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Forty-two pieces of developer jargon you'll meet in a0a's tools. One short answer, one long answer, cross-references. Filter by category or use the browser's find-in-page. Nothing loads from the network.
Looking for how-tos instead of definitions? The concepts page covers workflows, principles, and pitfalls — when to reach for a tool, not just what a word means.
The 7-bit character set that covers English letters, digits, and common symbols. 128 codepoints total.
Every byte under 128 maps to one ASCII glyph. Almost every other text format — URLs, base64, UUIDs — is ASCII-safe by design, meaning the output contains only ASCII characters so it passes through systems that mangle non-ASCII bytes.
A way to encode any binary data as ASCII text using 64 printable characters.
Takes 3 bytes, produces 4 characters. Output is 33% larger than input. URL-safe base64 swaps '+' and '/' for '-' and '_' so the string can travel inside a URL without needing further escaping.
see also URL encoding · ASCII
A small signature computed from data, used to detect accidental changes.
Run the same data through the same algorithm, you get the same checksum. Change one bit, you get a different one. CRC32 and MD5 are fast-but-not-secure checksums; SHA-256 is cryptographic — same properties plus resistance to forgery.
Your OS's paste buffer. a0a reads from and writes to it with your permission.
Modern browsers require a click (not just a page load) before allowing clipboard writes. Reads are even more restricted — the browser asks your permission, and the answer is remembered per site. a0a never reads the clipboard; you paste explicitly.
A number assigned to a character in the Unicode standard.
Unicode has 1,114,112 codepoints. 'A' is U+0041. '€' is U+20AC. '🦀' is U+1F980. The codepoint is the identity of the character; the encoding (UTF-8, UTF-16) is how it gets stored in bytes.
The set of colors a model can express, defined by axes and primaries.
sRGB is the web default — every browser can show it. Display-P3 is wider (phones, modern monitors). OKLCH can reference either. When you convert a bright Display-P3 color to sRGB, you 'clip' — some saturated colors simply cannot be reproduced.
How distinguishable two colors are, on a 1:1 to 21:1 scale.
WCAG defines minimums: 4.5:1 for normal text, 3:1 for large text. The ratio compares relative luminance, not hue — two colors with identical hue but different lightness can pass; two colors with wildly different hues but similar lightness will fail.
A one-way function that maps any input to a fixed-size fingerprint.
Three properties: deterministic (same input → same output), pre-image resistant (can't derive input from output), collision resistant (can't easily find two inputs with the same output). SHA-256 is the workhorse; MD5 and SHA-1 are broken and should not be used for security.
Same input always produces the same output.
A hash is deterministic. A UUID v4 is not. A regex match is. Random bytes aren't. In tools, 'deterministic' usually means a result you can verify later by rerunning the same input — a powerful property for audits.
A method for generating strong passphrases by rolling physical dice.
Roll five dice, get a 5-digit number, look up the word in a published Diceware list of 7,776 words. Six words = ~77.5 bits of entropy. The words are pronounceable English, which makes them easier to memorise than a random character string.
see also Entropy
A measure of unpredictability. Usually quoted in bits.
One bit of entropy = one yes/no choice. A 4-digit PIN has ~13 bits. A 6-word Diceware phrase has ~77 bits. A 128-bit key has, well, 128 bits — enough that brute-forcing it is considered physically impossible.
see also Diceware
Seconds (or milliseconds) since 1970-01-01 00:00:00 UTC.
Also called Unix time. A single integer that uniquely identifies a moment. 1700000000 is Nov 14 2023. Developers prefer it because timezone arithmetic disappears: two epochs subtract cleanly into a duration.
see also UTC
A simple pattern language for matching filenames.
'*' matches any characters. '?' matches one character. '**' (when the tool supports it) matches any number of nested directories. Globs are not regular expressions — they're much simpler, and that's the point.
A smooth transition between two or more colors.
A gradient has stops (colors at specific positions) and an interpolation space (how intermediate colors are calculated). OKLCH interpolation produces smoother transitions than RGB because lightness stays visually uniform.
A fixed-size fingerprint computed from input of any size.
See Cryptographic hash. In programming, 'hash' often refers to any function from data to fixed size — including fast ones like CRC32 that have no security guarantees. Context matters.
see also Cryptographic hash · SHA-256
Base-16 notation using 0–9 and a–f. Two hex digits = one byte.
Hex is the standard way to write bytes by hand. 0xFF is 255. A 16-byte UUID is often shown as 32 hex chars. A SHA-256 hash is 64 hex chars. Lowercase is conventional.
A color model with Hue, Saturation, and Lightness axes.
Hue is 0–360° (red/green/blue/red). Saturation is 0–100% (grey to full). Lightness is 0–100% (black to white). HSL is intuitive but perceptually uneven — a bright yellow at L=50% looks much lighter than a dark blue at L=50%.
Applying twice has the same effect as applying once.
Setting a key to 5 is idempotent (still 5 after two sets). Incrementing is not (7 after two increments). Tool operations are generally idempotent — running URL-encode on an already-encoded string just produces the same output, unchanged.
A text format for structured data: objects, arrays, strings, numbers, booleans, null.
Invented for JavaScript, now used by every language. Strict syntax: double quotes on keys, no trailing commas, no comments. JSON5 and JSONC are loose variants that allow comments and trailing commas.
see also YAML
A signed token carrying claims, used for authentication.
Three parts separated by dots: header, payload, signature. All base64url-encoded. The signature proves the token wasn't tampered with, so servers can trust the payload without storing session state. The payload is NOT encrypted — anyone with the token can read it.
see also Base64
A naming convention: lowercase words joined by hyphens.
