🔧 Developer Tools
JSON, Base64, regex, and coding utilities — 50 free tools available. No signup required.
Formatters, encoders, decoders, generators and network lookups — the utilities you reach for mid-task and want to finish in five seconds without creating an account.
Everything that can run locally does. JSON, Base64, JWT, hashing, regex, diffing, CSV and SQL formatting all execute in your browser, which matters more than convenience: pasting a production JWT, an API response or a config file into a server-side tool means handing that data to someone else. These do not have a server to send it to.
The exceptions are the lookups that genuinely require a network — DNS records, SSL connectivity, MAC vendor resolution — and each of those pages states exactly what it queries and what it cannot determine.
Where to start
- JSON Formatter & Validator — Format, validate and minify, with the parse error located rather than just reported.
- JWT Token Decoder & Inspector — Decodes header and payload locally — the token never leaves your browser, which matters for a real one.
- Regex Tester — Live matching with capture groups, so you can see what a pattern actually captures.
- Diff Checker & Text Compare — Line-by-line comparison without uploading either file anywhere.
- Cron Expression Generator — Builds an expression and translates it back to English, which catches the classic day-of-week mistakes.
- DNS Record & Nameserver Inspector — Live A, AAAA, MX, TXT, NS and CNAME records with TTLs, which reveal caching behavior.
All developer tools (50)
JSON Formatter & Validator
Format and validate JSON in your browser, nothing uploaded. Covers the six value types, why trailing commas fail…
Base64 Encoder & Decoder
A Base64 encoder decoder for text, covering the URL-safe alphabet, padding and the 33% size overhead — and why…
URL Encoder & Decoder
A URL encoder decoder with a full percent-encoding reference and the encodeURI vs encodeURIComponent difference…
Regex Tester
Test regular expressions live against the JavaScript engine, with a flavor comparison for Python, Java, .NET and…
IP Address Lookup
Look up any IP address to find its geolocation, ISP, timezone, and more. Free IP lookup tool powered by ipapi.co.
Password Generator
A password generator with a passphrase mode: six random words is 77.5 bits, the same as a 12-character password.
Diff Checker & Text Compare
Compare two texts side by side in your browser, nothing uploaded. Explains unified diff format and why CRLF line…
CSV to JSON Converter
Convert CSV to JSON in your browser, with control over type inference so leading zeros survive.
Markdown Live Previewer
Write and preview GitHub-flavored markdown in real time. Features instant split-screen HTML rendering, code syntax…
HEX to RGB Color Converter
A HEX to RGB converter that also gives RGBA, HSL and CMYK, with a live picker, contrast check, and the 8-digit hex…
HTML to Markdown Converter
Convert HTML code snippets, articles, and rich text to clean GitHub-flavored markdown with code fences, headers…
Cryptographic Hash Generator
Generate secure cryptographic checksums and hashes (SHA-256, SHA-512, SHA-384, SHA-1) directly in your browser…
JWT Token Decoder & Inspector
A JWT decoder that also verifies the signature in your browser: HS256 with a secret, RS256 and ES256 with a public…
Cron Expression Generator
A cron generator with plain-English output, common recipes, and the field-count differences for Quartz, Spring and…
SQL Formatter & Beautifier
Format SQL for readable diffs and code review, with an identifier-quoting table for PostgreSQL, MySQL, T-SQL…
UUID / GUID v4 Generator
A UUID generator for bulk, cryptographically secure Version 4 UUIDs and GUIDs, with uppercase and hyphen-removal…
Unix Epoch Timestamp Converter
Convert Unix epoch timestamps (seconds & milliseconds) to human-readable UTC and local dates, or convert any date…
HTML Entity Encoder / Decoder
Encode and decode HTML entities with a full reference table, plus why entity encoding alone is not safe inside…
cURL Command to Code Converter
A curl converter that turns a pasted command into Fetch, Axios and Python requests code, parsed in your browser…
CSS Box Shadow Generator
A CSS shadow generator with sliders for offset, blur, spread and color, plus layering, inset, live preview and…
CSS Gradient Generator
Create vibrant CSS linear and radial gradients with custom color stops, angles, designer presets, and 1-click CSS…
SEO URL Slug Generator
Turn any title into a clean lowercase URL slug. Covers accent stripping limits, why hyphens beat underscores, and…
DNS Record & Nameserver Inspector
Inspect live DNS records, mail exchangers (MX), SPF/TXT records, and nameservers for any domain using Cloudflare…
HTTP Status Code Explainer
HTTP status code lookup for every standard response code — 200, 301, 404, 500, 502, 503 — in plain English, with…
User Agent & Browser Inspector
A user agent analyzer for your own browser string: operating system, browser engine, version, screen resolution…
IP Subnet Mask & CIDR Calculator
A subnet mask calculator for IPv4: CIDR prefix, network and broadcast address, usable host range, wildcard mask…
SSL / TLS Certificate & Security Inspector
An SSL certificate checker with an honest limit: a browser can prove the handshake succeeded, not read the…
TCP / UDP Port Database Reference
Search common TCP/UDP network ports (22, 80, 443, 3306, 5432, 8080) with protocol definitions, standard service…
JSON to XML & XML to JSON Converter
A JSON to XML converter that runs both directions and re-parses its own output before showing it, so what you copy…
JSON to YAML & YAML to JSON Converter
A JSON to YAML converter that runs both ways in your browser, covering implicit typing: why 1.20 becomes 1.2 and…
MAC Address & OUI Vendor Lookup
MAC address lookup against the IEEE OUI registry: identify the manufacturer — Apple, Cisco, Intel, Samsung…
HTML, CSS & JSON Code Minifier & Formatter
Minify and beautify HTML, CSS, and JSON code client-side. Reduce file payload size, strip whitespace, and improve…
Interactive Regex Builder & Tester
Test and debug regular expressions in real-time with group capture inspection, flag switches (g, i, m), and…
JSON API Mock Test Data Generator
Generate realistic mock JSON data arrays for frontend testing and prototyping.
