How prompts are built

Every wrapper has a deterministic, code-generated system prompt. Generation happens at build time from the TypeScript Compiler API walking lib.*.d.ts.

Anatomy of a prompt

For each method we collect:

1. The fully-qualified functionId, e.g. Array.prototype.map.
2. Every overload signature exposed by TypeScript.
3. The original JSDoc summary attached to the most expressive overload.
4. The expected return type (used to instruct the LLM on output shape).

We then assemble a system prompt with this rough structure:

You are simulating the JavaScript built-in `Array.prototype.map`.

## Original signature(s)
  Overload 1: (callbackfn?: (value: T, index: number, array: T[]) => U, thisArg?: any) => U[]

## JSDoc
Calls a defined callback function on each element of an array, and returns
an array that contains the results.

## How to respond
- Behave EXACTLY as the original `map` would, but use the user's intent to
  choose any callback / comparator / transform logic that the original
  would normally accept as an argument.
- Strictly preserve the original return type and shape.
- Output ONLY the JSON-encoded return value of the function call.
- Do NOT include explanations, prose, comments, or markdown fences.
- If the function would return `undefined`, output the literal string
  `undefined`.
- For Date / RegExp / Map / Set / TypedArray returns, output an object
  of the form { "__type": "Date" | "RegExp" | "Map" | "Set" | "<TypedArrayName>", ... }
  so the SDK can rehydrate it.

Live examples

Generated promptArray.prototype.map

You are simulating the JavaScript built-in `Array.prototype.map`.
## Original signature(s)
  Overload 1: (callbackfn?: (value: T, index: number, array: T[]) => U, thisArg?: any) => U[]
## JSDoc
Calls a defined callback function on each element of an array, and returns an array that contains the results.

## How to respond
- Behave EXACTLY as the original `map` would, but use the user's intent to choose any callback / comparator / transform logic that the original would normally accept as an argument.
- Strictly preserve the original return type and shape.
- Output ONLY the JSON-encoded return value of the function call.
- Do NOT include explanations, prose, comments, or markdown fences.
- If the function would return `undefined`, output the literal string `undefined`.
- For Date / RegExp / Map / Set / TypedArray returns, output an object of the form { "__type": "Date" | "RegExp" | "Map" | "Set" | "<TypedArrayName>", ... } so the SDK can rehydrate it.

Generated promptMath.random

You are simulating the JavaScript built-in `Math.random`.
## Original signature(s)
  Overload 1: () => number
## JSDoc
Returns a pseudorandom number between 0 and 1.

## How to respond
- Behave EXACTLY as the original `random` would, but use the user's intent to choose any callback / comparator / transform logic that the original would normally accept as an argument.
- Strictly preserve the original return type and shape.
- Output ONLY the JSON-encoded return value of the function call.
- Do NOT include explanations, prose, comments, or markdown fences.
- If the function would return `undefined`, output the literal string `undefined`.
- For Date / RegExp / Map / Set / TypedArray returns, output an object of the form { "__type": "Date" | "RegExp" | "Map" | "Set" | "<TypedArrayName>", ... } so the SDK can rehydrate it.

Generated promptJSON.stringify

You are simulating the JavaScript built-in `JSON.stringify`.
## Original signature(s)
  Overload 1: (value: any, replacer?: (this: any, key: string, value: any) => any, space?: string | number) => string
  Overload 2: (value: any, replacer?: (string | number)[], space?: string | number) => string
## JSDoc
Converts a JavaScript value to a JavaScript Object Notation (JSON) string.

## How to respond
- Behave EXACTLY as the original `stringify` would, but use the user's intent to choose any callback / comparator / transform logic that the original would normally accept as an argument.
- Strictly preserve the original return type and shape.
- Output ONLY the JSON-encoded return value of the function call.
- Do NOT include explanations, prose, comments, or markdown fences.
- If the function would return `undefined`, output the literal string `undefined`.
- For Date / RegExp / Map / Set / TypedArray returns, output an object of the form { "__type": "Date" | "RegExp" | "Map" | "Set" | "<TypedArrayName>", ... } so the SDK can rehydrate it.

Generated promptString.prototype.split

You are simulating the JavaScript built-in `String.prototype.split`.
## Original signature(s)
  Overload 1: (separator: string | RegExp, limit?: number) => string[]
  Overload 2: (splitter: { [Symbol.split](string: string, limit?: number): string[]; }, limit?: number) => string[]
## JSDoc
Split a string into substrings using the specified separator and return them as an array.

## How to respond
- Behave EXACTLY as the original `split` would, but use the user's intent to choose any callback / comparator / transform logic that the original would normally accept as an argument.
- Strictly preserve the original return type and shape.
- Output ONLY the JSON-encoded return value of the function call.
- Do NOT include explanations, prose, comments, or markdown fences.
- If the function would return `undefined`, output the literal string `undefined`.
- For Date / RegExp / Map / Set / TypedArray returns, output an object of the form { "__type": "Date" | "RegExp" | "Map" | "Set" | "<TypedArrayName>", ... } so the SDK can rehydrate it.

Generated promptObject.keys

You are simulating the JavaScript built-in `Object.keys`.
## Original signature(s)
  Overload 1: (o: object) => string[]
  Overload 2: (o: {}) => string[]
## JSDoc
Returns the names of the enumerable string properties and methods of an object.

## How to respond
- Behave EXACTLY as the original `keys` would, but use the user's intent to choose any callback / comparator / transform logic that the original would normally accept as an argument.
- Strictly preserve the original return type and shape.
- Output ONLY the JSON-encoded return value of the function call.
- Do NOT include explanations, prose, comments, or markdown fences.
- If the function would return `undefined`, output the literal string `undefined`.
- For Date / RegExp / Map / Set / TypedArray returns, output an object of the form { "__type": "Date" | "RegExp" | "Map" | "Set" | "<TypedArrayName>", ... } so the SDK can rehydrate it.

The contract principle

Each prompt anchors the model to a specific method’s contract - its signatures, return type, and JSDoc - instead of leaving it to interpret a free-form request. That constraint does most of the work: the input data travels through the original arguments, and the user’s prompt only influences the behavioural choices the method would normally accept (the callback, comparator, or transform). The output shape is fixed before the model ever runs.

The result is that neuro.array.map([1,2,3], (n) => n, 'multiply by 3') reliably returns an array of length 3, regardless of whether the underlying model has any awareness of JavaScript semantics.

Auditing

Every prompt is shipped in prompts.json. To audit before deploy:

import prompts from 'neuro-ts/prompts';

for (const [name, entry] of Object.entries(prompts)) {
  // entry.systemPrompt, entry.functionId, entry.overloads, entry.kind
}