Rantjs

Write a pattern. Get a sentence. A seeded procedural-text engine for JavaScript — names, verbs, places, and the glue between them — without a template language, a model call, or a bag of Math.random().

Live demo · Inspired by Rant. This is the Rantjs dialect (<noun>, [rep:3]{...}), not a Rant 4 VM.

import { rant } from "rantjs";

rant(
  "<firstname male> likes to <verb-transitive> <noun.plural> with <pron poss male> pet <noun-animal> on <timenoun dayofweek plural>.",
);
// 'Sean likes to chop parrots with his pet cat on Saturdays.'

npm install rantjs
npx rantjs --seed 42 '<firstname male> found [a] <noun-animal>.'

Why Rantjs

• One function. rant(pattern) returns a string. Compile the pattern when you will run it more than once.
• Repeatable. The same pattern plus the same seed is the same sentence. That makes tests, save games, and LLM pipelines honest.
• Characters stay themselves. Name a result once (<firstname male :: hero>) and reuse it (<::hero>) so the hero does not change gender mid-paragraph.
• A real dictionary. Compiled from Rantionary, indexed by class. Queries do not scan the whole noun table to find animals.
• A small language. Queries, weighted blocks, repeaters, articles, case, synchronizers. You describe the shape of the text; the dictionary fills it.
• Runs everywhere. ESM, CommonJS, CLI, and a minified browser IIFE. The Node build does not touch window. Import rantjs/engine if you want the interpreter without English.
• NSFW is a flag. Entries tagged nsfw stay out unless you pass { nsfw: true } or query that class. The shipped English dictionary has none.

Use it for NPC chatter, item flavor, test fixtures, prompt variation, worldbuilding, and any place a hardcoded string would go stale.

Give it to an LLM

Paste the block below into ChatGPT, Codex, Claude, or another coding assistant, then replace the bracketed brief. It is enough for the model to call rant() and write valid patterns.

Build [DESCRIBE THE FEATURE] using rantjs, a procedural text generator for JavaScript.

Install: npm install rantjs
Import: import { rant, compile, createRant, explain, enUS } from "rantjs";

API:
- rant(pattern, options?: { seed?: number | string, nsfw?: boolean, dictionary?: Dictionary }): string
- rant(pattern, customDictionary)
- compile(pattern, defaults?) -> { run(options?) }   // parse once, run many
- createRant(options) -> { run(pattern, options?), compile(pattern) }
  Unseeded run() calls on one instance share one RNG stream.
- explain(pattern, options?) -> { text, picks }      // which dictionary rows were chosen
- Engine only (no English dictionary): import { rant } from "rantjs/engine"
- .dic compiler: import { compileDic } from "rantjs/dic"

Rules:
- Do not concatenate random words yourself. Write a Rantjs pattern and call rant() or compile().
- Pass a seed when output must be repeatable (tests, saved content, screenshots).
- Do not invent dictionary tables. Use only the tables listed below.
- Filters and inflections go inside the query. Separators may be space, dash, or dot: <noun animal plural>, <noun-animal plural>, <verb.ed> are the same idea.
- Unknown tags throw. Do not use channels, subroutines, query builders, or replacers — those are gone in 3.0.
- this is NOT React. There is no component API in rantjs.

Pattern dialect:
- Query: <table filter inflection>
- Carrier (remember a value): <firstname male :: hero> … <::hero>
  Unique (no repeats in one run): <noun-animal ::!pet>
- Block (pick one): {heads|tails}     Weighted: {(80)common|(20)rare}
- Repeat next block: [rep:3]{x}       Join: [sep:\s] or [sep:\n] or [rs:3;.]
- Article: [a] next word becomes "a" or "an"
- Case for the finished string: [case:none|first|word|title|upper|lower|sentence]
- Integer: [n:min;max]     Format: [numfmt:verbal|roman|hex]
- Branch: [if:carrier]{then}{else}
- Chance the next block runs: [chance:50]{maybe}
- Lock two blocks to the same pick: [x:name;locked]{A|B}[x:name;locked]{A|B}
- Random A–Z letter: \C
- Nested braces are allowed. Unknown queries are left in the output; they do not print "undefined".

