capstring

CaPiTaLiZe StRiNgS!

A small, serious, zero-dependency library for turning text into any case, code convention, or ridiculous fun style. Unicode and emoji safe. Ships a CLI and TypeScript types.

Features

• Every style you need - case, code conventions, encodings, and Unicode art
• Zero dependencies - one 17 kB file, browser-safe
• Unicode aware - Élan Vital, crème-brûlée, emoji and flags survive every style
• Smart tokenizer - XMLHttpRequest becomes xml-http-request, hello_world becomes helloWorld
• Website, HTTP API, and docs - capstring.netlify.app: playground, Developer Docs, API Reference
• CLI - npx capstring kebab "Hello World"
• TypeScript types - autocomplete for every style name
• 100% test coverage

Try it online

capstring.netlify.app - type anything, see every style, click to copy.

Installation

npm install capstring

Quick Start

import capstring from 'capstring';

capstring('hello world', 'title');     // 'Hello World'
capstring('hello world', 'kebab');     // 'hello-world'
capstring('hello world', 'constant');  // 'HELLO_WORLD'
capstring('hello world', 'sponge');    // 'HeLlO WoRlD'
capstring('hello world', 'flip');      // 'plɹoʍ ollǝɥ'
capstring('hello world', 'hashtag');   // '#HelloWorld'

CLI

# no install, runs the latest version each time
npx capstring kebab "hello world"          # hello-world

# or install once and use it anywhere
npm install -g capstring
capstring kebab "hello world"              # hello-world

npx capstring kebab "Hello World"          # hello-world
echo "hello world" | npx capstring title   # Hello World
npx capstring --all "hello world"          # every style, one per line
npx capstring --list                       # style names
npx capstring --count "hello world"        # words: 2, chars: 11, chars (no spaces): 10, spaces: 1
npx capstring snake --json "Hello World"   # {"input":"Hello World","style":"snake","output":"hello_world"}

Exit code 2 means a usage error (unknown style or option, missing text).

All Styles

Every style applied to hello world. Full explanations with more examples are in the Developer Docs.

Case

| Style | hello world becomes | |-------|------------------------| | same | hello world | | none | (empty string) | | proper | hello world | | title | Hello World | | sentence | Hello world | | upper | HELLO WORLD | | lower | hello world | | swap | HELLO WORLD | | capitalize | Hello world | | lowerfirst | hello world |

Code

| Style | hello world becomes | |-------|------------------------| | camel | helloWorld | | pascal | HelloWorld | | snake | hello_world | | kebab | hello-world | | slug | hello-world | | constant | HELLO_WORLD | | python | HELLO_WORLD | | dot | hello.world | | path | hello/world | | train | Hello-World | | hashtag | #HelloWorld | | acronym | HW | | ada | Hello_World | | cobol | HELLO-WORLD | | initials | H.W. |

Fun

| Style | hello world becomes | |-------|------------------------| | reverse | dlrow olleh | | sponge | HeLlO WoRlD | | mock | hElLo wOrLd | | alternate | hElLo WoRlD | | crazy | HEllo WorlD | | random | (random case, different every call) | | clap | hello 👏 world | | piglatin | ellohay orldway | | spaced | h e l l o w o r l d | | squish | helloworld | | nato | Hotel Echo Lima Lima Oscar / Whiskey Oscar Romeo Lima Delta |

Encodings

| Style | hello world becomes | |-------|------------------------| | leet | h3110 w0r1d | | rot13 | uryyb jbeyq | | morse | .... . .-.. .-.. --- / .-- --- .-. .-.. -.. | | binary | 01101000 01100101 01101100 01101100 01101111 00100000 01110111 01101111 01110010 01101100 01100100 | | hex | 68 65 6c 6c 6f 20 77 6f 72 6c 64 | | base64 | aGVsbG8gd29ybGQ= |

Unicode Art

| Style | hello world becomes | |-------|------------------------| | flip | plɹoʍ ollǝɥ | | smallcaps | ʜᴇʟʟᴏ ᴡᴏʀʟᴅ | | bubble | ⓗⓔⓛⓛⓞ ⓦⓞⓡⓛⓓ | | wide | ｈｅｌｌｏ　ｗｏｒｌｄ | | strike | h̶e̶l̶l̶o̶ w̶o̶r̶l̶d̶ | | bold | 𝗵𝗲𝗹𝗹𝗼 𝘄𝗼𝗿𝗹𝗱 | | italic | 𝘩𝘦𝘭𝘭𝘰 𝘸𝘰𝘳𝘭𝘥 | | script | 𝓱𝓮𝓵𝓵𝓸 𝔀𝓸𝓻𝓵𝓭 |

All code styles share one tokenizer: words split on whitespace, _, -, ., /, punctuation, emoji, and camelCase boundaries (XMLHttpRequest → xml-http-request). Letters stay attached to digits (utf8). Apostrophes are dropped (don't → dont).

