// Free Online Developer Tools (58 tools, by category)
Browser-based utilities for developers and power users. No sign-up, no install, and your input never leaves the page.
The tools below are grouped the way the work tends to be grouped: addressing and permissions together, token handling together, the conversions that interrupt a meeting together. If you already know what you need, the cards link straight to it. If you are not sure, the category pages are written to be read rather than skimmed, and each one covers the mistakes that area invites.
What every tool here has in common is that it runs entirely in your browser. There is no upload step and no endpoint receiving your input, which is what makes it reasonable to paste a production token, a real crontab line or an internal architecture diagram into one of them. It also means the tools stay usable on a restricted network, and keep working once the page is loaded even if the connection drops.
Data Formats 10
Convert and format JSON, YAML, CSV, XML and more
JSON Formatter
Format messy JSON with 2-space, 4-space or tab indentation, or minify it, and see syntax errors with the position they occur. Runs entirely in your browser.
JSON Diff
Compare two JSON documents structurally, so key order and indentation are ignored. Match array elements by id, and export the result as a JSON Patch.
YAML ⇄ JSON Converter
Convert YAML to JSON and JSON back to YAML in your browser. Handles nested maps, sequences, block scalars and inline flow style, with a key count.
TOML ⇄ JSON Converter
Convert TOML configuration to JSON and back in your browser. Handles tables, nested keys, arrays and the usual scalar types, with selectable indentation.
CSV ⇄ JSON Converter
Convert CSV to a JSON array of objects and back again, choosing comma, tab or semicolon as the delimiter. Quoted fields and embedded commas are handled.
TSV ⇄ JSON Converter
Convert tab-separated data to a JSON array of objects and back. Paste straight from a spreadsheet, with no quoting rules to get wrong.
XML ⇄ JSON Converter
Convert XML to JSON and back in your browser. Attributes become @name, text nodes become #text, and repeated sibling elements become arrays.
JSON Schema Generator
Paste a JSON sample and get a JSON Schema describing it, with types, nested objects and arrays inferred. Ready to paste into OpenAPI or a validator.
JSON to TypeScript
Paste JSON and get TypeScript interfaces or type aliases, with nested objects extracted into their own named types and array element types inferred.
JSONPath Finder
Paste JSON and get every path in it listed in dot or bracket notation, with a depth limit and a filter. Click any path to copy it.
Text 10
Character counting, case conversion, sorting and replacing
Character Counter
Count characters with and without spaces, plus words, lines, paragraphs and UTF-8 bytes, updating as you type. Nothing you paste is uploaded.
Text Statistics
Analyse text in your browser: character counts by script, the most frequent characters and words, whitespace totals and an estimated reading time.
Case Converter
Convert text between camelCase, PascalCase, snake_case, kebab-case, CONSTANT_CASE, dot.case, Title Case, uppercase and lowercase, all at once.
Text Sorter
Sort lines alphabetically, remove duplicates, trim whitespace and drop blank lines in one pass. Runs in your browser with nothing uploaded.
Bulk Text Replacer
Apply up to ten find-and-replace rules in one pass, with optional regular expressions and case-insensitive matching, plus presets for common cleanups.
Dummy Text Generator
Generate Lorem Ipsum or Japanese placeholder text by paragraph, sentence or word. Useful for layout testing where real copy is not ready yet.
Full-width ⇄ Half-width Converter
Convert full-width letters, digits, symbols and katakana to half-width and back. Essential for cleaning data exported from Japanese systems.
Unicode Converter
Inspect any text character by character to see its code point, UTF-8 bytes and escape forms, or convert text to and from JavaScript, HTML and CSS escapes.
ASCII Art Generator
Turn text into ASCII art banners using ten FIGlet fonts. Ideal for README headings, terminal startup banners and CLI splash screens.
Emoji Search
Search emoji by keyword or browse by category, and copy one with a click. Recently used emoji are remembered in your browser for next time.
Encoding 5
Base64, URL encoding, HTML escaping and image Data URIs
Base64 Encoder / Decoder
Encode and decode Base64 in your browser: UTF-8 text, emoji, Basic auth headers and JWT segments. Nothing you paste is uploaded or logged.
URL Encoder / Decoder
Percent-encode and decode URLs in your browser, with both encodeURI and encodeURIComponent. Handles spaces, plus signs, emoji and non-Latin text.
URL Parser
Paste a URL and see its scheme, host, port, path, query parameters and fragment separated out, with every parameter listed as a decoded key and value.
HTML Escape / Unescape
Escape HTML special characters to entities and convert them back, in your browser. Covers the five characters that matter for XSS safety and display.
Image to Base64
Drop an image to get its Base64 string and a ready data: URI, or paste a data URI to preview and download the image. PNG, JPEG, GIF, WebP and SVG.
Security 5
Hashing, JWT decoding, password generation and CORS
Hash Generator
Generate SHA-1, SHA-256, SHA-384 and SHA-512 hashes from text, all at once, in your browser. Uses the Web Crypto API, and nothing you type is uploaded.
JWT Decoder
Decode JSON Web Tokens instantly: view header, payload and signature, turn exp/iat/nbf into dates and spot expired tokens. Runs entirely in your browser.
Password Generator
Generate strong random passwords in your browser using crypto.getRandomValues. Choose length, character sets and how many to produce, with an entropy readout.
CORS Header Generator
Build the Access-Control response headers for your API from a form: allowed origin, methods, headers, exposed headers, credentials and max-age.
