Developer tools that keep your data in your browser
Format and compare JSON, decode JWTs, test regexes, encode URLs and Base64, convert timestamps, and generate Flutter code from JSON, colours and SVG. Free, fast and without accounts.
Tools
11 tools found
- JSONJSON Formatter & ValidatorPretty-print, validate and repair JSON, including Flutter log output.
- JSONJSON DiffCompare two JSON documents and list every difference by path.
- JSONJSON to DartTurn a JSON response into null-safe Dart classes for Flutter apps.
- FlutterFlutter Color ConverterConvert hex and CSS colours to Flutter Color code and back.
- FlutterSVG to Flutter CustomPainterTurn an SVG icon or path into Flutter CustomPainter code.
- FlutterFlutter BoxShadow GeneratorDesign BoxShadows or convert CSS box-shadow to Flutter.
- AuthJWT DecoderRead a JWT's header, claims and expiry without sending it anywhere.
- TextRegex TesterTest a JavaScript regex with highlighted matches, groups and replace.
- EncodingURL Encoder & DecoderPercent-encode or decode text and inspect URL query parameters.
- EncodingBase64 Encoder & DecoderEncode and decode Base64 or Base64URL text and files.
- TimeUnix Timestamp ConverterConvert epoch seconds or milliseconds to UTC/local dates and back.
For Flutter developers
Generated Dart is checked on a real Flutter SDK before it is published, and each page says which version.
- JSON to DartTurn a JSON response into null-safe Dart classes for Flutter apps.
- Flutter Color ConverterConvert hex and CSS colours to Flutter Color code and back.
- Flutter BoxShadow GeneratorDesign BoxShadows or convert CSS box-shadow to Flutter.
- SVG to Flutter CustomPainterTurn an SVG icon or path into Flutter CustomPainter code.
Why use these tools
Processed on your device
Tools run in JavaScript in your browser. Tokens, JSON and other input are not uploaded or stored by this site.
Instant results
Output updates as you type. No sign-up, no waiting for a server round trip.
Precise feedback
Exact error locations, explicit warnings about precision loss and expiry, and documentation on every page.
Guides
All guides- How to Debug API Responses: A Practical WorkflowA step-by-step workflow for failing API calls: status codes, headers, HTML-instead-of-JSON errors, response diffs, JWTs, timestamps and URL encoding.
- How to Compare Two JSON FilesWhy text diffs mislead for JSON, how key order, array order, null and type changes should be treated, and how to compare JSON with jq, Node.js and Python.
- URL Encoding Explained with Practical ExamplesHow percent-encoding works, encodeURIComponent vs encodeURI, + vs %20 and double encoding, with tested JavaScript, Python and curl examples.
- JWT Decoding vs. Signature VerificationWhy anyone can read a JWT, what decoding does and does not prove, and how servers should actually verify tokens.
- How to Format and Validate JSON (jq, Python, Node)Pretty-print, minify and sort JSON, see how formatters change numbers, and validate JSON with tested jq, Python and Node.js commands, in code and in CI.
- Common JSON Syntax Errors and How to Fix ThemTrailing commas, single quotes, unquoted keys, raw line breaks and other mistakes that make JSON.parse fail, with fixes.
- How to Monitor an API Endpoint for FreeWhat to check beyond uptime, tested curl, jq and Node.js check scripts, and the free tiers of UptimeRobot, Better Stack, Checkly and Uptime Kuma.
- Flutter JSON Errors: "is not a subtype" ExplainedFix Flutter and Dart JSON errors: List<dynamic> is not a subtype of Map<String, dynamic>, int is not a subtype of double, Null errors and FormatException.
- Parse DateTime from JSON in Flutter and DartParse API dates in Dart: ISO strings with and without offsets, FormatException: Invalid date format, Unix seconds vs milliseconds, and toIso8601String.
- Convert Local Time to UTC Without DST BugsConvert local date-times and zone names to UTC in JavaScript, Python and SQLite: offsets vs time zones, strings without offsets, DST gaps and overlaps.
- Unix Timestamps Explained: Seconds vs MillisecondsWhat epoch time is, how to tell seconds from milliseconds, and how to convert timestamps to UTC correctly in common languages.
A note on privacy
Running in the browser means your input stays on your device, but it does not make sensitive data safe to paste anywhere. Read the privacy policy for exactly what this site does and does not collect.