Text Diff Checker
Compare two texts and highlight every difference with our free online diff checker. Line-by-line and inline diff views. No signup needed.
See Exactly What Changed Between Two Versions of Any Text
Knowing that two versions of a file differ is far less useful than knowing precisely where they differ and what the specific changes are. Whether you're reviewing a code change without access to a version control diff view, comparing two versions of a contract or legal document, verifying that a configuration deployment actually applied the intended changes, or checking whether two API responses match—the ability to see the exact differences between two text inputs is a tool every developer and writer reaches for regularly.
Our free text diff checker takes two text inputs, runs a line-by-line comparison algorithm, and produces a clearly highlighted output showing which lines were removed, which were added, and which remained unchanged. Lines marked in red are present only in the original (first) version; lines marked in green are present only in the modified (second) version; unmarked lines are identical in both. For inline differences within lines, the tool highlights the specific characters or words that changed rather than flagging the entire line.
How Diff Algorithms Work
The comparison behind our diff tool uses the same algorithmic family as the Unix `diff` utility and tools like Git: the Longest Common Subsequence (LCS) algorithm. The algorithm identifies the longest sequence of lines (or characters, for inline diff) that appear in the same order in both inputs, then marks everything outside that common sequence as either added or removed.
This approach produces the most intuitive diff output—changes are shown where they actually occurred in the text, and unchanged content is clearly preserved with its context. An alternative simpler approach of comparing inputs line by line from the top breaks down quickly when lines are inserted or deleted near the beginning, causing everything after the insertion point to appear as a change. The LCS algorithm avoids this by finding the optimal alignment between the two versions.
Use Cases Where a Diff Checker Is Indispensable
Code Review Without Version Control
Working with code that isn't in a Git repository—a legacy application on a shared host, a quick script someone sent over email, a snippet from documentation—often means you need to compare a modified version against the original without the `git diff` command available. Pasting both versions into our diff checker immediately shows every change highlighted by line and by character, reproducing the clarity of a proper diff view without requiring a repository or command-line access.
Configuration File Verification
After deploying a configuration change to a server, verifying that the live file matches the expected content is a critical sanity check. Capturing the current live file content and comparing it against the expected content using our diff checker immediately highlights any discrepancies—lines that weren't applied, lines that were modified incorrectly, or unexpected additions from a manual edit that wasn't tracked. This is particularly valuable for configuration management where silent drift between expected and actual state can cause subtle production issues.
Document Version Comparison
Legal documents, contracts, technical specifications, and policy documents frequently go through multiple revision rounds where changes need to be precisely tracked. Comparing two versions with our diff checker produces a clear line-by-line view of exactly what was added, removed, or modified between revisions—without requiring Microsoft Word's track changes feature or any other document editing software.
API Response Validation
When debugging API integrations, comparing the actual API response against the expected response reveals exactly where the discrepancy lies. A full JSON response that looks similar but has one incorrect field value or one missing key shows the exact difference clearly in a diff view, rather than requiring manual line-by-line scanning of two long JSON strings.
Database Migration Scripts
Comparing the schema-generating SQL from a migration against the current database schema confirms whether the migration applied completely and correctly. Any discrepancy between the expected post-migration schema and the actual current state shows up immediately in the diff output, making it straightforward to identify missed migrations or manual changes that bypassed the migration system.
Diff Views: Line-Level vs. Character-Level
Line-level diffing marks entire lines as added or removed—appropriate when comparing code or configuration where entire lines are the meaningful unit of change. A function that was rewritten shows the old lines in red and new lines in green, giving you the full context of the change at the line granularity.
Character-level (inline) diffing highlights the specific words or characters within a line that changed—more useful for prose, documentation, and configuration values where a small word change within a longer line is the meaningful unit. "The quick brown fox" versus "The slow brown fox" would highlight "quick" in red and "slow" in green within the same line, rather than flagging the entire line as changed.
Our tool provides both views: the line-level diff gives you the structural overview, and inline highlighting within changed lines shows you the exact character-level changes for lines that were modified rather than entirely replaced.
Completely Private—Your Text Never Leaves Your Browser
The diff checker runs entirely in your browser. No text from either input is transmitted to any server or stored anywhere outside your current session. This makes the tool suitable for comparing proprietary source code, confidential contracts, sensitive configuration files with credentials, or any other text that should not be uploaded to external services. The tool is completely free with no account required.