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Text Diff Checker & Line Tools

Compare two texts line by line with colour-coded changes, or clean a list: deduplicate, sort, trim and remove empty lines.

Original vs Changed
Differences
Paste text in both boxes to compare.

About the Text Diff Checker

Comparing two versions of a config file, script or document by eye is error-prone — a single changed character in a firewall rule or registry export is easy to miss. This tool runs a line-based diff (the same longest-common-subsequence approach used by version control systems) and shows removals in red and additions in green with line numbers, entirely in your browser. The whitespace option ignores indentation-only changes, which declutters comparisons of copied-and-pasted configs.

The Line Tools tab covers the everyday list clean-ups that usually get done badly in Notepad: removing duplicate entries from an email list or hostname inventory, sorting, trimming stray spaces from exported data and dropping empty lines. Combined, the two tabs handle most of the “what changed?” and “clean this list up” jobs that come through a help desk.

How to Use This Tool

1
In Compare Texts mode, paste the original text on the left and the changed version on the right.
2
Tick Ignore leading/trailing whitespace when indentation changes would otherwise drown out real edits.
3
Read the colour-coded result: added, removed and changed lines are each marked so the difference is visible at a glance.
4
Switch to Line Tools to clean a list instead: deduplicate, sort A→Z or Z→A, trim whitespace and remove empty lines in one pass.

Common Use Cases

  • ⚙️
    Config file changes. Diff a router config, .conf file or GPO export before and after a change window to prove exactly what changed — and what didn't.
  • 📋
    Policy and document review. Compare two versions of a procedure or contract clause when Word's track changes wasn't used.
  • 🧹
    Cleaning exported lists. Deduplicate and sort a list of hostnames, emails or IPs exported from a spreadsheet before feeding it to a script — pairs naturally with our IP Inventory Planner.
  • 🚨
    Incident forensics. Compare a suspect file against a known-good copy to spot injected lines quickly.
  • 🗃️
    Data reconciliation. Check whether two "identical" exports from different systems really match, line by line.

Typical Uses

  • ⚙️
    Config drift. Diff a switch or firewall config backup against the running config to spot unauthorised changes.
  • 📜
    Script review. Compare the scheduled-task script on a server against the copy in your documentation.
  • 📧
    List hygiene. Deduplicate and sort mailing lists, hostname exports or AD group members before a bulk import.
  • 📑
    Document versions. Check what a colleague actually changed in a shared procedure document.

Frequently Asked Questions

Why do two visually identical lines show as different?
Invisible characters — trailing spaces, tabs vs spaces, or Windows CRLF vs Unix LF line endings. Enable the whitespace option to ignore edge whitespace; if lines still differ, a non-breaking space or zero-width character is the usual suspect.
What's the practical size limit for comparisons?
The diff runs in your browser and handles thousands of lines comfortably. For very large files (say, over 50,000 lines) a desktop tool like WinMerge or diff will be faster, but for configs, lists and documents this is instant.
Why line-based rather than word-based diff?
Configs, scripts, logs and lists — the things IT people diff — are naturally line-oriented, and line diffs stay readable at any size. For prose-level word diffs, a dedicated document comparison tool is a better fit.
Is there a size limit?
The diff algorithm is O(n×m) on line counts, so tens of thousands of lines are fine; hundred-thousand-line files may make the tab pause briefly. All processing stays on your device.
Does “remove duplicates” keep the first or last occurrence?
The first occurrence is kept and later repeats are dropped, preserving the original order of first appearance.