Skip to content
ListDiff

How to compare two lists online

Last updated: 2026-04-13

This guide gives you a repeatable method for comparing two lists accurately, whether your source data is plain text, IDs, usernames, or CSV exports.

Standard 5-step workflow

  1. Open ListDiff tool and fill List A and List B.
  2. Start with default options: case-sensitive off, trim on, ignore-empty on.
  3. Enable split or CSV parsing only when raw lines contain multiple values.
  4. Click Compare lists and inspect A only, B only, and Intersection.
  5. Export the tabs you need as TXT or CSV for downstream work.

Decision matrix for options

  • Use Case sensitive ON only when uppercase/lowercase should be treated differently.
  • Use Trim ON for human-entered or spreadsheet-pasted data.
  • Use Ignore empty ON unless blank lines carry meaning in your process.
  • Use Dedupe items ON for final set comparison; OFF for duplicate diagnostics.

Input -> option -> output example

Input A: u001, u002, u002
Input B: u002, u003
Options: Trim ON, Ignore empty ON, Dedupe items OFF
Output: A only = u001, B only = u003, Intersection = u002, duplicates in A includes u002.

Common mistakes and fixes

  • Low overlap despite similar data: check case and trim settings first.
  • Unexpectedly high item counts: review split delimiters or CSV mode.
  • Confusing stats: remember line badges include blank lines, keys are normalized unique values.

FAQ

What is the fastest way to compare two lists?
Paste or import both lists, keep defaults, run compare, then check A only, B only, and intersection first.

Why do two similar lists show low intersection?
Usually case, spaces, empty lines, delimiters, or CSV mode mismatch.

Related pages

For deeper semantics see Compare Basics. For spreadsheet workflows see Excel paste guide.