API

capstring(str, style = 'same', options?)

import capstring from 'capstring';

capstring('hello world', 'title');  // 'Hello World'
capstring('hello world');           // 'hello world' (default: same)
capstring('');                      // ''
capstring(123);                     // false (not a string)
capstring('hello world', 'nope');   // 'hello world' (unknown style returns input)

// Strict mode throws instead
capstring(123, 'title', { strict: true });    // TypeError
capstring('hi', 'nope', { strict: true });    // RangeError

capstringAll(str, options?)

Every style at once, keyed by style name in STYLES order.

import { capstringAll } from 'capstring';

const all = capstringAll('hello world');
all.kebab;   // 'hello-world'
all.morse;   // '.... . .-.. .-.. --- / .-- --- .-. .-.. -..'
all.nato;    // 'Hotel Echo Lima Lima Oscar / Whiskey Oscar Romeo Lima Delta'

getStyles(), isValidStyle(style), STYLES, CATEGORIES

import { getStyles, isValidStyle, STYLES, CATEGORIES } from 'capstring';

getStyles();              // ['same', 'none', 'proper', ...] (fresh copy)
isValidStyle('kebab');    // true
STYLES;                   // frozen array of every style name
CATEGORIES.art;           // ['flip', 'smallcaps', 'bubble', 'wide', 'strike'] (frozen)

TypeScript

import capstring, { type Style } from 'capstring';

const style: Style = 'kebab';   // autocompletes every style name
capstring('Hello', style);      // string

HTTP API

Free, no key, CORS enabled, hosted at https://capstring.netlify.app/api. Interactive reference with try-it-out: capstring.netlify.app/api.

curl https://capstring.netlify.app/api/title/hello%20world
# {"input":"hello world","style":"title","output":"Hello World"}

curl https://capstring.netlify.app/api/sponge/hello%20world.txt
# HeLlO WoRlD

curl -H "Accept: text/csv" https://capstring.netlify.app/api/all/hello%20world

curl -X POST https://capstring.netlify.app/api/batch \
  -H "Content-Type: application/json" \
  -d '{"style":"slug","texts":["hello world","Hello World"]}'

| Endpoint | Returns | |----------|---------| | GET /api/:style/:text | { input, style, output } | | GET /api/all/:text | every style | | POST /api/batch | { style, texts[] } (max 1,000 texts, 100,000 characters in total) | | GET /api/spell/:text | spell-corrected text plus a corrections list, optional ?style= | | GET /api/count/:text | words, characters, characters without spaces | | GET /api/lorem/:count | lorem ipsum words (1 to 1000), optional ?style= | | GET /api/badge/:style/:text | shields-style SVG badge, ?label= to override the left side | | GET /api/styles | style names and categories |

Output is JSON by default. Pick another format with an extension (.txt, .html, .xml, .yaml, .csv, .jsonp, .svg or .png for the result as an image), ?format=, or an Accept header. Text is limited to 10,000 characters (500 for spell); GET URLs are capped around 8 KB by the host, so use POST /api/batch for longer text. Errors come back in the same format as { "error": { "code", "message" } }.

Behavior notes

Exact rules for title, sentence, slug, the tokenizer, and Unicode handling are documented per style in the Developer Docs. The short version: every style iterates code points, the reordering and art styles iterate grapheme clusters, slug is ASCII only, and random is the only non-deterministic style.

Development

npm install            # Install dependencies
npm test               # Run tests
npm run lint           # Run linter
npm run test:coverage  # Test with coverage (100% required)
npm run dev            # Netlify Dev: site + API at http://localhost:8888

The website (web/: playground and Developer Docs; plain HTML/CSS/JS, no build step; the Swagger API Reference is served by the API function at /api) and the API (netlify/functions/api.js) both import index.js directly. The spellcheck and PNG dependencies (nspell, dictionary-en, @resvg/resvg-js) are devDependencies bundled into the function, with the fonts for PNG rendering vendored in netlify/fonts/, so the npm package itself stays zero-dependency.

Contributing

Please read CONTRIBUTING.md for details on the code of conduct and the process for submitting pull requests.

Versioning

This project uses Semantic Versioning 2.0.

Requirements

• Node.js 22.13+ (or any modern browser)
• ES modules (import/export)

License

MIT - Copyright 2016-2026 Brian Funk