Free Online Developer Tools
77 tools. Each page explains what the tool does, where your input is processed, and answers the questions people actually ask about it.
JSON & Data
Format, validate, compare and convert structured data.
- JSON FormatterFormat and beautify JSON with configurable indentation and optional key sorting. Runs entirely in your browser.Open tool
- JSON ValidatorCheck whether JSON is valid and get the exact line and column of any syntax error, plus size, key count and nesting depth.Open tool
- CSV to JSON ConverterConvert CSV to JSON with a real RFC 4180 parser that handles quoted commas, embedded newlines and escaped quotes, and keeps 007 and long ids as text.Open tool
- SQL FormatterFormat SQL with one clause per line and indented conditions. Strings, comments and quoted identifiers are never modified.Open tool
- XML FormatterIndent XML, or collapse it to one line. Comments, CDATA and attribute values are never modified, and structural problems are named.Open tool
- JSON Schema GeneratorGenerate a JSON Schema from a sample document. Array elements are merged properly, so a field missing from one element is not marked required.Open tool
- JSON DiffCompare two JSON documents structurally rather than as text. Reports which paths were added, removed or changed, ignoring key order and formatting.Open tool
- JSONPath TesterTest JSONPath queries on your JSON exactly as RFC 9535 defines them, with the Normalized Path of every match and where Jayway and Goessner differ.Open tool
- JSON to CSV ConverterConvert JSON to CSV with nested objects flattened into columns, arrays kept or expanded, spreadsheet formulas escaped, and an optional BOM for Excel.Open tool
- JSON to YAML ConverterConvert JSON to YAML and YAML to JSON with a YAML 1.2 parser that flags yes/no/on values, tab indentation and duplicate keys by line.Open tool
- TOML to JSON ConverterConvert TOML to JSON and JSON to TOML with a TOML 1.0 parser that finds duplicate tables, bad escapes and unquoted strings by line. Runs in your browser.Open tool
- XML to JSON ConverterConvert XML to JSON and JSON to XML, with attributes, repeated elements and namespaces mapped by a documented convention. Runs in your browser.Open tool
- JSON to SQL ConverterConvert a JSON array to SQL INSERT statements and a CREATE TABLE with inferred types for PostgreSQL, MySQL, SQLite or SQL Server, every value escaped.Open tool
- JSON to String ConverterTurn JSON into an escaped string for JavaScript, Java, C#, Python, a JSON string or a .env file, or unescape a stringified JSON string back to JSON.Open tool
- Excel to JSON ConverterConvert an Excel .xlsx file to JSON: one sheet or all of them, the first row as keys, dates as ISO strings. The file is read in your browser, never uploaded.Open tool
- JSON to Excel ConverterConvert a JSON array to an Excel .xlsx file with typed cells: numbers stay numbers, nested objects become columns. Built in your browser; nothing is uploaded.Open tool
- CSV to Excel ConverterConvert CSV to an Excel .xlsx file that keeps 007, phone numbers, long IDs and codes like 1-2 exactly as written. Built in your browser; nothing is uploaded.Open tool
- Excel to CSV ConverterConvert an Excel .xlsx sheet to CSV with the values Excel stores, not its display rounding: UTF-8 with or without a BOM, any delimiter. Nothing is uploaded.Open tool
Encoding & Conversion
Encode, decode and convert between common text formats.
- Base64 Encoder / DecoderEncode text to Base64 or decode it back, with full Unicode support and an optional URL-safe alphabet. Runs in your browser.Open tool
- URL Encoder / DecoderPercent-encode or decode URLs and query parameters, with separate modes for a full URL and a single component.Open tool
- URL ParserBreak a URL into its scheme, host, path, query and fragment, with every query parameter decoded. Warns about credentials and lookalike domains.Open tool
- HTML Entity EncoderEscape HTML entities or decode them back. Handles named, decimal and hexadecimal references, including emoji and other astral characters.Open tool
- Text Escape & UnescapeEscape text for a JSON or JavaScript string, a regular expression, a shell argument or a SQL literal, and unescape it again.Open tool
- Base58 & Base32 EncoderEncode and decode Base58, Base32, Base32hex, Base62 and hex. The encodings behind Bitcoin addresses, IPFS CIDs, TOTP secrets and Tor addresses.Open tool
- Punycode ConverterConvert between Unicode domains and their xn-- punycode form, and detect homograph attacks — names built from lookalike characters to impersonate a domain.Open tool
- Image to Base64 ConverterConvert an image to a Base64 data URI, or decode Base64 back to an image. PNG, JPEG, GIF, WebP, SVG and more, in your browser: nothing is uploaded.Open tool
- Text to Binary ConverterConvert text to binary, hex, octal or decimal bytes and back again. UTF-8 throughout, so é is two bytes, and invalid bytes are reported by offset.Open tool
- Base64 to PDF ConverterDecode Base64 to a PDF or any other file and download it, or encode a file as Base64. The file type is read from its bytes; nothing is uploaded.Open tool
API & Security
Inspect tokens, build requests and generate identifiers.
