Interface●Since v1.1

AgentMiddleware

Base middleware interface.

interface AgentMiddleware

Example

const middleware = createMiddleware({
  name: "myMiddleware",
  stateSchema: z.object({ count: z.number() }),
  tools: [myTool],
});

Properties

property

[MIDDLEWARE_BRAND]: true

Brand property to distinguish middleware instances from plain objects or functions. This is required and prevents accidental assignment of functions to middleware arrays.

property

afterAgent: AfterAgentHook<TSchema, TFullContext>

The function to run after the agent execution completes. This function is called once at the end of the agent invocation. It allows to modify the final state of the agent after all model calls and tool executions are complete.

property

afterModel: AfterModelHook<TSchema, TFullContext>

The function to run after the model call. This function is called after the model is invoked and before any tools are called. It allows to modify the state of the agent after the model is invoked, e.g. to update tool call parameters.

property

beforeAgent: BeforeAgentHook<TSchema, TFullContext>

The function to run before the agent execution starts. This function is called once at the start of the agent invocation. It allows to modify the state of the agent before any model calls or tool executions.

property

beforeModel: BeforeModelHook<TSchema, TFullContext>

The function to run before the model call. This function is called before the model is invoked and before the wrapModelCall hook. It allows to modify the state of the agent.

property

contextSchema: TContextSchema

The schema of the middleware context. Middleware context is read-only and not persisted between multiple invocations. It can be either:

A Zod object
A Zod optional object
A Zod default object
Undefined

property

name: string

The name of the tool being called

property

stateSchema: TSchema

The schema of the middleware state. Middleware state is persisted between multiple invocations. It can be either:

A Zod object (InteropZodObject)
A StateSchema from LangGraph (supports ReducedValue, UntrackedValue)
An AnnotationRoot
Undefined

property

tools: TTools

property

wrapModelCall: WrapModelCallHook<TSchema, TFullContext>

Wraps the model invocation with custom logic. This allows you to:

Modify the request before calling the model
Handle errors and retry with different parameters
Post-process the response
Implement custom caching, logging, or other cross-cutting concerns

wrapModelCall: async (request, handler) => {
  // Modify request before calling
  const modifiedRequest = { ...request, systemPrompt: "You are helpful" };

  try {
    // Call the model
    return await handler(modifiedRequest);
  } catch (error) {
    // Handle errors and retry with fallback
    const fallbackRequest = { ...request, model: fallbackModel };
    return await handler(fallbackRequest);
  }
}

property

wrapToolCall: WrapToolCallHook<TSchema, TFullContext>

Wraps tool execution with custom logic. This allows you to:

Modify tool call parameters before execution
Handle errors and retry with different parameters
Post-process tool results
Implement caching, logging, authentication, or other cross-cutting concerns
Return Command objects for advanced control flow

The handler receives a ToolCallRequest containing the tool call, state, and runtime, along with a handler function to execute the actual tool.

wrapToolCall: async (request, handler) => {
  console.log(`Calling tool: ${request.tool.name}`);
  console.log(`Tool description: ${request.tool.description}`);

  try {
    // Execute the tool
    const result = await handler(request);
    console.log(`Tool ${request.tool.name} succeeded`);
    return result;
  } catch (error) {
    console.error(`Tool ${request.tool.name} failed:`, error);
    // Could return a custom error message or retry
    throw error;
  }
}

wrapToolCall: async (request, handler) => {
  // Check if user is authorized for this tool
  if (!request.runtime.context.isAuthorized(request.tool.name)) {
    return new ToolMessage({
      content: "Unauthorized to call this tool",
      tool_call_id: request.toolCall.id,
    });
  }
  return handler(request);
}

const cache = new Map();
wrapToolCall: async (request, handler) => {
  const cacheKey = `${request.tool.name}:${JSON.stringify(request.toolCall.args)}`;
  if (cache.has(cacheKey)) {
    return cache.get(cacheKey);
  }
  const result = await handler(request);
  cache.set(cacheKey, result);
  return result;
}

View source on GitHub

Properties

property

[MIDDLEWARE_BRAND]: true

Brand property to distinguish middleware instances from plain objects or functions. This is required and prevents accidental assignment of functions to middleware arrays.

property

afterAgent: AfterAgentHook<TSchema, TFullContext>

property

afterModel: AfterModelHook<TSchema, TFullContext>

property

beforeAgent: BeforeAgentHook<TSchema, TFullContext>

property

beforeModel: BeforeModelHook<TSchema, TFullContext>

The function to run before the model call. This function is called before the model is invoked and before the wrapModelCall hook. It allows to modify the state of the agent.

property

contextSchema: TContextSchema

The schema of the middleware context. Middleware context is read-only and not persisted between multiple invocations. It can be either:

A Zod object
A Zod optional object
A Zod default object
Undefined

property

name: string

The name of the tool being called

property

stateSchema: TSchema

The schema of the middleware state. Middleware state is persisted between multiple invocations. It can be either:

A Zod object (InteropZodObject)
A StateSchema from LangGraph (supports ReducedValue, UntrackedValue)
An AnnotationRoot
Undefined

property

tools: TTools

property

wrapModelCall: WrapModelCallHook<TSchema, TFullContext>

Wraps the model invocation with custom logic. This allows you to:

Modify the request before calling the model
Handle errors and retry with different parameters
Post-process the response
Implement custom caching, logging, or other cross-cutting concerns

wrapModelCall: async (request, handler) => {
  // Modify request before calling
  const modifiedRequest = { ...request, systemPrompt: "You are helpful" };

  try {
    // Call the model
    return await handler(modifiedRequest);
  } catch (error) {
    // Handle errors and retry with fallback
    const fallbackRequest = { ...request, model: fallbackModel };
    return await handler(fallbackRequest);
  }
}

property

wrapToolCall: WrapToolCallHook<TSchema, TFullContext>

Wraps tool execution with custom logic. This allows you to:

Modify tool call parameters before execution
Handle errors and retry with different parameters
Post-process tool results
Implement caching, logging, authentication, or other cross-cutting concerns
Return Command objects for advanced control flow

The handler receives a ToolCallRequest containing the tool call, state, and runtime, along with a handler function to execute the actual tool.

wrapToolCall: async (request, handler) => {
  console.log(`Calling tool: ${request.tool.name}`);
  console.log(`Tool description: ${request.tool.description}`);

  try {
    // Execute the tool
    const result = await handler(request);
    console.log(`Tool ${request.tool.name} succeeded`);
    return result;
  } catch (error) {
    console.error(`Tool ${request.tool.name} failed:`, error);
    // Could return a custom error message or retry
    throw error;
  }
}

wrapToolCall: async (request, handler) => {
  // Check if user is authorized for this tool
  if (!request.runtime.context.isAuthorized(request.tool.name)) {
    return new ToolMessage({
      content: "Unauthorized to call this tool",
      tool_call_id: request.toolCall.id,
    });
  }
  return handler(request);
}

const cache = new Map();
wrapToolCall: async (request, handler) => {
  const cacheKey = `${request.tool.name}:${JSON.stringify(request.toolCall.args)}`;
  if (cache.has(cacheKey)) {
    return cache.get(cacheKey);
  }
  const result = await handler(request);
  cache.set(cacheKey, result);
  return result;
}

AgentMiddleware

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AgentMiddleware

Example

Properties