LangChain Adapter

The LangChain adapter provides unified access to multiple LLM providers — OpenAI, Anthropic, and Ollama — with a consistent interface for messages, tool calling, and structured output.

This adapter powers the Level 3 (LLM call) layer in the agent architecture. It can also be invoked directly for one-shot LLM calls.

Backends

Operation	Provider	Default Model	API Key Secret
langchain:openai	OpenAI	gpt-4o-mini	OPENAI_API_KEY
langchain:anthropic	Anthropic	claude-sonnet-4-5-20250514	ANTHROPIC_API_KEY
langchain:ollama	Ollama (local)	qwen	None required
langchain:ollama_qwen3	Ollama (Qwen3)	qwen3	None required

Setting API Keys

Store API keys via the secrets manager:

{ "operation": "secret:set", "input": { "key": "OPENAI_API_KEY", "value": "sk-..." } }
{ "operation": "secret:set", "input": { "key": "ANTHROPIC_API_KEY", "value": "sk-ant-..." } }

Keys are resolved from the caller's secret store at invocation time.

Usage

Simple Prompt

{
  "operation": "langchain:openai",
  "input": {
    "prompt": "What is the capital of France?",
    "model": "gpt-4o"
  }
}

Response: { "response": "The capital of France is Paris." }

Messages with System Prompt

{
  "operation": "langchain:anthropic",
  "input": {
    "model": "claude-sonnet-4-5-20250514",
    "messages": [
      { "role": "system", "content": "You are a helpful assistant." },
      { "role": "user", "content": "Explain lattice technology in one paragraph." }
    ]
  }
}

Response:

{
  "role": "assistant",
  "content": "Lattice technology is a mathematical framework..."
}

Tool Calling

Provide tool definitions and the LLM can request tool calls:

{
  "operation": "langchain:openai",
  "input": {
    "model": "gpt-4o",
    "messages": [
      { "role": "user", "content": "What's the weather in London?" }
    ],
    "tools": [
      {
        "name": "get_weather",
        "description": "Get current weather for a city",
        "parameters": {
          "type": "object",
          "properties": {
            "city": { "type": "string" }
          },
          "required": ["city"]
        }
      }
    ]
  }
}

Response:

{
  "role": "assistant",
  "toolCalls": [
    { "id": "call_abc123", "name": "get_weather", "arguments": { "city": "London" } }
  ]
}

To continue the conversation, execute the tool and send the result back:

{
  "messages": [
    { "role": "user", "content": "What's the weather in London?" },
    { "role": "assistant", "toolCalls": [{ "id": "call_abc123", "name": "get_weather", "arguments": { "city": "London" } }] },
    { "role": "tool", "id": "call_abc123", "name": "get_weather", "content": "{\"temp\": 15, \"condition\": \"cloudy\"}" }
  ],
  "tools": [...]
}

Structured Output

Request JSON output conforming to a schema:

{
  "operation": "langchain:openai",
  "input": {
    "model": "gpt-4o",
    "messages": [
      { "role": "user", "content": "Extract the person's name and age from: 'Alice is 30 years old'" }
    ],
    "responseFormat": {
      "name": "PersonInfo",
      "schema": {
        "type": "object",
        "properties": {
          "name": { "type": "string" },
          "age": { "type": "integer" }
        },
        "required": ["name", "age"],
        "additionalProperties": false
      }
    }
  }
}

The OpenAI backend enables strict mode by default — the response is guaranteed to conform to the schema.

Input Reference

Parameter	Type	Default	Description
prompt	string	—	Simple prompt (alternative to messages)
systemPrompt	string	—	System message (with prompt mode)
messages	array	—	Conversation messages (system, user, assistant, tool)
tools	array	—	Tool definitions for function calling
model	string	Backend default	Model name override
responseFormat	string or object	"text"	"text", "json", or {name, schema}
apiKey	string	From secret store	Override API key
url	string	Backend default	Override API endpoint

Related

• Agents: LLM Backends — configuring backends for agents
• Agents Overview — how LangChain fits in the agent architecture