About JSON Dev Tools
What this site is
JSON Dev Tools is a free collection of browser-based utilities for developers who work with JSON, APIs and data formats every day, plus two reference libraries: a searchable error reference and a set of HTTP status code pages. There are more than 40 tools and references in all, and they are listed at the bottom of this page.
The tools work on what you paste or upload without an account, an upload step, or a server-side component. This page explains how that works and what the site does store or share.
Why I built it
I kept switching between four or five different sites every time I needed to format a JSON response, decode a JWT or convert some CSV. Many of them are slow, and some send what you paste to their servers. That last part matters: you paste a JWT into a decoder to inspect its claims, or a production API response into a formatter, and that data can contain tokens or customer information. Tools that handle sensitive data should process it locally, so I built one place that does.
The site launched in 2026 as a JSON formatter and has grown to more than 40 tools and references.
How the tools work, and what is stored
Every tool is plain JavaScript that runs in your browser tab. Formatting, validating, converting, decoding and hashing all happen on your device, and the site has no backend to send the result to.
- What is saved on your device. The JSON Formatter keeps the text in its input box in your browser's local storage so it survives a reload. It stays on your device, and the Clear button removes it. Preferences such as dark mode are stored the same way.
- What the site does load from elsewhere. The site uses Google Analytics for page-view statistics and carries Google AdSense code to help cover running costs. If you open your browser's Network tab you will see requests to those services, and, on some pages, open-source libraries (such as Ajv, js-yaml and lz-string) fetched from public CDNs. None of those requests contain what you paste into a tool.
- Tools that contact other servers on purpose. The formatter's "Fetch from URL" feature requests the address you type, directly from your browser, and the "Repair" feature downloads the open-source jsonrepair library the first time it is used.
The full details, including share links, cookies and your choices, are in the Privacy Policy.
Who builds it
The site is built and maintained by Pasindu Ishan, a senior software engineer based in Sri Lanka. My day job is designing and operating real-time data streaming systems, mainly on Java, Apache Kafka, Apache Flink and PostgreSQL. It is an independent project, not a venture-backed product, which is why the tools stay simple, fast and free of accounts and paywalls.
That work shapes the site. The Kafka, PostgreSQL, Java and Docker entries in the error reference are the ones closest to what I do every day. The pages on other languages and tools (JavaScript, Python, Go, Rust, TypeScript) are researched from primary documentation, and each one links the official sources it relies on so you can check them.
Tools and references
- Format and inspect JSON: JSON Formatter, JSON Beautifier, JSON Validator, JSON Minifier, JSON Viewer, JSON Diff, Text Diff
- Schemas, queries and test data: JSON Schema Validator, JSON Schema Generator, Multi-sample Schema Generator, Generate JSON from Example, Mock Data Generator, JSONPath Tester
- Convert formats: JSON to CSV, CSV to JSON, JSON to XML, XML to JSON, JSON to YAML, YAML to JSON, JSON to TypeScript, JSON to TOON
- Tokens, encoding and hashing: JWT Decoder, JWT Encoder, Base64, URL Encoder, Hash Generator, UUID Generator, String Escape
- Time, text and CSS: Timestamp Converter, Cron Parser, Regex Tester, chmod Calculator, Color Converter, PX to REM
- Logs and operations: Log Redactor, Error Log Analyzer, Docker Image Optimizer, Deployment Readiness Checker
- References: Error Reference, HTTP Status Codes, HTTP Status Quiz, and the blog
What comes next
The focus now is on improving the existing tools and reference pages rather than adding new ones quickly: fixing mistakes, adding real-world detail from production systems, and keeping the pages accurate as the tools and errors they describe change. Suggestions are welcome.
Get in touch
Questions, corrections or a tool suggestion? Use the Contact page. Reports of mistakes on any page are especially useful, and I read every message myself.