JSON Dev Tools is a free collection of browser-based utilities built for developers who work with JSON, APIs, and data formats every day. Every tool on the site runs entirely in your browser — your data is never sent to a server, never stored, and never shared.
The toolkit covers the full range of JSON and data-format tasks a developer encounters: formatting and validating JSON, comparing two documents, converting between JSON and YAML, XML, CSV, and TypeScript, querying JSON with JSONPath expressions, decoding JWTs, converting timestamps, encoding URLs, hashing strings, generating UUIDs, and more. All from one site, with no signup, no ads on the tools, and no data leaving your device.
I built JSON Dev Tools because I kept switching between four or five different sites every time I needed to format a JSON response, decode a JWT, or convert CSV data. Most of those sites are slow, cluttered with ads, or send your data to their servers. I wanted one fast, clean, private place to do all of these things.
The frustration was specific: you paste a JWT into a decoder to inspect the claims, and you have to trust that the site is not logging your token. You paste a production API response into a formatter, and that response may contain sensitive customer data. Developer tools that handle sensitive data should process it locally — not phone home with it.
The site launched in 2026. It started with a JSON formatter and has grown to include over 20 tools, with more planned based on user requests.
Every tool on JSON Dev Tools is written in plain JavaScript and runs entirely in your browser tab. There is no backend API, no WebSocket connection, and no hidden requests. You can verify this by opening your browser's Network tab while using any tool — you will see no outgoing requests when you paste or process data.
The only external service used is Google Analytics for page view counts, which helps understand which tools are most useful. Analytics is standard and does not receive your tool input data.
The site is built with plain HTML, CSS, and JavaScript — no heavy frameworks, no build step, no dependencies loaded from CDNs that could be compromised. Pages load fast on any connection.
When you paste an API response, a JWT token, a CSV file, or a JSON Schema into any tool on this site, that data stays in your browser. It is processed by JavaScript running in your tab and is never transmitted anywhere. This is a design decision, not just a policy statement — there is no server to send it to.
This matters most for the tools that handle sensitive data: the JWT decoder (tokens can contain user IDs and claims), the JSON formatter (often used with production API responses), and the hash tool (often used with passwords or secrets for verification). All of these work entirely offline once the page loads.
This site was built and is maintained by Pasindu Ishan, a software developer based in Sri Lanka. He works across JavaScript, Python, and web technologies, with a focus on practical tools that solve real developer workflow problems.
Before building JSON Dev Tools, the same frustration with existing tools appeared repeatedly when working with APIs — copy a response, open a new tab, paste, wait for the page to load, deal with ads, wonder if the data is being logged. The solution was to build a single site that does all of these things correctly: fast, private, and without noise.
The current toolkit includes:
The focus is expanding the tool set and improving existing tools based on user feedback. Upcoming additions include a JSON to SQL converter, a regex tester, and a color format converter. The goal is to be the most useful, fastest, and most private developer toolkit available online.
Questions, feedback, or a tool suggestion? Reach out via the Contact page. Bugs and feature requests are always welcome — the site is actively maintained and improves based on real developer needs.