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Best Free Online Tools for Developers

Everything a developer reaches for a dozen times a day, in one place and free. Encode and decode Base64 and URLs, format and convert JSON, YAML, CSV and XML, generate UUIDs and hashes, decode JWTs and timestamps, and build regexes without pasting private data into a sketchy website. Every tool runs entirely in your browser, so tokens, payloads and config never leave your machine. All 83 tools below are free, run in your browser, and need no sign-up.

Base64 Encode / DecodeConvert text to Base64 and decode Base64 back to text instantly in your browser. UTF-8 safe.URL Encoder / DecoderPercent-encode text for URLs or decode encoded URLs instantly. Handles query strings and special characters.UUID GeneratorInstantly generate random v4 UUIDs (GUIDs), one or in bulk. Cryptographically random, copy with one click.Hash Generator (SHA-1 / SHA-256 / SHA-512)Create SHA-1, SHA-256 and SHA-512 hashes from any text instantly in your browser using the Web Crypto API.Unix Timestamp ConverterConvert epoch timestamps to human-readable dates and dates back to Unix time. Supports seconds and milliseconds.JSON MinifierStrip whitespace and newlines to compress JSON into the smallest valid payload for APIs, configs and bundles. Validates as it minifies.JSON ValidatorCheck if your JSON is valid, get the exact error location on failure, and see a pretty-printed version when it parses cleanly.JSON to CSVTurn an array of JSON objects into a clean CSV file with headers, ready for Excel, Sheets or a database import.CSV to JSONParse CSV with a header row into a clean array of JSON objects, handling quoted fields and embedded commas correctly.JSON to YAMLTurn JSON config or API data into clean, readable YAML for Kubernetes, CI pipelines, Docker Compose and app config files.YAML to JSONParse YAML config into clean JSON for APIs, tooling and validation. Handles nested maps, lists, comments and scalars.XML FormatterPretty-print messy or minified XML with clean indentation so nested elements and attributes are easy to read.YAML FormatterNormalize indentation and re-serialize your YAML into clean two-space output by round-tripping it through a parser. Catches errors too.HTML Formatter / BeautifierIndent messy or minified HTML into clean, readable markup with proper nesting so you can scan structure at a glance.CSS FormatterExpand minified CSS into clean, indented rules with one declaration per line so stylesheets are easy to read and edit.JS Formatter / BeautifierExpand minified or one-line JS into readable, indented code with proper brace and block structure.SQL FormatterTurn long, cramped queries into clean, indented SQL with keywords on their own lines so complex statements are readable.HTML Entity Encode / DecodeConvert characters like < > & " to safe HTML entities and back, so text renders literally instead of as markup.Unicode Escape / UnescapeConvert text to backslash-u escape sequences and back, ideal for embedding non-ASCII characters in JSON and source code.Hex to TextDecode hexadecimal byte sequences into readable text and encode text back to hex. UTF-8 safe, handles spaces and 0x prefixes.Binary to TextDecode 8-bit binary into readable text and encode text back to binary. UTF-8 safe, tolerant of spaces between bytes.JWT DecoderDecode a JSON Web Token to inspect its header and payload claims instantly in your browser. Shows expiry in human-readable time.Regex TesterTest JavaScript regular expressions against sample text with live match highlighting, capture groups and flag toggles in your browser.Cron Expression ParserPaste a cron schedule to get a plain-English explanation and the next upcoming run times, all computed in your browser.Cron BuilderPick minute, hour, day, month and weekday from dropdowns to generate a valid crontab expression with a live plain-English preview.Number Base ConverterConvert between binary, octal, decimal and hexadecimal instantly. Type in any base and see all four representations update live.JSON DiffCompare two JSON objects and see added, removed and changed keys with their old and new values, computed entirely in your browser.Text Diff CheckerCompare two blocks of text line by line and see exactly which lines were added, removed or unchanged, computed in your browser.gitignore GeneratorSelect your languages, frameworks and tools to build a solid .gitignore file with sensible defaults, ready to copy into your repo.Chmod CalculatorToggle read, write and execute permissions for owner, group and others to get the octal chmod number and symbolic notation instantly.Subnet / CIDR CalculatorEnter an IP with a CIDR prefix to get the network address, broadcast, usable host range, subnet mask and total hosts.HTTP Status Codes ReferenceSearch all standard HTTP response codes from 1xx to 5xx with their names and meanings. Filter instantly as you type.MIME Types ReferenceSearch common file extensions and their content-type values for setting HTTP headers, uploads and downloads. Filter instantly.ASCII Table ReferenceBrowse all 128 ASCII characters with their decimal, hexadecimal, octal and binary values plus names for control characters.Color Hex to RGBConvert hex color codes to rgb() and back, with a live swatch preview and support for shorthand hex.CSS MinifierStrip comments, whitespace and newlines to shrink stylesheets for faster page loads. Shows how many bytes you saved. Runs in your browser.JavaScript MinifierRemove comments and collapse whitespace to shrink JS for quick inline use. Preserves strings and reports bytes saved.SQL MinifierCollapse a multi-line SQL query into a single compact line by stripping comments and extra whitespace. Great for logs and embedding. Private.JSON String Escape / UnescapeEscape text into a safe JSON string literal, or unescape a JSON string back to raw text. Handles quotes, newlines and unicode. Private.String Length CalculatorCount characters, bytes in UTF-8, words and lines in any string, with and without spaces. Useful for limits and encoding. Private.Placeholder Photo URL BuilderConfigure width, height, grayscale, blur and a seed to generate ready-to-use random placeholder photo URLs for mockups. Private.Base32 Encode / DecodeConvert