Agent Approval

Agents sometimes require the same human-in-the-loop oversight used in workflows when calling tools that handle sensitive operations, like deleting resources or performing running long processes. With agent approval you can suspend a tool call and provide feedback to the user, or approve or decline a tool call based on targeted application conditions.

Tool call approval

Tool call approval can be enabled at the agent level and apply to every tool the agent uses, or at the tool level providing more granular control over individual tool calls.

Storage

Agent approval uses a snapshot to capture the state of the request. Ensure you've enabled a storage provider in your main Mastra instance. If storage isn't enabled you'll see an error relating to snapshot not found.

src/mastra/index.ts

import { Mastra } from "@mastra/core/mastra";
import { LibSQLStore } from "@mastra/libsql";

export const mastra = new Mastra({
  // ...
  storage: new LibSQLStore({
    id: "mastra-storage",
    url: ":memory:"
  })
});

Agent-level approval

When calling an agent using .stream() set requireToolApproval to true which will prevent the agent from calling any of the tools defined in its configuration.

const stream = await agent.stream("What's the weather in London?", {
  requireToolApproval: true
});

Approving tool calls

To approve a tool call, access approveToolCall from the agent, passing in the runId of the stream. This will let the agent know its now OK to call its tools.

const handleApproval = async () => {
  const approvedStream = await agent.approveToolCall({ runId: stream.runId });

  for await (const chunk of approvedStream.textStream) {
    process.stdout.write(chunk);
  }
  process.stdout.write("\n");
};

Declining tool calls

To decline a tool call, access the declineToolCall from the agent. You will see the streamed response from the agent, but it won't call its tools.

const handleDecline = async () => {
  const declinedStream = await agent.declineToolCall({ runId: stream.runId });

  for await (const chunk of declinedStream.textStream) {
    process.stdout.write(chunk);
  }
  process.stdout.write("\n");
};

Tool-level approval

There are two types of tool call approval. The first uses requireApproval, which is a property on the tool definition, while requireToolApproval is a parameter passed to agent.stream(). The second uses suspend and lets the agent provide context or confirmation prompts so the user can decide whether the tool call should continue.

Tool approval using requireToolApproval

In this approach, requireApproval is configured on the tool definition (shown below) rather than on the agent.

export const testTool = createTool({
  id: "test-tool",
  description: "Fetches weather for a location",
  inputSchema: z.object({
    location: z.string()
  }),
  outputSchema: z.object({
    weather: z.string()
  }),
  resumeSchema: z.object({
    approved: z.boolean()
  }),
  execute: async ({ location }) => {
    const response = await fetch(`https://wttr.in/${location}?format=3`);
    const weather = await response.text();

    return { weather };
  },
  requireApproval: true
});

When requireApproval is true for a tool, the stream will include chunks of type tool-call-approval to indicate that the call is paused. To continue the call, invoke resumeStream with the required resumeSchema and the runId.

const stream = await agent.stream("What's the weather in London?");

for await (const chunk of stream.fullStream) {
  if (chunk.type === "tool-call-approval") {
    console.log("Approval required.");
  }
}

const handleResume = async () => {
  const resumedStream = await agent.resumeStream({ approved: true }, { runId: stream.runId });

  for await (const chunk of resumedStream.textStream) {
    process.stdout.write(chunk);
  }
  process.stdout.write("\n");
};

Tool approval using suspend

With this approach, neither the agent nor the tool uses requireApproval. Instead, the tool implementation calls suspend to pause execution and return context or confirmation prompts to the user.

export const testToolB = createTool({
  id: "test-tool-b",
  description: "Fetches weather for a location",
  inputSchema: z.object({
    location: z.string()
  }),
  outputSchema: z.object({
    weather: z.string()
  }),
  resumeSchema: z.object({
    approved: z.boolean()
  }),
  suspendSchema: z.object({
    reason: z.string()
  }),
  execute: async ({ location }, { agent } = {}) => {
    const { resumeData: { approved } = {}, suspend } = agent ?? {};

    if (!approved) {
      return suspend?.({ reason: "Approval required." });
    }

    const response = await fetch(`https://wttr.in/${location}?format=3`);
    const weather = await response.text();

    return { weather };
  }
});

With this approach the stream will include a tool-call-suspended chunk, and the suspendPayload will contain the reason defined by the tool's suspendSchema. To continue the call, invoke resumeStream with the required resumeSchema and the runId.

const stream = await agent.stream("What's the weather in London?");

for await (const chunk of stream.fullStream) {
  if (chunk.type === "tool-call-suspended") {
    console.log(chunk.payload.suspendPayload);
  }
}

const handleResume = async () => {
  const resumedStream = await agent.resumeStream({ approved: true }, { runId: stream.runId });

  for await (const chunk of resumedStream.textStream) {
    process.stdout.write(chunk);
  }
  process.stdout.write("\n");
};

Related

• Using Tools
• Agent Overview
• Tools Overview
• Agent Memory
• Request Context