Example: 'user-profile-avatar'. The standard for URL slugs, CSS custom properties, and HTML attributes. Easy to read, doesn't get broken by word-wrap.
see also Slug
A regional and language setting that affects formatting.
'en-US' produces 1,234.56. 'de-DE' produces 1.234,56. 'ja-JP' might use '1234.56' without separators. Locales govern dates, numbers, currency, and sorting — but not text content itself.
Latin-like placeholder text used while designing layouts.
From a distorted Cicero passage. Used because the text looks like real content without distracting readers who speak English. The passage begins 'Lorem ipsum dolor sit amet…' and continues for centuries of apparently meaningful but nonsense Latin.
The perceived brightness of a color.
Relative luminance is the weighted sum of R, G, and B with green weighted most heavily (because human eyes are most sensitive to green). WCAG contrast ratios are built on relative luminance differences.
see also Contrast ratio
A plain-text format that renders as styled HTML.
'# heading', '**bold**', '[link](url)'. Designed by John Gruber and Aaron Swartz in 2004 to be readable as-is while also being a valid source for HTML. Many dialects: CommonMark, GitHub-Flavored, MDX.
A perceptually uniform color model: Lightness, Chroma, Hue.
Unlike HSL or RGB, OKLCH is designed so equal numeric differences produce equal visual differences. A gradient in OKLCH looks smooth; the same gradient in RGB has dead zones near the midpoint. Modern CSS supports OKLCH natively.
A coordinated set of colors — a design's full color inventory.
Typically includes a brand primary, a brand secondary, an accent, a set of grey shades, and semantic colors (success, warning, danger). A good palette has consistent lightness stops (e.g. 50/100/…/900/950) so it composes predictably across backgrounds and text.
see also Gradient
A sequence of words used instead of a password.
Longer, easier to memorise, and typically stronger than a password. A four-word diceware passphrase already exceeds most password strength requirements. Always prefer passphrases over passwords where the system allows it.
A pattern language for matching text.
'[a-z]+' matches one or more lowercase letters. '\d{3}-\d{4}' matches a three-digit-dash-four-digit pattern. Powerful but cryptic. A0a's regex tester lets you see matches highlighted as you type, which shortens the learning curve considerably.
The base color model for displays: Red, Green, Blue, each 0–255.
Additive: mixing equal full R, G, B produces white. Every display — phones, TVs, monitors — uses some form of RGB. CSS accepts '#FF0080' hex, 'rgb(255, 0, 128)' decimal, and 'rgb(100% 0% 50%)' percentage.
Random bytes mixed into a password before hashing.
Without a salt, two users with the same password produce the same hash. With a random per-user salt, identical passwords produce different hashes. Salts defeat rainbow tables — precomputed hash lookups. Always salt. Always use a per-record salt.
see also Hash
A cryptographic hash function producing a 256-bit (32-byte) output.
Part of the SHA-2 family designed by the NSA in 2001. Still considered secure as of 2026. Output is usually shown as 64 hex characters. Used in Bitcoin, TLS certificates, file integrity checks, and virtually every modern cryptographic system.
see also Cryptographic hash
The '#!' at the start of a script telling the OS which interpreter to run.
'#!/usr/bin/env python3' says 'run this file with Python 3'. Only the first two bytes ('#' and '!') are magic; the rest is the path. Shebangs only work on Unix-like systems; Windows ignores them and uses file associations instead.
A URL-safe version of a string, usually for a page path.
'Hello World' → 'hello-world'. Lowercase, kebab-case, ASCII-only, no spaces, no punctuation. Good slugs are short, descriptive, and stable — URLs that outlive revisions of the underlying content.
see also Kebab-case
A naming convention: lowercase words joined by underscores.
Example: 'user_profile_avatar'. Standard in Python, Ruby, and C APIs. Cannot appear inside URLs without percent-encoding, which is why kebab-case wins for web paths.
Time-based one-time password. The 6 digits your authenticator app shows.
An algorithm that derives a short code from a shared secret and the current 30-second window. Both the server and your phone compute the same code at the same time. Defined in RFC 6238.
Escaping characters in URLs so they travel cleanly.
Also called percent-encoding. Space becomes '%20'. '?' becomes '%3F'. Applies to anything in a URL that isn't alphanumeric or -._~. Essential for any URL that embeds user-provided data as a query parameter.
see also Base64
Coordinated Universal Time. The global reference timezone.
UTC has no daylight saving. Every other timezone is described as 'UTC ± hours'. Servers, databases, and logs should always store UTC; conversion to local time happens at presentation.
see also Epoch time
A variable-length encoding for Unicode text.
ASCII characters take one byte. European letters take two. CJK characters take three. Emoji take four. UTF-8 is backward-compatible with ASCII and has become the overwhelmingly dominant encoding on the web and in file formats.
see also Codepoint
A 128-bit universally unique identifier.
v1: timestamp + MAC. v4: fully random. v7: timestamp-prefixed random (newer, sortable, recommended for new systems). Represented as 32 hex chars with 4 dashes: 'xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx'. Collision probability is negligible in practice.
see also Hex
Web Content Accessibility Guidelines — the standard for accessibility.
WCAG 2.2 defines conformance levels A, AA, and AAA. AA is the common legal baseline (contrast, keyboard access, captions, etc). Contrast requirements are one of the most measurable WCAG rules — hence their prominence in a0a's contrast tool.
see also Contrast ratio
A text format for structured data, easier to read than JSON.
Significant indentation. No braces or commas. Supports comments. Used heavily in CI configs, Kubernetes manifests, and Docker Compose files. The trade-off: indentation bugs can silently change meaning.
see also JSON
No terms in that category.
