guest@retro-tools:~$ ./welcome.sh
RETRO WEB TOOLS Free online developer tools
Convert cURL commands, parse cron expressions, calculate subnets, decode JWTs and more.
Everything runs in your browser. Your input never leaves the page.
// Tools available in English
58 tools are available in English so far. Each one is free, needs no account, and keeps working offline once the page has loaded.
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.
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.
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.
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.
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.
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.
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.
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.
// Browse by category
Each category page explains what the tools in it are for and what tends to go wrong in that area.
// What these tools are for
Most of the work these tools do is work you could do another way, given time: read a cron field carefully, count subnet bits on paper, decode a token with a one-line script, look up whether a US gallon and an imperial gallon are the same thing. The reason to use a tool instead is not that the task is hard but that it interrupts something else, and that a plausible-looking wrong answer is easy to produce and expensive to discover later.
A cron expression that you read as "every five minutes" but that actually fires at five past the hour will not raise an error; it will simply run twelve times less often than you assumed. A directory left at 644 will refuse every attempt to enter it, because traversing a directory needs the execute bit rather than the read bit. A /26 offers 62 usable addresses, not 64, because the network and broadcast addresses cannot be assigned to a host. Each of these is obvious once stated and easy to get wrong at half past five on a Friday.
So each tool here shows its working: the calculator prints the symbolic permission string next to the octal
value and an ls -l style preview, the cron parser explains every field in words and lists the
next run times, the subnet calculator gives the full range rather than just a count. The aim is that you can
check the answer rather than take it on trust.
// Why everything runs in your browser
The input to a developer tool is frequently the input you least want to hand to a stranger. A JWT taken from
a failing request contains a user identifier and an expiry, and while it lasts it is a credential. A curl
command copied from a terminal usually carries an Authorization header. A configuration file
whose permissions you are checking often sits next to a private key. Many online tools for exactly these
jobs post the input to a backend, where at minimum it passes through logs.
Every tool on this site is implemented as client-side JavaScript. The page is static, the logic is already in the browser by the time you paste anything, and there is no endpoint to send data to. You can confirm this from the network tab of your browser developer tools: paste a token into the JWT decoder and watch that no request goes out. The practical consequence is that these tools remain usable with real material, and that they keep working when you are offline or on a restricted network.
Where a tool remembers something between visits — the unit category you last opened, the diagram you were drafting — it uses your browser local storage. That data stays on your machine, is not readable by this site, and can be cleared from your browser settings at any time. The privacy policy sets this out in full, including what the analytics and advertising scripts do collect.
// About Retro Web Tools
Retro Web Tools is a collection of free browser-based utilities for developers, sysadmins and designers, wrapped in a CRT-terminal look. The Japanese edition offers 59 tools; the English edition is being rolled out starting with the ones most often needed.
The retro presentation is deliberate but it is only presentation. Underneath, the pages are plain static HTML with no framework overhead on the parts that do not need it, which is why they load quickly and work on an old phone as readily as on a workstation.
// Frequently asked questions
- Are these tools really free?
- Yes. Every tool is free to use with no account, no trial period and no feature held back behind a paywall. The site is supported by advertising, which is why you will see ad slots on some pages.
- Is my data uploaded anywhere?
- No. Each tool is implemented as client-side JavaScript, so the text, tokens and files you work with are processed inside your own browser and never reach a server operated by this site. That is what makes it reasonable to paste a production access token into the JWT decoder or a real configuration file into the chmod calculator.
- Do I need to install anything?
- No. Open the page and start working. Once a tool page has loaded it will keep working without a network connection, because all of the logic is already in the browser.
- Why are there fewer tools in English than in Japanese?
- The site started in Japanese and currently has 59 tools there. The English edition began as a pilot with the 58 tools that were most often needed by an international audience, and is being extended based on what people actually search for. The tools themselves are identical; only the surrounding explanation differs.
- Can I use these tools at work, with company data?
- The processing model makes that practical: nothing you enter is transmitted, so there is no third party receiving your data. Your own organisation may still have policies about which websites may be used for which material, and those apply as they would to any other site.
- Which browsers are supported?
- Current versions of Chrome, Edge, Firefox and Safari, on desktop and mobile. A few tools rely on newer browser APIs, such as the clipboard and file APIs, and will tell you if something is unavailable.