Diff Checker
Compare two texts side by side and highlight every addition, deletion, and change
What is Diff Checker?
Comparing two versions of a file, document, or string to find exactly what changed is one of the most common tasks in software development, content management, and data validation. While version control systems like Git provide diff tools for tracked files, there are countless situations where you need to compare text that is not in a repository — two JSON responses from different API environments, two config files from different servers, a document before and after editing, a string from a log file vs. an expected value, or two SQL queries that should be equivalent but produce different results. Our free Diff Checker performs a line-by-line and character-level comparison of any two text inputs and displays the differences clearly: added lines in green, removed lines in red, and changed lines highlighted with the specific characters that differ. The comparison uses a standard diff algorithm (similar to Unix diff and Git) that minimises the number of differences shown, making it easy to identify the meaningful changes even in large text blocks.
How to Use Diff Checker
- 1
Enter Original and Modified Text
Paste the original (or "before") text into the left panel and the modified (or "after") text into the right panel. The text can be code, JSON, configuration, prose, or any line-based content.
- 2
Compare
Click Compare to run the diff algorithm. Lines that exist only in the original are shown in red (deleted), lines only in the modified version are shown in green (added), and unchanged lines are shown in white.
- 3
Review the Differences
Scan through the highlighted differences. For changed lines, the specific characters that changed within the line are further highlighted so you can see precise character-level edits.
Use Cases
Comparing API Responses from Different Environments
When an API endpoint behaves differently in staging vs. production, the fastest debugging step is comparing the response bodies directly. Paste the staging response in the left panel and the production response in the right, run the diff, and immediately see which fields have different values, which keys are missing, and what structural differences exist.
Reviewing Configuration File Changes
Before deploying a configuration change to a web server, load balancer, or application, compare the current config with the new version here to confirm that exactly the intended changes — and no unintended ones — are present. This is particularly valuable for nginx.conf, apache.conf, docker-compose.yml, and Kubernetes manifests where an unnoticed change can take down a service.
Proofreading Document Revisions
When reviewing edits to a technical document, legal contract, or policy document, paste the original and revised versions here to see precisely which sentences were added, removed, or changed. This is faster and more reliable than reading both versions sequentially and trying to spot differences mentally.
Features
Line-by-Line and Character-Level Diff
Shows both which lines changed and, within those lines, exactly which characters were added or removed — making it easy to spot a single changed variable name or typo.
Colour-Coded Output
Green for added lines, red for removed lines, white for unchanged lines — the standard diff colour convention familiar to any developer.
Side-by-Side and Unified View
Switch between a side-by-side view (original left, modified right) and a unified view (single column showing changes inline) depending on your preference.
Handles Any Line-Based Text
Works equally well for code, JSON, YAML, XML, SQL, Markdown, plain prose, configuration files, and any other text where the meaningful unit of change is a line.
Frequently Asked Questions
This tool uses a variant of the Myers diff algorithm — the same algorithm used by Git, GNU diff, and most version control systems. Myers diff finds the minimum edit distance between two sequences, producing the smallest possible set of insertions and deletions to transform one text into the other. This minimises noise in the diff output and highlights only genuinely meaningful changes.
A line diff compares texts line by line, marking entire lines as added or removed. A character diff then zooms into changed lines and highlights the specific characters that differ within those lines. This tool does both: line-level for the overall structure and character-level for the detail within changed lines — giving you both the big picture and the precise change in one view.
Yes — this tool compares any line-based text. For JSON comparison, it works best when the JSON is pre-formatted (pretty-printed) with consistent indentation, so structurally equivalent values appear on the same lines. Use the JSON Formatter tool first to normalize both JSON inputs, then compare them here for a meaningful structural diff rather than a whitespace diff.
Git diff compares files tracked in a git repository using the same diff algorithm. This tool does the same comparison for any two text inputs — files not in a repository, clipboard contents, API responses, or any text you have access to. It is the right tool when you need a quick comparison outside of a version control workflow.
Unified diff is a standard text format for representing differences, used in patch files and pull request views. It shows the context (unchanged lines), deletions (lines starting with -), and additions (lines starting with +) in a single column. The format was standardised by GNU diff and is what you see in GitHub and GitLab pull request reviews. This tool can display output in unified format as an alternative to the side-by-side view.
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