) => r.json());
  }

Example 2: Config change during a deploy

A YAML configuration file has a port change and a new environment variable. The diff flags both lines while confirming the rest of the file is identical.

Input

service:
  name: api
  port: 8080
  env:
    NODE_ENV: production

Output

  service:
    name: api
-   port: 8080
+   port: 8443
    env:
      NODE_ENV: production
+     LOG_LEVEL: info

Target language details

Version assumptions and style choices baked into the generated output. If your runtime is older, you may need to adjust syntax (e.g. drop optional chaining, use `var` instead of `const`).

Language	Version	Output style
JavaScript	ES2017+; works in all evergreen browsers and Node 16+	Functional + async; generated output uses fetch / async-await.
TypeScript	TS 5.x target; interface / type / readonly aware	Interfaces preferred over types for extensibility.

Key Features

Line-by-line comparison using the LCS algorithm — the same approach Git, Mercurial, and SVN rely on.
Color-coded additions, deletions, and unchanged context so the delta is visible in one pass.
Dual line numbers tracking the baseline and the modified document, making it easy to cross-reference with an editor.
Works with any plain text — source code in any language, configuration files, JSON, Markdown, CSV.
Handles large inputs (thousands of lines) in the browser without sending data to a server.
Preserves indentation and trailing whitespace so trivial formatting changes are not hidden.

Frequently Asked Questions

What does each color mean?

Green rows are lines that appear only in the modified side — additions. Red rows are lines that appear only in the baseline side — deletions. Rows rendered with no color are unchanged context that shows up on both sides.

Can I compare files that are thousands of lines long?

Yes. The LCS algorithm is quadratic in the worst case, so files in the tens of thousands of lines may take a couple of seconds to compute. For everyday code-review-sized chunks — a few hundred to a couple of thousand lines — the diff updates instantly.

Does the diff ignore whitespace?

By default the diff is strict — indentation differences, trailing spaces, and mixed tabs/spaces all show up as changes. That is intentional, because invisible whitespace is a common source of real bugs. Normalize whitespace in a separate step if you only want semantic differences.

Does it support any programming language?

Yes. The diff compares text at the line level, so it works for any language, markup, or config format. Syntax highlighting is applied purely for readability and does not affect how differences are computed.

Where is my data sent?

Nowhere. The comparison runs entirely in your browser. That makes the tool safe for internal source code, customer data in CSV form, or any content you are not comfortable pasting into a hosted service.

Code Diff Viewer

Compare two code snippets and visualize differences with line numbers and color-coded highlighting.

Original

Modified

About Code Diff Viewer

All processing happens entirely in your browser. No data is sent to any server, ensuring complete privacy for your source code.

How to Use

Enter original code — Paste the original version of your code in the left panel.
Enter modified code — Paste the modified version in the right panel.
Compare — Click the Compare button to see the diff result with additions, deletions, and unchanged lines highlighted.

Frequently Asked Questions

Q: Can I compare files with thousands of lines?

Yes. The diff viewer handles files up to around 10,000 lines comfortably. For very large files, computation may take a few seconds since the LCS algorithm runs entirely in your browser.

Q: What algorithm is used for diffing?

This tool uses the LCS (Longest Common Subsequence) algorithm, the same approach used by Git and other version control systems for computing diffs.

Q: Does it work with any programming language?

Yes. The diff viewer compares text line by line and works with any programming language or plain text content.

Q: What do the colors mean?

Green indicates added lines (present in modified but not in original). Red indicates removed lines (present in original but not in modified). Gray indicates unchanged lines.

Q: Is there a size limit?

Since all processing happens in your browser, very large files (over 10,000 lines) may take a moment to compute. There is no hard limit.

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HTML Minifier

Compress HTML by removing comments, collapsing whitespace, and optimizing attributes.

JSON Schema Validator

Validate JSON data against JSON Schema Draft-07 with detailed error reporting.

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Introduction

How to Use

Paste the baseline version of your text into the left editor.
Paste the modified version into the right editor.
Hit Compare. The viewer computes the LCS, then paints additions, deletions, and unchanged lines with color-coded markers.
Scan the gutter for line numbers — they track both sides, so you can cross-reference with your source control or editor.
Apply the fixes you agree with, discard the ones you don't, and copy the updated text back into your project.

Examples

Two realistic situations that people diff all the time: a small code change during a refactor, and a configuration tweak during a deploy.

Example 1: Code change during a refactor

A function signature changes to accept an options object instead of positional arguments. The diff makes the two modifications obvious without having to re-read the surrounding lines.

Input

function fetchUsers(limit, offset) {
  const url = `/api/users?limit=${limit}&offset=${offset}`;
  return fetch(url).then((r) => r.json());
}

Output

  function fetchUsers(limit, offset) {
-   const url = `/api/users?limit=${limit}&offset=${offset}`;
+ function fetchUsers({ limit = 20, offset = 0 } = {}) {
+   const url = `/api/users?limit=${limit}&offset=${offset}`;
    return fetch(url).then((r) => r.json());
  }

Example 2: Config change during a deploy

A YAML configuration file has a port change and a new environment variable. The diff flags both lines while confirming the rest of the file is identical.

Input

service:
  name: api
  port: 8080
  env:
    NODE_ENV: production

Output

  service:
    name: api
-   port: 8080
+   port: 8443
    env:
      NODE_ENV: production
+     LOG_LEVEL: info

Target language details

Version assumptions and style choices baked into the generated output. If your runtime is older, you may need to adjust syntax (e.g. drop optional chaining, use `var` instead of `const`).

Language	Version	Output style
JavaScript	ES2017+; works in all evergreen browsers and Node 16+	Functional + async; generated output uses fetch / async-await.
TypeScript	TS 5.x target; interface / type / readonly aware	Interfaces preferred over types for extensibility.

Key Features

Line-by-line comparison using the LCS algorithm — the same approach Git, Mercurial, and SVN rely on.
Color-coded additions, deletions, and unchanged context so the delta is visible in one pass.
Dual line numbers tracking the baseline and the modified document, making it easy to cross-reference with an editor.
Works with any plain text — source code in any language, configuration files, JSON, Markdown, CSV.
Handles large inputs (thousands of lines) in the browser without sending data to a server.
Preserves indentation and trailing whitespace so trivial formatting changes are not hidden.

Frequently Asked Questions

What does each color mean?

Can I compare files that are thousands of lines long?

Does the diff ignore whitespace?

Does it support any programming language?

Where is my data sent?