PureDiff — Compare Files Securely in Your Browser

PureDiff is a zero-upload file comparison tool that runs entirely in the browser. Paste two blocks of text, upload two files, or mix both—see exactly what changed, line by line. Your data never touches a server.

The Privacy Problem with Most Diff Tools

Paste a config file, a contract, or internal code into a typical online diff tool and you've sent that data to someone else's server. Most tools don't advertise this. A few log it. None give you a guarantee they won't.

PureDiff solves this at the architecture level: there is no server-side processing. The diff algorithm runs in your browser tab. Close the tab and the data is gone.

How It Works

Upload or Paste

You have two panels — left and right. Each accepts:

• Pasted text — paste directly from clipboard
• Uploaded files — drag-and-drop or click to browse
• Any plain-text format — code, config, JSON, YAML, Markdown, CSV, logs

No file size limits beyond your browser's memory. No format restrictions.

Read the Diff

PureDiff highlights every change between the two inputs:

• Added lines — shown in green
• Removed lines — shown in red
• Unchanged lines — displayed in context

Choose between two layout modes:

• Side-by-side — the two files rendered in parallel columns, changes aligned
• Inline — a single column with additions and deletions interleaved

Both views support scrolling through long files with the diff anchored to the first change.

Whitespace Control

Whitespace differences can be noise or signal depending on context. PureDiff lets you toggle Ignore Whitespace so trailing spaces, mixed indentation, and blank-line differences don't clutter your results when you don't need them.

Who It's For

PureDiff was built for anyone who needs to compare text quickly and privately:

• Developers reviewing config changes, migration scripts, or generated output before shipping
• Security teams auditing changes in sensitive files where upload is out of the question
• Legal and compliance comparing contract drafts where confidentiality matters
• Writers and editors tracking revisions between document versions
• Data engineers spot-checking CSV or JSON output against expected values

If you've ever pasted anything sensitive into an online diff tool and immediately regretted it, PureDiff was built for that moment.

Technical Details

PureDiff is built on:

• Next.js (App Router) — fast initial load, static export capability
• TypeScript — type-safe diff logic with no runtime surprises
• Client-side diff engine — no WebAssembly, no workers required for typical file sizes
• Zero external API calls — the network tab stays clean

The diff algorithm computes the longest common subsequence (LCS) to find the minimal edit distance between the two inputs. Performance is linear for typical source files and degrades gracefully on very large inputs.