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