interface SynthesisRequest {
description: string;
exampleInput?: string;
exampleOutput?: string;
}
export interface GeneratedTool {
name: string;
description: string;
inputSchema: Record<string, unknown>;
handlerCode: string;
}
const SYSTEM_PROMPT = `You are a tool generator. Given a description of a capability,
you produce a complete tool definition.
You MUST respond with valid JSON containing exactly these fields:
{
"name": "snake_case_tool_name",
"description": "Clear one-line description of what the tool does",
"inputSchema": {
"type": "object",
"properties": {
"param_name": { "type": "string|number|boolean|array|object", "description": "..." }
},
"required": ["param_name"]
},
"handlerCode": "... JavaScript function body ..."
}
IMPORTANT: handlerCode must be a regular string, NOT a template literal. Use regular quotes " and escape any quotes inside with \\". Do NOT use backticks.
Rules for handlerCode:
- It receives a 'params' object matching the inputSchema
- It must be a self-contained function body (no imports, no require)
- It has access to: Math, Date, JSON, Array, Object, String, Number, RegExp, Map, Set
- It does NOT have access to: fs, http, fetch, process, eval, Function constructor
- It must return a value (object, string, number, array)
- Keep it focused and under 100 lines
Example — for "Calculate body mass index":
{"name":"bmi_calculator","description":"Calculate BMI from weight (kg) and height (m)","inputSchema":{"type":"object","properties":{"weight_kg":{"type":"number","description":"Weight in kilograms"},"height_m":{"type":"number","description":"Height in meters"}},"required":["weight_kg","height_m"]},"handlerCode":"var bmi = params.weight_kg / (params.height_m * params.height_m); var category = bmi < 18.5 ? 'underweight' : bmi < 25 ? 'normal' : bmi < 30 ? 'overweight' : 'obese'; return { bmi: Math.round(bmi * 10) / 10, category: category };"}`;
export class Synthesizer {
private apiKey: string;
private model: string;
constructor(apiKey: string, model: string) {
this.apiKey = apiKey;
this.model = model;
}
async generate(request: SynthesisRequest): Promise<GeneratedTool> {
let userPrompt = `Generate a tool for: ${request.description}`;
if (request.exampleInput) userPrompt += `\n\nExample input: ${request.exampleInput}`;
if (request.exampleOutput) userPrompt += `\nExpected output format: ${request.exampleOutput}`;
const response = await fetch("https://openrouter.ai/api/v1/chat/completions", {
method: "POST",
headers: {
"Content-Type": "application/json",
"Authorization": `Bearer ${this.apiKey}`,
"HTTP-Referer": "https://github.com/EyeSeeThru/jit-tool-synthesis",
"X-Title": "JIT Tool Synthesis",
},
body: JSON.stringify({
model: this.model,
max_tokens: 2048,
messages: [
{ role: "system", content: SYSTEM_PROMPT },
{ role: "user", content: userPrompt },
],
}),
});
if (!response.ok) {
const error = await response.text();
throw new Error(`OpenRouter API error: ${response.status} - ${error}`);
}
const data = await response.json() as any;
const text = data.choices[0]?.message?.content || "";
// Try to extract JSON from response
let jsonStr = text.trim();
// Remove markdown code fences
jsonStr = jsonStr.replace(/^```json\s*/g, "").replace(/^```\s*/g, "").replace(/```$/g, "");
// Try to find JSON object
const firstBrace = jsonStr.indexOf("{");
const lastBrace = jsonStr.lastIndexOf("}");
if (firstBrace === -1 || lastBrace === -1) {
throw new Error("Synthesizer did not return valid JSON");
}
jsonStr = jsonStr.substring(firstBrace, lastBrace + 1);
const tool = JSON.parse(jsonStr) as GeneratedTool;
if (!tool.name || !tool.description || !tool.inputSchema || !tool.handlerCode) {
throw new Error("Generated tool is missing required fields");
}
return tool;
}
}