- UUID GeneratorGenerate random v4 or time-ordered v7 UUIDs in bulk, and decode any UUID’s version and timestamp. Generated locally from a secure random source.Open tool
- JWT DecoderDecode a JWT header and payload, see exactly when it expires, and get warned about alg none and millisecond timestamps. Runs in your browser.Open tool
- Hash GeneratorGenerate MD5, SHA-1, SHA-256, SHA-384 and SHA-512 hashes of any text at once, bit-exact against the published specification vectors, in your browser.Open tool
- Password GeneratorGenerate strong random passwords in your browser using the cryptographic random source, with the real entropy in bits shown for each one.Open tool
- Certificate DecoderDecode a PEM certificate in your browser. Subject, issuer, SANs, validity, key size and SHA-256 fingerprint, with expiry and weak-algorithm warnings.Open tool
- ASN.1 / DER InspectorWalk any ASN.1 DER structure as a tree. Tags, lengths, offsets and decoded values, from PEM, base64 or hex, entirely in your browser.Open tool
- CSP AnalyzerPaste a Content-Security-Policy header to see what each directive does and what it fails to protect. Flags unsafe-inline, wildcards and missing directives.Open tool
- Cache-Control AnalyzerPaste a Cache-Control header to see what a browser and a CDN will each actually do with it, and which directives contradict each other.Open tool
- JWT VerifierVerify a JWT signature against your HMAC secret, in your browser. The secret never leaves your machine, because there is no server to send it to.Open tool
- ULID GeneratorGenerate ULIDs in bulk, monotonic or random, and decode any ULID to its timestamp, randomness and UUID form. Follows the spec, overflow rules included.Open tool
- cURL to CodeConvert a curl command to Python requests, JavaScript fetch, Node.js, Go or PHP. Reads Chrome's Copy as cURL output, $'...' quoting included, in your browser.Open tool
- Bcrypt GeneratorGenerate and verify bcrypt hashes in your browser at any cost from 4 to 31, with a warning when a password runs past bcrypt’s 72-byte limit. Nothing is uploaded.Open tool
- Htpasswd GeneratorCreate htpasswd lines for Apache and nginx basic auth with bcrypt, apr1 or SHA-1, and check a password against an existing line. Runs in your browser.Open tool
- Random String GeneratorGenerate random strings, API keys and tokens from any alphabet or as random bytes in hex or base64url, with no modulo bias and the entropy in bits shown.Open tool
- User Agent ParserParse a user agent string into browser, engine, OS, device and bot, with frozen values marked as frozen and the Client Hints that carry the real ones.Open tool
- HMAC GeneratorGenerate and check HMAC-SHA256, SHA-1, SHA-384 and SHA-512 signatures, with presets for Stripe, GitHub and Slack webhooks. Runs in your browser.Open tool
- TOTP GeneratorGenerate and check TOTP codes from a Base32 secret or an otpauth:// URI, with the previous and next codes and a live countdown. RFC 6238, in your browser.Open tool
- JWT GeneratorCreate and sign JWTs with HS256, HS384, HS512, RS256, PS256 or ES256, with iat and exp helpers and key pairs made in your browser. Nothing is uploaded.Open tool
Programming
Editors, playgrounds and generators for everyday coding.
