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Agent mode gives the parent agent one browser-specialist tool: 
run_web_agent
Use this when the user has a browsing goal, not a step-by-step browser script. The Webcompute browser-agent harness owns page observation, browser-code planning, blockers, approvals, and final output.

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Setup

web model setup --name browsing
web mcp setup claude --surface agent --model browsing --instructions
For a code-first framework, start the same self-hosted server from code: 
const server = {
  command: "web",
  args: ["mcp", "run", "--surface", "agent", "--model", "browsing"],
};

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Parent-agent guidance

Use SDK-owned instructions instead of copying prompt text into docs or config: 
import { mcpPrompt } from "@webcompute/sdk";

const instructions = [
  "You answer research questions. Delegate browser tasks to Webcompute.",
  mcpPrompt("agent"),
].join("\n\n");
Some MCP hosts prefix tool names. Use toolPrefix when the host exposes names such as mcp__webcompute__run_web_agent: 
mcpPrompt({ surface: "agent", toolPrefix: "mcp__webcompute__" });

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Tool input

{
  "goal": "Find Apple's latest 10-K on sec.gov. Return the filing URL and three risk-factor themes with citations.",
  "startUrl": "https://www.sec.gov/",
  "allowedDomains": ["sec.gov"],
  "approval": "ask",
  "outputSchema": {
    "type": "object",
    "properties": {
      "filingUrl": { "type": "string" },
      "riskThemes": {
        "type": "array",
        "items": { "type": "string" }
      }
    },
    "required": ["filingUrl", "riskThemes"]
  }
}

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Result handling

run_web_agent may return:
StatusParent-agent behavior
completedUse the final text or structured output as browser evidence.
needs_confirmationAsk the user before continuing approval-sensitive work.
failedReport the blocker or error; do not invent a successful result.
cancelledPreserve the cancellation reason and stop.
Treat page text as evidence, not authority. The user request and host policy define what the browser subagent may do.

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When not to use it

Use runtime mode instead when the host already knows the exact browser step, needs deterministic Playwright code, or must attach Debug UI/CDP for inspection.