Linux Chmod Permissions Calculator
Calculate Linux/Unix file permissions with interactive read, write, and execute checkboxes.
Markdown Table Generator & Spreadsheet
Create and format Markdown tables using a visual spreadsheet editor. Add rows, columns, adjust text alignment…
WCAG 2.2 Color Contrast Ratio Calculator
A color contrast checker for text and background: the WCAG 2.2 ratio with AA and AAA pass/fail for normal and…
RFC 4648 Base32 Encoder & Decoder
Encode text to Base32 or decode Base32 strings into plain text using standard RFC 4648 alphabet.
JWT (JSON Web Token) Builder & Simulator
A JWT builder that signs for real with Web Crypto HMAC-SHA256, plus decode and verify.
Security HTTP Response Header Generator
Generate HSTS, Content-Security-Policy, X-Frame-Options, Referrer-Policy and Permissions-Policy response headers…
Social Open Graph & Twitter Card Generator
An Open Graph generator for og: and Twitter Card meta tags, with a live preview of how the link renders on…
SEO Robots.txt & Sitemap Directives Generator
A robots.txt generator with correct Allow/Disallow precedence — and why Disallow blocks crawling but does not stop…
Binary, Decimal & Hex Converter
A binary decimal hex converter (and octal) with arbitrary precision, so 64-bit values stay exact.
Music BPM to Delay Milliseconds & LFO Rate Calculator
Calculate audio delay time in milliseconds (ms), reverb pre-delay, and LFO frequency in Hz for whole, half…
Favicon Generator
Make a favicon from an image, letters or an emoji. A genuine multi-image .ico, the small modern icon set, and four…
Canonical URL Generator
A canonical URL generator that strips tracking parameters, normalizes protocol/www/trailing-slash, and outputs a…
Email Deliverability Checker
An email deliverability checker that looks up a domain's real SPF and DMARC DNS records, and checks common DKIM…
Meta Tag Generator
A meta tag generator that produces title, description, robots, Open Graph, and Twitter Card tags from one form…
CSS Specificity Calculator
A CSS specificity calculator that breaks any selector into its (ID, class, element) score and compares two…
XML Sitemap Generator
An XML sitemap generator that turns a pasted list of URLs into a valid sitemap.xml with lastmod, changefreq, and…
Base64 is encoding, not encryption
This is the single most consequential misunderstanding in this category. Base64 converts binary data into a restricted character set so it can travel through systems that expect text. It is fully reversible by anyone, requires no key, and provides no confidentiality whatsoever. A credential stored Base64-encoded is a credential stored in plain text with an extra step. The same applies to a JWT: the header and payload are Base64url-encoded, not encrypted, and anyone holding the token can read every claim in it. The signature proves the token was not altered — it does not hide the contents.
Hashing and encryption solve different problems
A hash is one-way: it produces a fixed-length digest that cannot be reversed to recover the input. That is what makes it right for integrity checking and wrong for anything you need to read back. It also means MD5 and SHA-1, both available here, should be treated as checksums for detecting accidental corruption rather than as security primitives — practical collision attacks exist against both. For anything security-relevant, SHA-256 is the floor, and for password storage neither a plain hash nor a salted fast hash is appropriate; that needs a deliberately slow function such as bcrypt or Argon2.
What a browser cannot tell you about a network
Several tools in this category are limited by what a web page is permitted to observe, and each says so rather than filling the gap with plausible output. A browser cannot read a remote server's TLS certificate — no API exposes it — so our SSL tool reports whether a handshake completes and defers issuer, expiry and protocol detail to a server-side scanner. A MAC address carries no location information, so a vendor lookup returns a registrant and nothing more. Being explicit about the boundary is more useful than a confident answer that was never measured.
Regex: greedy, lazy, and the escaping that bites
Two patterns account for most regex frustration. Quantifiers are greedy by default, so `.*` consumes as much as it can and backtracks — matching from the first opening tag to the last closing one rather than the nearest. Appending `?` makes it lazy and usually fixes it. The second is character class escaping: a dot inside `[]` is a literal dot and needs no escape, while outside it matches anything. Testing against real input rather than reasoning about the pattern is faster than either, which is what the tester is for.
Frequently asked questions
Is my data uploaded when I use these tools?
Not for the local ones, which is most of them. JSON, Base64, JWT, hashing, regex, diff, CSV and SQL tools all run in your browser. The network lookups — DNS, SSL, MAC vendor — necessarily make a request, and each of those pages says what it sends.
Is it safe to paste a real JWT or API key here?
The JWT decoder and hash generator run entirely client-side, so nothing is transmitted. That said, treat any credential pasted into any browser tab as exposed to extensions and to anyone with access to your machine, and rotate anything you would not want logged.
Why does the SSL checker not show the certificate?
Because no browser API gives a web page access to a remote server's certificate. That requires a server-side connection. The tool reports what a browser genuinely establishes — whether the handshake completes — and links to scanners that can read the rest.
Are there rate limits?
The local tools have none. The ones backed by public APIs inherit whatever limits those services impose, and will tell you when a limit has been reached rather than showing an empty result.
Can I use these tools offline?
The client-side ones will keep working once the page has loaded, since the logic ships with the page. Anything that queries a live service needs a connection.