Resources & Similar Tools

Specifications and standards

Primary sources. When documentation and a specification disagree, the specification wins.

• IETF RFC Editor — every internet standard, including RFC 3986 (URIs), RFC 4648 (Base64), RFC 8259 (JSON) and RFC 9110 (HTTP)
• WHATWG HTML Living Standard — the actual HTML specification browsers implement
• WHATWG URL Standard — the URL parsing algorithm as implemented, not as originally specified
• W3C Technical Reports — CSS, WCAG, SVG and the wider web platform
• The Unicode Standard — code points, encoding forms, normalisation and security annexes
• ECMAScript Language Specification — the normative definition of JavaScript
• NIST Special Publications — cryptographic standards and the SP 800-63 digital identity series
• Schema.org — the structured data vocabulary and its full type hierarchy

Documentation and learning

• MDN Web Docs — the best reference for JavaScript, CSS, HTML and browser APIs
• web.dev — Google's performance, Core Web Vitals and modern practice guidance
• Can I Use — browser support tables for every web platform feature
• Google Search Central — official documentation on crawling, indexing and rich results
• Bing Webmaster Guidelines — the other major search engine's documentation
• OWASP Cheat Sheet Series — concise, current security guidance by topic
• W3C Web Accessibility Initiative — WCAG, ARIA and practical accessibility techniques
• HTTP Archive — real-world data on page weight, technology adoption and performance

Other tools worth knowing

Tools built by other people that do things this site does not, or does differently. Listed because they are genuinely useful, not because of any arrangement.

Encoding and data

• CyberChef — chains dozens of encoding, encryption and analysis operations into a pipeline. Unmatched for multi-step transformations
• RapidTables converters — a very large set of numeric and unit conversion calculators
• JSON Formatter — JSON validation and formatting with a tree view
• CyberChef mirror — an alternative host for the same tool

Regular expressions

• regex101 — the reference regex debugger, with step-by-step match explanation across five flavours
• RegExr — a lighter interactive tester with a community pattern library

Web development

• W3C Markup Validation Service — checks HTML against the specification
• W3C CSS Validator — the equivalent for stylesheets
• PageSpeed Insights — lab and field Core Web Vitals data for any URL
• WebPageTest — deep performance analysis with waterfall charts and filmstrips
• WAVE — in-page accessibility evaluation from WebAIM
• axe DevTools — the accessibility engine most automated testing is built on

SEO

• Google Search Console — the only source of truth for how Google sees your site. Free
• Bing Webmaster Tools — the equivalent for Bing, with useful keyword data
• Rich Results Test — checks structured data eligibility
• Schema Markup Validator — general schema.org validation without the Google filter
• Screaming Frog SEO Spider — desktop crawler; free up to 500 URLs

Security

• Have I Been Pwned — checks whether an address appears in a known breach
• Qualys SSL Labs — detailed TLS configuration analysis
• Security Headers — grades your HTTP security header configuration
• Mozilla Observatory — broader security posture scanning

Books and long reads

• Joel Spolsky on Unicode — the 2003 essay that taught a generation why encoding matters
• Russ Cox: Implementing Regular Expressions — a four-part series on why backtracking engines are exponential
• Bit Twiddling Hacks — Sean Eron Anderson's catalogue of bit manipulation techniques
• Dan Luu — consistently rigorous writing on systems, performance and measurement
• Nand2Tetris — build a computer from logic gates upward; the best way to internalise binary

How this list is maintained

Everything here is included because it is used or has been used in the course of building this site. Links are checked periodically; if one has rotted or a recommendation no longer stands, please say so.

External links on this page carry rel="nofollow" as a matter of policy for outbound resource lists. That is not a judgement on the sites — several are better than anything here at what they do.