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Developer tools that never leave your browser
Format JSON, convert timestamps, encode Base64 and more — free, instant, and private by architecture. Every tool runs 100% locally in your browser: there is no server receiving your data, because there is no server at all.
Popular: JSON Formatter & ValidatorBase64 Encoder / DecoderUnix Timestamp Converter
Your frequent tools
Saved only in this browser — nothing leaves your device.
All tools
JSON Formatter & Validator Format, validate and inspect JSON in your browser, with precise error locations and a collapsible tree view. Data formats JSON Checker Check JSON for syntax errors and get the exact line and column of the first problem — validation only, nothing rewritten, nothing uploaded. Data formats JSON to XML Converter Convert JSON to clean, indented XML in your browser — with predictable element naming rules and a report of any key that had to be renamed. Data formats JSON Editor Edit JSON in a syntax-highlighting editor with live error markers, then format, minify and download — entirely in your browser. Data formats JSON to YAML Converter Convert JSON to YAML and YAML back to JSON in your browser — full YAML 1.2 parsing, comments and anchors handled, nothing uploaded. Data formats JSON to CSV / CSV to JSON Converter Turn JSON arrays into CSV tables and CSV files back into JSON — with a live table preview, quoting done properly, all in your browser. Data formats Base64 Encoder / Decoder Encode text to Base64 or decode Base64 back to text — UTF-8 safe, with a URL-safe variant, entirely in your browser. Encoding & tokens URL Encoder / Decoder Percent-encode text for URLs or decode percent-encoded strings — with component and full-URL modes and precise error locations. Encoding & tokens JWT Decoder Decode a JSON Web Token's header and payload, read every claim in plain language, and spot expiry problems — decoding only, never verification. Encoding & tokens Unix Timestamp Converter Convert Unix timestamps to human-readable dates (and back) in UTC and your local time zone, seconds or milliseconds. Network & time Subnet Calculator Calculate network address, broadcast, usable host range, netmask and wildcard from any IPv4 CIDR — with the binary breakdown shown. Network & time What's My IP & Browser Info See the public IP address the internet sees for your connection, its approximate location and ISP — plus the browser, screen and local-network details this device reports. Network & time
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Why local-only tools?
Private by architecture
Most online tools send whatever you paste — production payloads, tokens, internal config — to a stranger's server. Here the page itself is the whole tool: your data never leaves your machine.
Instant, no server round-trip
No upload, no queue, no waiting on a remote backend. Results appear as fast as your device can compute them — even for multi-megabyte files.
Works offline
Load a tool, disconnect from the network, and it keeps working. That is also the easiest way to verify the privacy claim yourself.
Latest guides
Guide How to Validate JSON and Fix the Most Common JSON Errors Trailing commas, single quotes, unquoted keys, stray comments, truncated payloads: the twelve JSON mistakes that cause almost every parse error, how to spot each one, and a workflow that finds them in seconds. Guide Public vs Private IP Addresses: What's the Difference? Your devices live behind one public address with private addresses of their own. How NAT makes that work, the private ranges and their special cases, and how to find each address when you need it. Guide Regular Expressions Cheat Sheet: Patterns You'll Actually Use A compact regex reference plus the ten patterns worth memorising — email, URL, dates, IPv4, hex colours, slugs, UUIDs — each one explained piece by piece, with the traps called out. Guide How DNS Works: From a Domain Name to an IP Address The lookup chain behind every URL: recursive resolvers, root and TLD servers, authoritative answers, TTLs and caching — plus the record types you'll actually meet and the failures they explain.
Essential Developer Resources
The sites developers actually live on — official documentation, the specifications themselves, package registries, quick references and the communities. Hand-picked, and the same list we keep open in our own tabs.
Official Docs
- MDN Web Docs The reference for HTML, CSS, JavaScript and Web APIs — when a browser feature exists, its exact behaviour is documented here. developer.mozilla.org
- Node.js Downloads, release notes and the complete API reference for the Node.js runtime. nodejs.org
- Python The official Python documentation: the language reference, the standard library, and step-by-step how-to guides. docs.python.org
- TypeScript TypeScript documentation and the handbook, plus an in-browser playground for trying code without installing anything. typescriptlang.org
- Google Developers Google's developer documentation hub — web, Android, cloud APIs and the tools around them. developers.google.com
Specs & Standards
- RFC Editor The canonical archive of RFCs — the documents that define how the internet's protocols actually work. rfc-editor.org
- WHATWG The living standards for HTML, DOM, Fetch and other core web technologies, updated as they evolve. whatwg.org
- TC39 / ECMAScript The committee and proposal list behind ECMAScript — where new JavaScript language features are specified. tc39.es
- W3C The World Wide Web Consortium: standards and guidelines for the web platform, from CSS to accessibility. w3.org
- JSON Schema The vocabulary for describing and validating the structure of JSON data, with the current specification drafts. json-schema.org
Platforms & Consoles
- GitHub Where most open-source code lives: repositories, issues, pull requests and CI for millions of projects. github.com
- Google AI Studio Google's browser studio for trying Gemini models, tuning prompts and grabbing an API key to build with them. aistudio.google.com
- Hugging Face The hub for open machine-learning models, datasets and demos — search them, download them, run them. huggingface.co
- npm The registry for JavaScript packages — check a package's versions, readme and weekly downloads before you install it. npmjs.com
- PyPI The Python Package Index: where pip installs from, with every library's releases and documentation links. pypi.org
- Docker Hub The public registry of container images — official images for databases, runtimes and everyday tools. hub.docker.com
Lookup & Reference
- Can I Use Browser support tables for web features — check them before you ship that CSS property or API. caniuse.com
- DevDocs Dozens of API documentations combined into one fast, searchable interface that also works offline. devdocs.io
- HTTP Status Codes Every HTTP status code explained in plain language, each with a link to the spec that defines it. httpstatuses.com
Communities
- Stack Overflow The question-and-answer archive for programming problems — your error message has almost certainly been answered here. stackoverflow.com
- Hacker News A spare, link-driven community where developers discuss launches, tools and the craft of building software. news.ycombinator.com
- Reddit r/programming One of the largest programming communities on Reddit, for articles and discussion about software development. reddit.com
- DEV Community A blogging and discussion community where developers publish tutorials, career notes and tool reviews. dev.to
- Product Hunt A daily leaderboard of new products and developer tools, voted on by its community of makers and users. producthunt.com
Learning
- web.dev Google's guides to building for the modern web — performance, accessibility and web apps, explained with examples. web.dev
- freeCodeCamp Free, full-length courses and certifications for programming, from JavaScript basics through to data science. freecodecamp.org
- JavaScript.info A thorough, modern JavaScript tutorial — plain-language explanations from the fundamentals to advanced topics. javascript.info