About diff.quest

diff.quest is a free, open suite of comparison and formatting tools built for developers, writers, and anyone who works with structured data. Every operation runs entirely in your browser. No sign-ups, no uploads, no tracking. Curious about the algorithms? Read the technical deep-dive.

What You Can Do

Compare & Diff

Paste two versions of a document and instantly see what changed, down to the character or token level. Every diff tool supports both Split (side-by-side) and Unified views.

• Text Diff : Free-form prose, Markdown, code, logs. Character-level precision.
• JSON Diff : Compares JSON with optional key sorting to ignore reordering.
• YAML Diff : Semantic comparison with optional key sorting.
• TOML Diff : Normalized TOML comparison with consistent formatting.
• XML Diff : Structure-aware XML comparison.
• Key=Value Diff : For .env, .properties, and similar config files.
• CSV Diff : Tabular data comparison with auto-detected delimiters.
• Markdown Diff : Token-level comparison for Markdown documents, preserving formatting intent.
• Image Diff : Perceptual hashing plus five pixel-level visualization modes.

Format & Beautify

Clean up messy data into readable, consistently indented output. All formatters validate syntax before formatting.

• JSON Formatter : Pretty-print JSON with 2-space indentation.
• XML Formatter : Indent and normalize XML documents.
• YAML Formatter : Reformat YAML with consistent structure.
• TOML Formatter : Normalize TOML with proper table spacing.
• CSV Formatter : Align CSV columns for readable table display.
• JSON Minifier : Strip whitespace for compact payloads.

Validate

Catch syntax errors and structural issues before they reach production.

• Key=Value Validator : Detects duplicate keys, missing values, mixed quote styles, and 15+ other issues in .env files. Includes auto-fix with configurable rules.
• Markdown Validator : Validates YAML frontmatter in .md files. Catches syntax errors, duplicate keys, and malformed delimiters. Includes auto-fix with configurable formatting rules.

Analyze

Understand your text without comparing it to anything.

• Text Analytics : Character, word, sentence, and paragraph counts. Entropy analysis and character frequency breakdown.
• Tokenizer : See how text splits into tokens across different LLM encodings (GPT-4o, GPT-4, GPT-3.5). Useful for understanding token budgets and NLP pipelines.

Privacy-First Architecture

Most online diff tools process your data on their servers, storing and potentially logging sensitive information. diff.quest was built to eliminate that risk entirely.

• 100% Client-Side Processing: All diffing, formatting, validation, and analysis runs in Web Workers on your machine. Your data never leaves your browser. There are no API calls, no server-side processing, and no network requests for any user operation.
• Zero Server Storage: We don't store, log, transmit, or cache your data. The server only delivers the static application files.
• No Tracking: No analytics scripts, no cookies, no fingerprinting. We don't know who you are or what you paste.
• Fully Offline: diff.quest is a Progressive Web App (PWA). Once loaded, it works without an internet connection. Install it from your browser for instant access.

How It Works

Under the hood, diff.quest uses Web Workers to run all CPU-intensive work (parsing, diffing, image hashing) off the main thread. This keeps the interface responsive even with large files. The diffing engine uses the Myers Difference Algorithm (the same algorithm behind git diff) with two granularity modes: character-level for prose and token-level for structured data. Image comparison uses perceptual hashing (pHash) and pixel-level analysis.

For a detailed walkthrough of the algorithms, view modes, normalization pipeline, and image comparison techniques, see the Learn page.

Need to Edit, Not Just Compare?

Most diff tools stop at showing you what changed. When you need to go further and actually resolve those changes, check out our sister project: editor.diff.quest .

It is a full in-browser code editor built on the same privacy-first foundation. No server, no uploads, no tracking. You can edit both sides live, merge changes selectively, and save results to your machine. Use diff.quest to understand what changed, then jump to editor.diff.quest to act on it.

Get Started

Pick any tool from the navigation above, or start with the Text Diff tool to compare two documents right now. Every tool is free, requires no account, and works instantly in your browser.