Free Online Developer Tools

Format, validate, convert and debug code and data without leaving your browser. Pretty-print or minify JSON, check it for errors, convert between JSON, CSV, XML and YAML, and tidy HTML, CSS and JavaScript. Encode and decode Base64 and URLs, inspect JSON Web Tokens and create SHA hashes.

JSON & CSV

JSON formatterFormat JSON online with 2-space, 4-space or tab indentation. Checks the syntax as you paste and describes any error. Runs locally in your browser, no sign-up.JSON validatorValidate JSON online and see the line and column of the first syntax error. Uses strict JSON.parse rules, checks as you type, and nothing leaves your browser.JSON minifierMinify JSON by removing all spaces, indentation and line breaks outside strings. Validates the input first and shows the output length. Runs in your browser.JSON to CSVConvert a JSON array of objects to CSV with a header row built from every key. Nested values are kept as JSON text. Download a .csv file; nothing is uploaded.CSV to JSONConvert CSV to a JSON array of objects using the header row as keys. Detects comma, semicolon or tab delimiters and handles quoted fields. Runs in your browser.

XML & YAML

XML formatterFormat XML with 2-space, 4-space or tab indentation. Checks the document is well formed first and shows the line and column of any error. Runs in your browser.XML validatorCheck whether XML is well formed and get the line and column of the first error, such as an unclosed tag or a repeated attribute. Runs in your browser.XML to JSONConvert XML to JSON in your browser. Attributes become @-prefixed keys and repeated elements become arrays. Errors show line and column; pick 2, 4 or tab indents.YAML to JSONConvert YAML to JSON with 2-space, 4-space or tab indentation. Expands anchors and aliases, supports multiple documents and shows the line of any error.JSON to YAMLConvert JSON to clean, readable YAML with 2- or 4-space indentation. Strings are quoted only when needed and long lines are never folded. Runs in your browser.

HTML, CSS & JS

HTML formatterFormat HTML with Prettier, including CSS in style tags and JavaScript in script tags. Choose 2 spaces, 4 spaces or tabs. Runs entirely in your browser.HTML minifierMinify HTML by removing comments and collapsing whitespace, while keeping pre, textarea and inline spacing intact. CSS in style tags is minified too.CSS formatterBeautify CSS with Prettier: one declaration per line, consistent spacing and 2-space, 4-space or tab indentation. Reports syntax errors. Runs in your browser.CSS minifierMinify CSS by stripping comments and unneeded whitespace. Keeps /*! license */ comments, strings and url() values intact. Instant, and runs in your browser.JavaScript formatterFormat and beautify JavaScript with Prettier in your browser. Supports modern syntax and JSX, with 2-space, 4-space or tab indentation and clear syntax errors.JavaScript minifierMinify JavaScript with Terser in your browser: removes whitespace and comments, shortens local names and drops dead code. Keeps /*! license */ comments.

Encode & decode

Base64 encoder / decoderEncode text to Base64 or decode Base64 to UTF-8 text in one tool. Accepts URL-safe Base64 and ignores line breaks when decoding. Runs locally in your browser.URL encoder / decoderPercent-encode a query parameter or a full URL, or decode %20-style escapes back to text. Follows encodeURIComponent, encodeURI and decodeURIComponent rules.JWT decoderDecode a JSON Web Token to read its header, payload and iat, nbf and exp dates, and see whether it has expired. Signatures are not verified. Runs locally.Hash generatorGenerate SHA-256, SHA-1, SHA-384 or SHA-512 hashes of text with the Web Crypto API. The hex digest updates as you type, and text is hashed as UTF-8 in your browser.

Generate

UUID generatorGenerate up to 1,000 random version 4 UUIDs at once with crypto.randomUUID. Choose lowercase, uppercase or no hyphens, then copy or download the list.Random string generatorGenerate secure random strings, passwords and tokens from 4 to 512 characters: letters and digits, symbols, hex or digits only. Uses crypto.getRandomValues.

Test & time

Regex testerTest JavaScript regular expressions with live match highlighting, capture groups and match positions. Supports the d, g, i, m, s, u, v and y flags.Unix timestamp converterConvert Unix timestamps in seconds or milliseconds to dates, or ISO dates to epoch time. Shows UTC, local, ISO 8601 and relative time, plus the current timestamp.Date formatterFormat any date or timestamp with tokens like YYYY-MM-DD HH:mm:ss, in local time or UTC. Includes presets, ISO week numbers, day of year and month names.

Formatting for HTML, CSS and JavaScript uses Prettier, and JavaScript minification uses Terser, both loaded in a web worker only when you open those tools. Validators show where the first error is. The UUID and random string generators use your browser’s cryptographically secure random number generator.

Because everything runs locally, you can paste API responses, configuration files and tokens without sending them to a third-party server. The Regex tester runs patterns in a worker with a timeout, so a runaway expression cannot lock up the page, and the Date formatter works in local time or UTC.

Guides

Frequently asked questions

Is it safe to paste API keys or tokens here?

The tools run entirely in your browser and nothing you paste is uploaded or stored. Even so, treat production secrets with care: avoid pasting them on shared computers, and rotate any credential that has been exposed elsewhere.

Does the JWT decoder verify signatures?

No. It decodes the header and payload so you can read claims such as expiry and issuer. It does not check the signature, so a decoded token should never be treated as trusted. Verify tokens on your server with the correct key.

Which hash algorithms are available?

The Hash generator creates SHA-1, SHA-256, SHA-384 and SHA-512 digests using the browser’s Web Crypto API. MD5 is not included. For new work, prefer SHA-256 or stronger; SHA-1 is only suitable for legacy checksums.

How do I find the error in invalid JSON?

Paste the JSON into the JSON validator or JSON formatter. If it cannot be parsed, the tool shows the error message with the line where it occurred. Common causes are trailing commas, single quotes and unquoted keys.

Are the generated UUIDs unique?

The UUID generator creates random version 4 UUIDs with a secure random source. With 122 random bits, the chance of a collision is negligible for practical purposes, so they are safe to use as identifiers in databases and APIs.