Developer Tools

Learn what HTML entities are, why they exist, the most common named entities, how numeric entities work for any Unicode character, and when modern UTF-8 pages don't need them — with a free HTML entities tool.

HTML entities were invented to survive character encoding translation before UTF-8 was universal. In today's UTF-8 world, é and é are identical — but five entities (&, <, >, ", ') remain essential because they escape characters that have structural meaning in HTML, not encoding meaning. Here's which entities are legacy, which remain necessary, and why   is a special case that's about rendering behavior rather than encoding.

Short-lived access tokens require a refresh mechanism — and how you implement that mechanism determines your app's security and user experience. Here's refresh token rotation, silent refresh in SPAs, theft detection via refresh token families, and the cases where server-side sessions are simpler and safer.

Y2K cost $300–600 billion to mitigate. The Unix 2038 problem will overflow signed 32-bit timestamps on 19 January 2038. Excel has counted 29 February 1900 as a real date since the 1980s. Here's the structural causes of each date bug and which ones are still ticking.

Most developers can convert hex to decimal — but two's complement, signed overflow, and bit-width boundaries are where base conversion becomes genuinely useful for debugging real problems.

Structured JSON logs are queryable across millions of events in milliseconds; unstructured string logs require brittle grep. Here's why JSON logging matters, the OpenTelemetry log schema standard, structured logging libraries in Python/Node/Go, and how formatting API error responses reveals everything needed to debug a production incident.

Hashing the same file twice, a year apart, on different computers, produces the exact same hash — this single property, determinism, is the foundation of file-integrity verification. Here's how the avalanche effect guarantees "match or no match, with no partial credit," why fixed output size makes hash comparison practical for huge files, the proper download-verification workflow, and why where a published hash comes from matters as much as the comparison itself.

Learn how to use a JWT decoder to debug 401 errors, understand the header, payload, and signature sections, check expiry and audience claims, and identify security issues like alg:none attacks.

Binary-Coded Decimal (BCD) encodes each decimal digit as a 4-bit group — which is why real-time clock chips return 0x59 to mean 59 seconds (not 89), and why hardware with BCD limits constrains values to 0-99 rather than 0-255. Here's BCD in RTC hardware and financial calculations, Gray code's one-bit-change property that prevents rotary encoder errors, and why TCP checksums use one's complement arithmetic.

A practical reference of the regex patterns developers actually need — email, URL, UUID, IP address, dates, semver, hex colours, slugs, and more — with edge cases and caveats for each.