Free online developer tools
Ten small utilities for the jobs that interrupt real work — decoding a token, reformatting a payload, working out what a cron line actually does. Each one runs entirely in your browser.
- JSON formatter Pretty-print, minify and validate JSON, with the position of the first syntax error.
- YAML to JSON Convert a YAML config or manifest into JSON you can paste straight into code.
- JSON to YAML Turn a JSON object into readable YAML for a config file or Kubernetes manifest.
- Base64 encode Encode text to Base64 without a shell round trip or a stray trailing newline.
- Base64 decode Decode a Base64 string back to readable text, padding problems included.
- URL encoder and decoder Percent-encode and decode URLs and query string values, one piece at a time.
- UUID generator Generate version 4 UUIDs in bulk from your browser's own crypto API.
- Unix timestamp converter Convert epoch seconds or milliseconds to a date and back, in local time and UTC.
- JWT decoder Read the header and payload of a JSON Web Token and see when it expires.
- Cron expression parser Explain a cron line in plain English and preview its next five run times.
Nothing you paste into any of these tools is uploaded or stored. The work happens in your browser, and closing the tab is the whole of the cleanup.
Why browser-only matters for developer data
The strings developers paste into online tools are rarely neutral. A JWT is a bearer credential: whoever holds it can act as the user it names until it expires. A YAML manifest carries service account names, internal host names and the shape of a private network. A JSON payload lifted from a bug report usually contains a real customer's email address, order or booking, which turns a quick formatting job into a data transfer nobody recorded.
Most online formatters post that text to a server to do the work. Even where the operator is honest and deletes it immediately, the request has already crossed the network, passed a load balancer and probably landed in an access log — and your employer's data processing agreements say nothing about that host. The safest version of a tool is the one that never receives the data at all.
Every page here does its work in JavaScript on your own machine. There is no upload endpoint to trust, no retention policy to read and nothing to redact afterwards. You can check it in about ten seconds: open the network panel in your browser's developer tools, paste something into a tool and watch the request list stay empty.
They keep working after the network goes
Each page is one HTML file, one stylesheet and one small script — no framework, no web fonts, no analytics. Load a tool, disconnect, and it carries on formatting, decoding and calculating exactly as before. That matters on a locked-down machine, on a plane, or inside an environment where outbound requests are blocked by policy and pasting into a hosted tool is a fireable offence.
It also makes them quick. Once a few kilobytes have arrived there is nothing left to wait for, so a decode happens as you type rather than as a round trip. Bookmark any of them and the page will behave the same next year, because there is no API behind it that can be retired or rate-limited.
Questions people ask
Is any of this sent to a server?
No. Every tool on this site does its work with JavaScript running inside your tab. There is no upload, no logging endpoint and no third-party script analysing what you type. The only network requests a page makes are for the page itself — the HTML, the stylesheet and one script file — and they all happen before you have typed anything. Nothing is written to cookies or local storage either, so there is no history of what you pasted, on our side or on yours.
Can I use these at work, with confidential data?
That is the case they were built for, and the reason there is no server. Because the data never leaves your device, using one of these pages on a customer payload is the same category of act as opening the file in your editor. Do check your own organisation's policy, which may restrict tools by domain rather than by behaviour. If you need to satisfy a reviewer, the whole of each tool is a single readable script — view source, or open the network panel while you use it and show them the empty request list.
Do the tools work offline?
Yes, once the page has loaded. Nothing is fetched afterwards, so you can turn off the network, put the laptop in a room with no signal, or work behind a firewall that blocks everything outbound, and the tools behave identically. Reloading the page needs a connection unless your browser has cached it, so if you know you are heading somewhere without one, open the tools you want before you go and leave the tabs alone.
Why is there no account or sign-in?
Because there is nothing for an account to hold. No work is saved between visits, nothing syncs, and there is no usage quota to enforce, so an account would only collect an email address and give you a password to forget. It would also mean a database of who uses which tool, which is precisely the record these pages exist to avoid keeping. The tools are free, there is no paid tier, and the advertising slots on the page do not depend on knowing who you are.