text to standard RFC 4648 Base32 and decode it back. Handy for TOTP secrets, identifiers and case-insensitive tokens.ROT47 Encoder and DecoderRotate printable ASCII by 47 positions to scramble text, including symbols and digits. Its own inverse, so one button does both.Query String ParserPaste a URL or query string and see every parameter and value in a clean table, with URL decoding and repeated keys handled. Private.HTML Table GeneratorChoose rows and columns, toggle a header row, and get clean, ready-to-paste HTML table markup with a live preview. Runs privately.CSS Box Shadow GeneratorAdjust offset, blur, spread, color and inset with live sliders and preview, then copy the ready-to-use box-shadow rule. Private.Robots.txt GeneratorFree robots.txt generator. Pick which crawlers to allow or block, add disallow paths, crawl delay and a sitemap URL, then copy a valid robots.txt file. Private.UUID v7 GeneratorCreate time-ordered, sortable version-7 UUIDs in bulk. Great for database keys where insertion order and index locality matter. Private.Slugify (URL Slug Generator)Turn any title or phrase into a clean URL-safe slug: lowercase, accents stripped, spaces and symbols collapsed into hyphens. Runs privately.HTML to TextStrip tags and markup from HTML and get the clean plain text content, decoded and readable. All processing stays in your browser.HMAC GeneratorCompute a keyed HMAC over any message with SHA-256, SHA-384 or SHA-512 using the Web Crypto API. Hex output, computed in your browser..env to JSONFree .env to JSON converter. Paste your dotenv KEY=VALUE lines and get a clean, pretty-printed JSON object. Comments and blank lines are ignored. Runs privately.CSS px to rem / em ConverterConvert px to rem and em, or rem and em back to px, with an adjustable root font size. Instant results, computed in your browser.JWT Generator (HS256)Build and sign a JSON Web Token from your payload and a secret using HS256 via the Web Crypto API. Pairs with the JWT decoder. Runs privately.UUID ValidatorPaste a string to check whether it is a valid UUID and see which version (1 through 8) and variant it uses. Instant, private, in your browser.String Case ConverterTurn any text into camelCase, snake_case, kebab-case, PascalCase or CONSTANT_CASE at once. Live, private, in your browser.JSON to XMLTurn JSON objects and arrays into clean, indented XML for legacy APIs, SOAP services, config files and data feeds.XML to JSONParse XML documents into clean, readable JSON with attributes and repeated elements handled correctly in your browser.TSV to CSVTurn tab separated values into proper comma separated CSV, quoting fields that contain commas, quotes or line breaks.CSV to TSVTurn comma separated values into tab separated text you can paste straight into spreadsheets, respecting quoted fields.CSV to Markdown TableTurn CSV data into a clean GitHub flavored Markdown table with aligned columns for READMEs, docs and issues.JSON to TypeScriptGenerate a typed interface from a JSON sample, inferring nested objects, arrays and optional fields automatically.JSON to Go StructGenerate typed Go structs with json tags from a JSON sample, inferring nested types, slices and field names.JSON to PHP ArrayTurn JSON into a valid PHP array literal using short bracket syntax, ready to paste into a config or fixture file.JSON UnescapeTurn an escaped JSON string back into readable text, decoding backslash escapes, quotes, newlines and unicode sequences.JSON to Query StringTurn a JSON object into a URL encoded query string, flattening nested objects and arrays with bracket notation.Query String to JSONParse a URL query string into a clean JSON object, decoding values and grouping repeated keys into arrays.JSON Sort KeysSort every object key alphabetically at all nesting levels for deterministic diffs, cleaner configs and reproducible output.JSON FlattenCollapse a nested JSON object into flat dot notation keys, turning deep structures into a single level map for easy diffing.JSON UnflattenRebuild a nested JSON object from flat dot notation keys, expanding paths and array indices back into real structure.NDJSON to JSON ArrayTurn newline delimited JSON into a single JSON array, parsing each line and reporting any bad rows clearly.JSON Array to NDJSONTurn a JSON array into newline delimited JSON, one compact record per line, ready for streaming and log tools.List to JSON ArrayTurn a plain list of lines into a JSON array of strings or numbers, trimming blanks and optionally deduplicating.CSV Column ExtractorPull a single column out of a CSV file by name or number, with a real parser that respects quoted fields and commas.CSV to SQL InsertTurn CSV rows into ready to run INSERT statements with a header derived column list and safely quoted values.JSON to HTML TableTurn an array of JSON objects into a clean HTML table with a header row and escaped cells, ready to paste anywhere.JSON Path ExtractorPull a value from deep inside JSON using a dot and bracket path like user.tags[0], with clear errors when a path is missing.JSON Stringify ViewerParse and re serialize JSON with a chosen indent, or produce an escaped single string value ready to embed in code.Fixed Width to CSVSplit fixed column mainframe or report text into CSV by specifying column widths, trimming padding from each field.JSON Keys ExtractorList every unique key path in a JSON document, including nested objects and arrays, so you can map or document a payload.JSON to TOMLTurn JSON config into TOML tables and key value pairs for Rust, Python and other tools that read TOML config files.CSV TransposeFlip rows and columns of a CSV so headers become the first column, using a real parser that respects quoted fields.JSON to ENVTurn a flat JSON object into dotenv KEY=value lines, upper casing keys and quoting values that contain spaces.

Frequently asked questions

Are these tools free?

Yes. Every tool in this toolkit is completely free, with no sign-up and no usage limits.

Do these tools work on mobile?

Yes. They run in any modern web browser on phone, tablet or desktop, with nothing to install.

Is my data private?

Yes. These tools run entirely in your browser, so nothing you enter is uploaded to a server.

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