Dictionary tables (en-US):
abstract, activity, adj, adv, alien, amount, color, conj, country, em, emo,
face, faced, firstname (alias: name), greet, noun, place, prefix, prepos,
preposition (alias: with), pron (alias: pro), quality, rel, say, sconj,
sound, substance, surname, timeadv, timenoun, title, unit, verb, verbimg,
vocal, x, yn

Useful filters / inflections:
- firstname: male, female
- noun: plural (alias pl), animal, tool, surface, furniture, body, liquid,
  insect, clothes, plant, person, ball, fruit, container, job, weapon, food,
  vehicle, shape
- verb: transitive, intransitive, ed, ing, s
- pron: poss, male, female, acc, nom, self
- yn: yes, no
- timenoun: dayofweek, month, holiday, plural
- rel: male, female
- adj, adv, place, color, greet, title, country work as <table> with optional class filters

Custom dictionary shape if you must add words:
{
  tables: {
    pet: {
      name: "pet",
      subs: ["default", "plural"],
      entries: [{ forms: ["capybara", "capybaras"], classes: ["animal"] }],
    },
  },
}

Browser without a bundler:
<script type="module">
  import { rant } from "https://cdn.jsdelivr.net/npm/rantjs@3.0.0/+esm";
</script>
or
<script src="https://cdn.jsdelivr.net/npm/rantjs@3.0.0/dist/rant.min.js"></script>
<!-- IIFE assigns rant on globalThis. The Node/ESM build does not. -->

Return working code. Prefer one or two rich patterns over many tiny ones.

Patterns

Queries pull a random dictionary entry:

<firstname male>
<noun-animal plural>
<verb.ed>
<pron poss male>
<yn yes>

Blocks choose an alternative. A block with no repeater runs once. | splits options. Nested braces work. Prefix an option with (weight) to bias it.

{heads|tails}
{Example text}
[rep:3][sep:\s]{click|clack}
{(80)common|(20)rare}

Tags

Carriers remember a result so a character stays the same person:

<firstname male :: hero> saw <::hero> in the <place>.

Escapes: \C is a random A–Z letter.

Entries tagged nsfw are omitted unless the query asks (<noun nsfw>) or you pass { nsfw: true }. The shipped English dictionary does not include any.

Unknown tags throw. Unknown query tables are left in the output as <raw>.

API

import { rant, compile, createRant, explain, enUS } from "rantjs";

rant(pattern);
rant(pattern, { seed: 42 });
rant(pattern, { seed: "chapter-1", dictionary: enUS });

const line = compile(pattern);
line.run({ seed: 1 });
line.run({ seed: 2 });

const r = createRant({ seed: 42 });
r.run(pattern);
r.compile(pattern).run();

explain(pattern, { seed: 1 });
// { text, picks: [{ table, args, value, carrier }] }

Custom dictionary shape:

const pets = {
  tables: {
    pet: {
      name: "pet",
      subs: ["default", "plural"],
      entries: [{ forms: ["capybara", "capybaras"], classes: ["animal"] }],
    },
  },
};

Browser

ESM:

<script type="module">
  import { rant } from "https://cdn.jsdelivr.net/npm/rantjs@3.0.0/+esm";
  document.body.textContent = rant("<greet> <firstname>.");
</script>

Script tag (cdnjs / jsDelivr):

<script src="https://cdn.jsdelivr.net/npm/rantjs@3.0.0/dist/rant.min.js"></script>
<script>
  document.body.textContent = rant("<greet> <firstname>.");
</script>

The IIFE build assigns rant on globalThis. The Node/ESM build does not touch window.

CLI

rantjs '<pattern>'
rantjs --seed 7 -f story.rant
rantjs --nsfw '<adj nsfw> <noun>'

Development

npm install
npm test
npm run bench
npm run demo          # playground at http://localhost:5173

Dictionary sources live in vocab/ (Rantionary plus a few custom tables). npm run build:dict compiles them into src/dictionaries/en-US.ts.

The playground is a SvenJS 3.2.1 app (npm run demo). The live demo is at rantjs.vercel.app.

UI built with SvenJS 3.2.1.

Migrating from 2.x

• Node 20+.
• compile(pattern) and explain(pattern) are new. createRant().channels is gone.
• Unknown tags throw instead of no-oping.
• 1.x-shaped dictionaries ({ tokens, pet: { all: [...] } }) are no longer accepted. Pass { dictionary: { tables } }.
• Rhyme carriers (::&id), channels, subroutines, query builders, replacers, and targets are removed. Use match/unique carriers and JavaScript for the rest.
• Pronunciation strings are not in the shipped dictionary (they existed only for rhyme).
• { nsfw: true } still admits nsfw-class entries in your dictionary. The shipped English tables have none.
• parse, compileDic, and createRng are not root exports. Use rantjs/dic for the .dic compiler.
• import { rant } from "rantjs/engine" is the interpreter without English.

Migrating from 1.x

• Node 20+.
• import { rant } from "rantjs" (or require("rantjs").rant).
• window.rant is only set by the IIFE browser file, not by require("rantjs").
• String.prototype is no longer patched.

License

ISC