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Practical developer references, organized by topic.
Encodings
How text and binary become bytes: Base64, URL encoding, UTF-8.
Base64 encoding
What Base64 is, why it exists, how it works, and the cases where it is the wrong tool.
URL encoding (percent-encoding)
Why spaces and symbols in a URL get turned into %20 and friends, and the difference between query and path encoding.
UTF-8 and character sets
Why 'one character = one byte' is wrong, what code points are, and how UTF-8 became the default for the web.
Hashing & checksums
Fingerprints for integrity and passwords: MD5, SHA-1, SHA-256.
Hash functions: MD5, SHA-1, SHA-256
What a cryptographic hash is, how the common algorithms differ, and why MD5/SHA-1 are retired for security.
Checksums & verifying files
How to confirm a downloaded file is intact and unmodified using a checksum, and the limits of the technique.
Data formats
JSON and CSV: shape, rules, and safe conversion.
JSON basics
The shape of JSON, how it maps to language types, and the easy mistakes that produce invalid JSON.
CSV vs JSON
When a flat table beats nested documents, and how to convert between them safely.
Dates & time
Timestamps, UTC, and why time zones are harder than they look.
Unix timestamps & UTC
Why storing time as a single number avoids almost every timezone bug, and the 2038 problem you should know about.
Time zones & UTC offsets
Why 'UTC+8' lies, what IANA zone names are for, and how to avoid the classic off-by-one date bugs.
Regular expressions
The daily regex constructs, with runnable examples.