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Developer Tools

Free, browser-based developer tools for the small but constant tasks that fill a coding day - pretty-printing JSON, decoding a token, encoding a string, testing a regex or converting between data formats. Everything runs locally in your browser tab, so config blobs, payloads and secrets stay on your machine.

No extension to install and no account to create: paste a value, get the result, and copy it straight back into your editor or terminal.

I want to…

Format JSON Beautify, minify and validate Encode or decode Base64 Text and data URIs, both directions Decode a JWT Inspect header and claims locally

Base64 Encoder & Decoder

Encode UTF-8 text to Base64 online or decode Base64 back to UTF-8 and plain text. Runs in your browser with no upload.

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JSON Dialect Detector

Tell whether a file is JSON, JSONC or JSON5 - and convert it to strict JSON.

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Format, validate and diff structured data

Working with APIs means staring at structured text all day. The JSON formatter beautifies, minifies and validates JSON so a one-line API response becomes readable, and the JSON diff viewer highlights exactly which keys and values changed between two payloads. Markup and config get the same treatment with the XML formatter, HTML formatter, CSS formatter, JavaScript formatter and SQL formatter. For arbitrary text, the diff checker shows line-by-line changes between any two snippets.

Encode, decode and inspect

Encoding bugs are everywhere, so the Base64 encoder and decoder and the URL encoder and decoder handle the two most common cases, with bulk URL encode/decode for whole lists and HTML entity encode/decode for markup-safe strings. When you need to read what is inside a token, the JWT decoder splits the header and claims so you can check expiry and audience before trusting it, and the JWT token generator creates signed test tokens. The URL parser breaks a link into its scheme, host, path and query parts.

Convert between data formats

Half of integration work is reshaping data. Move between tabular and tree formats with CSV to JSON and JSON to CSV, between config dialects with JSON to YAML, YAML to JSON and TOML to JSON, and into markup with HTML to JSX for React components. The JSONPath evaluator lets you query a nested object with a path expression rather than scrolling through it by eye.

Generate identifiers and signatures

Need values rather than transformations? The UUID generator produces v4 and other identifiers, the UUID version detector tells you which spec an existing UUID follows, the hash generator and HMAC generator create checksums and signatures, and the Unix timestamp converter turns epoch seconds into a human date and back.

Test, parse and reference

Some tools save you a trip to documentation or a scratch script. The regex tester lets you build and verify a pattern against sample input with live match highlighting, the cron expression parser explains a schedule in plain language, and the user agent parser breaks a UA string into browser, OS and device. Quick lookups live in the HTTP status code reference and the MIME type lookup, while the markdown preview and Tailwind playground give you a quick render surface.

Why client-side dev tools matter

Developer payloads frequently contain secrets - bearer tokens, connection strings, customer records inside a sample response, signing keys. Pasting those into a site that round-trips them through a backend means a third party could log them. Every tool in this category runs as JavaScript in your browser, so the data is processed locally and never uploaded. That also makes the tools fast and usable offline once loaded, which is exactly what you want when debugging on a flaky connection or a locked-down network.

  • Local processing - tokens, payloads and keys stay in the tab.
  • No signup - paste and go, nothing is saved between sessions.
  • Chainable - decode Base64, then format the JSON inside it, then diff it.
  • Reference + transform - lookups and converters in one place.

Frequently Asked Questions

Is it safe to paste a JWT or API payload into these tools?

The developer tools here process input in your browser using client-side JavaScript and do not upload it to ZeroUtil. That is safer than tools that decode tokens server-side, but you should still avoid pasting long-lived production secrets into any web page, and rotate anything that may have been exposed. For sensitive test data, open the network panel and confirm no requests are made.

What is the difference between the JSON formatter and the JSON diff viewer?

The JSON formatter beautifies, minifies and validates a single document so it is readable and syntactically correct. The JSON diff viewer compares two JSON documents and highlights which keys and values were added, removed or changed, which is what you want when comparing API responses or config versions.

Can I convert between JSON, YAML, CSV and TOML here?

Yes. There are dedicated converters for CSV to JSON, JSON to CSV, JSON to YAML, YAML to JSON and TOML to JSON. Each runs in the browser, so you can reshape config files and data exports without uploading them, and you can chain conversions - for example CSV to JSON, then JSON to YAML.

Do the developer tools work offline?

Once the page has loaded, the formatters, encoders, converters and generators run entirely client-side, so most continue to work without a connection. This is possible because none of them depend on a backend request to do their core job, which also keeps them fast on large inputs.

How do I test a regular expression online?

Open the regex tester, enter your pattern and flags, and paste sample text below it. Matches are highlighted live as you edit the pattern, so you can refine a regex against real input before dropping it into code. Like the other tools, it runs in your browser and does not send your test data anywhere.