Converters, Formatters & Checkers

Formats JavaScript, HTML and CSS and unpacks minified code. Against Prettier it needs no install and can open obfuscated output back up — which is what you want when inspecting someone else’s minified bundle.

A collection of formatting, validation and conversion tools covering JSON, XML, YAML, SQL and Base64. Against IT Tools it is broader but heavier on ads — it is hard to find a conversion it lacks.

Tests an API’s CORS headers from the outside. Unlike the vague CORS error in the browser console, it tells you plainly which header is at fault.

Translates a cron expression into plain language as you type and shows the next run times. Unlike reading the man page you see the result instantly — the end of guesswork over asterisks and slashes.

GCHQ's in-browser data transformation tool: base64, hex, crypto, compression and parsing chained as a drag-and-drop 'recipe'. Unlike single-purpose encoders it chains hundreds of operations, and the page can be saved to run offline.

A visual regex tester that draws the expression as a state diagram, covering JavaScript, Python and PCRE. Where regex101 lists tokens, this draws a flow chart, which reads better for nested groups.

A diff tool for text, images, PDFs and folders. Against the diff command it handles formatted and visual comparison — the command line will not tell you what changed between two PDF contracts.

Paste a shell command and it maps every fragment to its entry in the man page. Against reading man it works backwards — you learn what the -xzvf in front of you means without scanning the manual.

A collection of developer tools: a REST client, a SQLite browser, XML and JSON validators, regex testing. Against collections like IT Tools it runs the heavier things — a database browser and an API client — in the browser too.

A tool generating realistic fake test data to a given schema (CSV, JSON, SQL). Unlike making data up by hand it produces fields like names and addresses consistently and in bulk.

A browser tool for drawing points, lines and polygons on a map while editing the GeoJSON in a side panel; it exports to KML, shapefile, CSV and other formats. Unlike QGIS it needs no install: it is for quickly drawing or fixing a small piece of data, not for analysis.

Generates a .gitignore from your operating system, editor and language choices. Unlike GitHub’s individual templates, it merges several at once — the end of retyping the same lines on every project.

Checks whether a site is flagged as unsafe in Google’s Safe Browsing records. Unlike multi-engine scanners such as VirusTotal it consults only Google’s list — so you see in advance the warning Chrome users would get.

A two-way converter between decimal and IEEE-754 floating point, with individual bits toggleable. Against a calculator it shows where the rounding error comes from — this is where the 0.1 + 0.2 question is actually answered.

A Portuguese-language site bundling small text utilities — reversing, counting, converting and more. Unlike single-purpose sites, it gathers dozens of small tools at one address.

Eighty-odd developer utilities on one page: hashes, JWT decoding, cron expressions, UUIDs, colour conversion. Unlike the one-tool-per-site alternatives, everything runs in the browser and the whole thing self-hosts with Docker, so nothing leaves your machine.

A tool that minifies JavaScript in the browser to shrink its size. Unlike build-pipeline tools such as Terser or esbuild, it handles a one-off job with nothing to install.

Draws JSON as a node graph rather than a tree, so nested structures are visible at a glance. Against a JSON formatter that graph view is the point — faster than counting indentation to work out the shape of a deep response.

A browser tool to inspect and edit JSON in tree and text views. Unlike a plain editor it folds and validates the structure, making large JSON easy to navigate.

A simple tool that alphabetically sorts and formats JSON keys. Unlike command-line tools such as jq it works in the browser with no query to write — handy for sorting two JSON files before comparing them.

A JSON validator and formatter that tells you which line failed and why. Against an editor plugin it needs nothing installed, which is what you want when checking a malformed API response in a hurry.

Bundles network tools like ping, traceroute, HTTP header and performance tests. Unlike pinging from your own machine, it runs the tests from servers in different parts of the world.

A collection of developer converters, formatters and generators. Against compilations like IT Tools it keeps visual and textual tools together — colour, image and code utilities in one place.

The classic generator of placeholder text (lorem ipsum) for design mockups. It stands in temporarily instead of real content, and the page also explains where the text comes from.

A browser tool that simplifies map data in shapefile, GeoJSON, TopoJSON or CSV and converts between those formats; the same operations can be scripted with its command-line version. Unlike geojson.io it is not for drawing but for shrinking large boundary files for the web.

Generates realistic fake test data (CSV, JSON, SQL) to your chosen schema. Unlike libraries such as Faker, you define fields in a UI without code and download thousands of rows.

A simple password generator with adjustable length and character sets. Unlike online generators that call a server it is a static page — the password is generated in your browser.

Explains an expression token by token, and its debugger shows exactly where a match breaks down. Unlike RegExr, you can switch between the PCRE, JavaScript, Python and Go flavours.

Turns a JavaScript regular expression into a railroad diagram, with groups, alternatives and repetition drawn as boxes and arrows. Unlike regex101 it does not test matches: it is for grasping the structure of someone else’s complex expression at a glance.

A regex tester and an alternative to regex101, with a simpler interface and a community library of patterns.

Draws JavaScript regular expressions as railroad diagrams. Against Debuggex it runs entirely client-side and exports the diagram as SVG, which makes it useful for documentation.

A collection of online debugging and network tools for developers and sysadmins. Unlike single-purpose tool sites, it gathers DNS, HTTP and encoding tools in one place.

A form that generates the CAA DNS record, which controls which certificate authorities may issue certificates for your domain, by picking authorities from a list. Instead of hand-writing the syntax it gives the lines to paste into your DNS provider.

You build a table cell by cell in a visual grid and it emits LaTeX, HTML, Markdown, plain text or MediaWiki, and accepts pasted CSV. Unlike writing a tabular by hand it generates the merged-cell and border code for you.

Strips a page to text only. Unlike a browser’s reader mode it converts the whole page to plain text — besides removing ads and layout noise, it roughly approximates what a screen reader sees.

A collection of format converters — JSON to TypeScript types, HTML to JSX, SVG to a React component. Instead of hunting a separate site for each conversion, they are all in one place.

A tool and browser extension revealing which technologies (framework, server, analytics) a website runs on. Unlike reading the source by hand, it recognises the fingerprints automatically.

HubSpot’s free tool grading a site on performance, SEO, mobile and security. Compared with Lighthouse it is shallower, but turns the result into a report card a non-technical person can follow.

Crawls a site and builds the sitemap.xml file for search engines. Unlike a site generator’s built-in sitemap it can crawl any site from outside; the free version is capped at 500 pages.