LangChain.js

apiVersion: v1
runtime: node22
entrypoint: agent.ts#chain
dependencies: package.json

{
  "type": "module",
  "dependencies": {
    "@langchain/core": "^1.0.0",
    "@langchain/openai": "^1.0.0"
  }
}

import { ChatPromptTemplate } from '@langchain/core/prompts'
import { StringOutputParser } from '@langchain/core/output_parsers'
import { RunnableSequence } from '@langchain/core/runnables'
import { ChatOpenAI } from '@langchain/openai'

// Reads OPENAI_API_KEY, which you add as a secret on the agent's Config tab.
const prompt = ChatPromptTemplate.fromMessages([
  ['system', 'Summarise what the user says in one line.'],
  ['human', '{input}'],
])

// The prompt arrives as a string, so the first step shapes it for the template.
export const chain = RunnableSequence.from([
  (input: string) => ({ input }),
  prompt,
  new ChatOpenAI({ model: 'gpt-5' }),
  new StringOutputParser(),
])