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Developer Tools
JSON formatter, XML/YAML/CSV converters, Base64 & JWT decoder, SQL formatter, and 25+ more. Lightning-fast, privacy-first — everything runs in your browser.
Converters
XML → JSON
Convert XML data to JSON format instantly. Supports attributes, nested elements, and preserves data types.
JSON → XML
Convert JSON data to XML format with proper formatting and structure.
YAML → JSON
Convert YAML documents to JSON format with proper type inference.
JSON → YAML
Convert JSON data to clean, human-readable YAML format.
JSON → TOON
Convert JSON to TOON (Token-Oriented Object Notation) — a compact format that cuts LLM prompt tokens by up to 40%.
TOON → JSON
Convert TOON (Token-Oriented Object Notation) back to formatted JSON, and validate it while you are at it.
JSON → JSONL
Convert a JSON array to JSONL (JSON Lines / NDJSON), one record per line — the format OpenAI and Anthropic fine-tuning requires.
JSONL → JSON
Convert JSONL (JSON Lines / NDJSON) into a formatted JSON array, with the exact line number reported for any record that fails to parse.
HTML → Pug
Convert HTML markup to clean Pug (Jade) template syntax.
Pug → HTML
Compile Pug (Jade) templates to standard HTML markup.
JSON → Schema
Generate a JSON Schema definition from a sample JSON document.
JSON → ION
Convert JSON data to Amazon ION text format.
JSON → M3U
Convert JSON data to M3U/M3U8 playlist format. Supports music playlists and IPTV streams with extended attributes.
Text → JSON
Convert key-value text mappings to JSON. Supports tab, equals, colon, and arrow separators.
JSON → CSV
Convert JSON arrays or objects to CSV format for spreadsheets and data analysis.
CSV → JSON
Convert CSV data to a JSON array of objects. Auto-detects data types.
JSON → TypeScript
Generate TypeScript interfaces from JSON data. Supports nested objects and arrays.
JSON → Go
Generate Go structs with JSON tags from sample JSON data.
MD → HTML
Convert Markdown documents to clean, semantic HTML markup.
HTML → MD
Convert HTML markup to clean, readable Markdown syntax.
Formatters
JSON Format
Format, beautify, and validate JSON data with customizable indentation.
XML Format
Format and beautify XML documents with proper indentation.
HTML Format
Format and beautify HTML documents with proper indentation and structure.
CSS Format
Format and beautify CSS stylesheets with proper indentation.
JS Format
Format and beautify JavaScript code with proper indentation and structure.
SQL Format
Format, beautify, and indent SQL queries with uppercase keywords.
Decoders & Encoders
Base64
Encode text to Base64 or decode Base64 strings back to text.
JWT Decode
Decode and inspect JWT (JSON Web Token) headers, payloads, and claims.
URL Encode
Encode text for URLs or decode percent-encoded strings back to readable text.
HTML Entities
Encode special characters as HTML entities or decode HTML entities back to text.
Utilities
JSONL Validator
Validate a JSONL file line by line and check every record against the OpenAI and Anthropic chat fine-tune schema before you upload it.
Token Counter
Count exactly how many tokens your text costs with the real OpenAI tokenizers — o200k_base and cl100k_base — not a character estimate.
llms.txt Generator
Turn a sitemap.xml or a list of URLs into an llms.txt skeleton, ready to describe your site to AI assistants.
Hash Gen
Generate SHA-256, SHA-1, and SHA-512 hashes from any text input.
Base Convert
Convert numbers between decimal, hexadecimal, binary, and octal formats.
Compare
Compare two text files or code snippets side by side with highlighted differences.
Why Developers Love CodeMash
Built by developers, for developers. Every tool is designed to save you time while keeping your data safe.
Privacy First
Your data never leaves your browser. No tracking, no storage, no cookies.
Lightning Fast
Client-side processing means instant results. No server round-trips needed.
Free Forever
All tools are completely free with no usage limits. No sign-up required.
Works Everywhere
Responsive design works on desktop, tablet, and mobile. No app required.
Free Online Developer Tools — JSON Formatter, Converters & More
CodeMash is your all-in-one suite of free online developer tools. Whether you need a JSON formatter to beautify minified JSON, an XML to JSON converter to transform data, or a JWT decoder to inspect token claims — our 25+ tools handle it all instantly in your browser with zero setup, no sign-up, and complete privacy.
Convert Between Data Formats
Seamlessly convert between popular data formats: XML to JSON, JSON to XML, YAML to JSON, JSON to YAML, JSON to CSV, CSV to JSON, and more. Generate TypeScript interfaces from JSON, Go structs from JSON, or JSON Schema from sample data to validate your APIs. Convert between Markdown and HTML for documentation, and HTML to Pug (Jade) for Node.js template engines.
Format & Beautify Code Online
Clean up minified or messy code with our formatting tools: JSON formatter & validator, XML formatter, HTML beautifier, CSS formatter, JavaScript beautifier, and SQL formatter. Customize indentation (2 or 4 spaces), toggle between pretty-print and minified output, and get perfectly formatted code every time. Our SQL formatter supports MySQL, PostgreSQL, and standard SQL with automatic keyword uppercasing.
Encode, Decode & Hash
Base64 encode and decode strings with full Unicode support. Decode JWT tokens to inspect headers, payloads, and claims — a privacy-first alternative to jwt.io. URL encode and decode text for safe query parameters. Encode and decode HTML entities to prevent XSS. Generate SHA-256, SHA-1, and SHA-512 hashes using the Web Crypto API. Convert between hex, decimal, binary, and octal number systems.
Compare Text & Code
Use our diff checker to compare two text files or code snippets side by side with highlighted additions, deletions, and changes. Perfect for code reviews, debugging, and tracking configuration changes.
100% Private — Your Data Never Leaves Your Browser
Every tool on CodeMash runs entirely in your browser using client-side JavaScript. Your data is never sent to any server, never logged, and never stored. This makes CodeMash the safest choice for handling sensitive data like API keys, JWT tokens, configuration files, and proprietary code. No cookies, no tracking, no accounts — just fast, private developer tools that work.