Free online developer tools
Small utilities for the jobs that interrupt real work — decoding a token, cleaning a spreadsheet export, finding the line where a config file breaks, working out what a cron expression actually does. Each one runs entirely in your browser.
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Search by name or job. Save a favorite, or come back to a recent tool. These page names stay only in this tab's session storage.
- 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.
- JSON and YAML validator Find the exact line, column and likely cause when a config file will not parse.
- CSV cleaner Trim cells, drop empty and duplicate rows, rename headers, keep only the columns you need.
- Diff checker Compare two texts line by line, or two JSON documents by structure and path.
- Time zone converter See one instant in many zones at once, with offsets and daylight saving.
- JWT security checker Audit a token's header and claims for alg none, long lifetimes and personal data.
- Batch filename renamer Build new names in bulk and copy a correctly quoted bash or PowerShell script.
- Responsive viewport preview Render pasted HTML or a URL at phone, tablet and laptop viewport sizes.
- HAR sanitizer Select incident requests, remove unnecessary data, and preview the outgoing HAR.
- AI memory transfer review Review, deduplicate and select text to carry into another assistant.
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Use a tool again
Open a tool to see it here. Saved choices stay only in this tab.
QuietUtils does not upload or store what you paste. Optional favorites and recent tool links store only page names in this tab's session storage; your inputs are not saved. Responsive Preview URL mode contacts the destination you enter, and pasted HTML can load its own remote resources.
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 own processing in JavaScript on your machine. There is no QuietUtils upload endpoint or retention store. Responsive Preview is the exception for network traffic: URL mode contacts the destination, and pasted HTML can load remote resources.
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. The local formatters keep working after they load and the network disconnects. Responsive Preview still needs a network for URL mode and remote resources in pasted HTML.
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?
QuietUtils does not receive or store it. Responsive Preview URL mode sends the address to its destination, and pasted HTML can contact remote resources. The other tools do their work in your tab. Optional favorites and recent tool links store only page names in this tab's session storage; pasted input is not saved.
Can I use these at work, with confidential data?
That is the case the local formatters were built for, and the reason there is no server. Do not use Responsive Preview with confidential HTML that loads remote scripts or other remote resources: those resources can read the previewed content. For the other tools, the data stays on your device. 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 a local formatter and show them the empty request list.
Do the tools work offline?
The local formatters do, once loaded. Responsive Preview cannot load URLs or remote HTML resources offline. Reloading any uncached page also needs a connection.
Why is there no account or sign-in?
Because there is nothing for an account to hold. No work or pasted input 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.