CSP Generator
Build a Content-Security-Policy from a form, with warnings for settings that defeat it. Outputs the header, a Report-Only version, a meta tag and NGINX config.
Code 4
Regex, SQL formatting, cron parsing and diff
Regex Tester
Test a regular expression against your text and see every match highlighted in place, with capture groups and positions listed. Runs in your browser.
SQL Formatter
Turn a single-line SQL query into indented, readable SQL with keywords aligned. Handles SELECT, JOIN, WHERE, GROUP BY and subqueries, in your browser.
Cron Expression Parser
Decode any cron expression into plain English and list the next 5, 10 or 20 run times. Presets, field guide and validation. Runs entirely in your browser.
Diff Checker
Compare two pieces of text and see exactly what was added, removed and left alone, by line or by character. Runs in your browser with nothing uploaded.
Design 8
Colors, gradients, shadows and image/SVG optimization
Color Converter
Convert a colour between HEX, RGB and HSL, with alpha support and sliders for hue, saturation and lightness. Everything updates live in your browser.
CSS Gradient Generator
Build a CSS gradient visually: linear, radial or conic, with as many colour stops as you need and a live preview. Copy the rule with one click.
Box Shadow Generator
Build a CSS box-shadow visually with offset, blur, spread, colour, alpha and inset, stacking multiple layers. Copy the rule with one click.
HTML Live Preview
Write HTML, CSS and JavaScript and see the result render as you type. No account, no saving, no setup — just a scratchpad that runs in your browser.
Markdown Preview
Write Markdown and see the rendered result as you type, including GFM tables, fenced code blocks, quotes and lists. Copy the HTML with one click.
Mermaid Preview
Write Mermaid code and preview flowcharts, sequence, class, state, ER, Gantt and pie diagrams live. Export SVG or PNG. Runs entirely in your browser.
SVG Optimizer
Remove the metadata Illustrator and Inkscape leave behind, strip comments and empty groups, and see the size saved, with a live preview of the result.
Image Optimizer
Compress and resize JPEG, PNG and WebP images entirely in your browser. Adjust quality, set dimensions with aspect ratio lock, and see the size saved.
Network 7
Subnets, chmod, HTTP status codes, curl and redirects
Subnet Calculator
IPv4 subnet calculator: enter an IP and CIDR prefix to get subnet mask, wildcard mask, network, broadcast, usable range and host count. In your browser.
chmod Calculator
Convert Linux chmod permissions between octal (755, 644) and rwx with checkboxes, an ls -l preview, setuid/setgid/sticky bits and presets. In your browser.
HTTP Status Codes
A searchable reference to HTTP status codes, each with what it means, the common causes, and what to actually do about it. No sign-up, no lookup delay.
cURL Converter
Paste a curl command and get ready-to-run fetch, Axios, Python requests, Go, PHP or Ruby code. Works with Copy as cURL. Runs entirely in your browser.
HTTP Header Analyzer
Paste response headers and get each one explained, with warnings for weak security settings and a list of the key security headers you are missing.
User-Agent Parser
Paste a User-Agent string to identify the browser, rendering engine, operating system and device, including modern AI crawlers such as GPTBot and ClaudeBot.
.htaccess & Nginx Redirect Generator
Generate Apache .htaccess and Nginx redirect rules from a form: force HTTPS, normalise www and trailing slashes, add 301s, with loop and chain warnings.
Utilities 9
QR codes, UUIDs, Unix timestamps, dice probability and more
QR Code Generator
Turn text, a URL, Wi-Fi details or contact information into a QR code and download it as PNG or SVG. Generated in your browser, with no tracking redirect.
UUID Generator
Generate version 4 UUIDs in your browser using crypto.randomUUID. Produce one or many at a time and copy them individually or all at once.
Unix Timestamp Converter
Convert a Unix timestamp to a readable date and a date back to a timestamp, in seconds or milliseconds, with the current epoch time always on screen.
Time Zone Converter & World Clock
Convert any date and time across 45 cities, watch a live world clock with daylight saving handled automatically, and plan meetings in your browser.
Number Base Converter
Convert a number between binary, octal, decimal and hexadecimal at once. Handles arbitrarily large values with BigInt and negative numbers too.
Byte Converter
Convert a size between bytes, KB, MB, GB, TB and PB at once. Uses 1024 as the step, the convention operating systems and developers actually use.
Unit Converter
Convert length, weight, temperature, area, volume, speed, time, angle, pressure and energy across 80+ units at once. Runs entirely in your browser.
HTML Table ⇄ CSV
Convert an HTML table into CSV, or turn CSV into a clean HTML table. Includes a rendered preview and a header row toggle. Runs in your browser.
Dice Probability Calculator
Work out the exact probability of rolling a given total with any number of dice, with a full distribution, cumulative odds and a roll simulator.
// Frequently asked questions
- How do I find the right tool?
- Use the category strip at the top of this page if you know roughly what area you are working in, or scan the cards, which each state what the tool does in one line. Every category also has its own page explaining what the tools in it are for and what tends to go wrong in that area.
- Do these tools work offline?
- Yes, once the page has loaded. The logic is client-side JavaScript that is already in the browser, so a tool keeps working if you lose your connection. What it cannot do is load a page you have not visited yet.
- Is there a rate limit or a usage cap?
- No. Because nothing is processed on a server there is no quota to enforce. Convert as many values as you like.
- A tool I want is not listed. Where is it?
- The English edition currently covers 58 of the 59 tools on the site, and is being extended. The remaining tools exist in the Japanese edition and work identically there; only the surrounding explanation is in Japanese.