- Diff CheckerCompare two blocks of text line by line and see exactly what was added, removed or left unchanged.Open tool
- Unix Timestamp ConverterConvert a Unix timestamp to a readable date and back. Detects seconds, milliseconds, microseconds and nanoseconds, and always answers in UTC.Open tool
- Case ConverterConvert names between camelCase, snake_case, kebab-case, PascalCase and CONSTANT_CASE. Handles acronyms, and converts a whole column at once.Open tool
- Cron Expression ParserRead a cron expression in plain English and see exactly when it next runs. Catches the day-of-month and day-of-week trap that fires jobs twice.Open tool
- Color ConverterConvert between HEX, RGB, HSL and HSV, and check WCAG contrast. Uses the published luminance formula, not a brightness average.Open tool
- Number Base ConverterConvert between binary, octal, decimal, hexadecimal and any base up to 36. Exact at any size, including full 64-bit values.Open tool
- Word CounterCount words, characters, sentences and paragraphs, with reading time and the three different character counts that matter in code.Open tool
- CIDR Subnet CalculatorWork out the network, broadcast, mask, wildcard and usable host range for any IPv4 CIDR block. Handles /31 and /32 correctly.Open tool
- Slug GeneratorTurn a title into a clean URL slug. Accented and non-Latin letters survive instead of being deleted, and separators never double up.Open tool
- Lorem Ipsum GeneratorGenerate placeholder paragraphs, sentences or words. A fixed seed produces the same text every time, so mockups stay comparable.Open tool
- Regex TesterTest a regular expression against sample text with live highlighting, capture groups and replacement. A runaway pattern cannot freeze the page.Open tool
- Duration ConverterConvert a duration between milliseconds, seconds, minutes, hours and days. Reads 1h30m, PT1H30M and 01:30:00, and converts to all of them.Open tool
- Line ToolsSort lines alphabetically or naturally, remove duplicates and blanks, trim, reverse and number them. Natural order puts item2 before item10.Open tool
- Semver Range CheckerCheck whether a version satisfies an npm range, and see the range desugared. Explains the prerelease rule that excludes 1.2.4-beta from ^1.2.3.Open tool
- Cron Dialect ConverterConvert a cron expression between Unix, Quartz, AWS EventBridge and Spring. Handles the day-of-week numbering difference that silently reschedules jobs.Open tool
- Discord Timestamp GeneratorMake Discord <t:…> timestamp tags in all nine styles, preview each in any time zone and language, and decode tags you already have. Catches milliseconds.Open tool
- Chmod CalculatorConvert chmod permissions between octal (755), ls -l (rwxr-xr-x) and symbolic (u+x), with setuid, setgid and sticky bits explained in plain English.Open tool
- HTML to JSX ConverterConvert HTML to JSX: class to className, style strings to objects, void tags closed, SVG attributes camelCased, and whitespace kept as React renders it.Open tool
- docker run to ComposeConvert docker run commands to a compose.yaml. Ports, volumes, networks, GPUs and environment mapped to the Compose Specification, with $ escaped.Open tool
- JSON to TypeScriptGenerate TypeScript interfaces, type aliases or a Zod schema from JSON. Array elements are merged, so a key missing from some of them becomes optional.Open tool
- Markdown PreviewPreview Markdown as you type and copy the HTML. CommonMark 0.31.2 with GitHub tables, task lists and strikethrough; raw HTML stays off unless you allow it.Open tool
- JSON to GoGenerate Go structs from JSON with json tags, int64 or float64 per field, pointers for null or missing keys, and time.Time for RFC 3339 dates.Open tool
- JSON to C#Generate C# classes or records from JSON for System.Text.Json or Newtonsoft.Json, with nullable types, required properties and the right number types.Open tool
- CSS MinifierMinify CSS without breaking it, or beautify it with one declaration per line. calc() spacing, descendant selectors and /*! licences survive.Open tool
- JSON to JavaGenerate Java POJOs or records from JSON with Jackson or Gson annotations, boxed types for null, long or BigDecimal numbers and java.time dates.Open tool
- JSON to KotlinGenerate Kotlin data classes from JSON for kotlinx.serialization, Moshi or Gson, with nullable types, null defaults for optional keys and Long or Double.Open tool
- JSON to DartGenerate null-safe Dart model classes from JSON, with fromJson and toJson or json_serializable, doubles read through num, lists and DateTime.Open tool
- PX to REM ConverterConvert px to rem, rem to px, em, pt and every CSS length at any root font size, or a whole stylesheet at once. Media queries and 1px borders handled.Open tool
- IP Address ConverterConvert an IPv4 or IPv6 address to decimal, hex, binary and octal, expand or compress IPv6, and see which range it is in. Flags the forms SSRF filters miss.Open tool
- HTML Formatter and MinifierBeautify HTML with clean indentation, or minify it, changing only whitespace a browser ignores. Inline spacing, <pre> and <textarea> stay as they render.Open tool
- HTML to Markdown ConverterConvert HTML to Markdown for GitHub or CommonMark: tables, task lists and code blocks, with text escaped so it renders back exactly as the HTML did.Open tool