Free Online Developer Tools for Web & Sysadmins
A focused toolkit of fast, privacy-first utilities for engineers: HTTP headers, JWT tokens, regex, subnets, MIME types, Base64 and accessibility contrast. Every calculation runs 100% locally — your data never leaves your device.
✓ No Login Required
Open a tool and use it instantly — no account, no sign-up form.
✓ 100% Local Processing
Every calculation runs in your browser. Your data never leaves your device.
✓ Free Forever
All core tools are free to use with no limits and no paywalls.
✓ No Data Tracking
No cookies for tracking, no uploads, no storage of your input.
Developer Tools
Vertical, engineering-focused utilities — not a junkyard of generic converters. Each tool has its own page with documentation and FAQ, and works offline once loaded.
HTTP Header Analyzer
Parse, analyze and compare raw HTTP request/response headers. Detect CORS, caching and security header issues.
Open tool→JWT Parser & Validator
Decode JWT tokens, validate exp/nbf timestamps and verify HS256/HS384/HS512 signatures locally — your secret never leaves the browser.
Open tool→Regex Explainer & Tester
Test regular expressions live with match highlighting, and get a plain-English explanation of every piece of your pattern.
Open tool→CIDR & Subnet Calculator
Calculate network address, broadcast, subnet mask, usable host range and host count from any IPv4 CIDR block.
Open tool→MIME Type Lookup
Look up MIME types from file extensions and vice versa, with ready-to-copy nginx and Apache config snippets.
Open tool→Base64 Batch Encoder / Decoder
Encode or decode multiple lines of text to and from Base64 in one batch — with UTF-8 support and invalid-input detection.
Open tool→WCAG Color Contrast Checker
Check text-to-background contrast ratios against WCAG AA and AAA standards, with pass/fail results for normal and large text.
Open tool→Latest from the blog
Deep dives on web security, networking and accessibility.
What Is a JWT Token and How Does It Work?
A plain-English guide to JSON Web Tokens: how JWTs are structured (header, payload, signature), how signature verification works, common claims like exp and nbf, and when not to use JWTs.
August 20, 2026 · 7 min read
Web SecurityHTTP Security Headers Explained: A Practical Guide for Developers
What every web developer should know about HTTP security response headers: HSTS, Content-Security-Policy, X-Frame-Options, X-Content-Type-Options, Referrer-Policy and more — with recommended values.
August 28, 2026 · 8 min read
NetworkingUnderstanding CIDR and Subnet Masks: A Developer-Friendly Guide
Learn how CIDR notation works, how prefix lengths map to subnet masks and host counts, what network and broadcast addresses are, and how to subnet for cloud VPCs, Kubernetes and firewalls.
September 1, 2026 · 8 min read
AccessibilityWeb Accessibility: A Practical Guide to WCAG Color Contrast
How WCAG contrast ratios work, the AA and AAA thresholds for text and UI elements, why low contrast excludes users, and a workflow for designing and fixing accessible color pairs.
September 5, 2026 · 7 min read
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No accounts, no cookies for tracking, no server-side processing of your input. Pages are static and load instantly — and every tool page includes plain-English documentation, so what you learn here you can take anywhere.
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