agent-browser-mcp

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network_capture_start

Destructive

Start capturing network requests and responses from a browser tab in the background. Returns a buffer of captured traffic, including response bodies, for analysis without interrupting the active page.

Instructions

Start bounded CDP Network capture on a real-browser tab. Captures requests, responses, and optionally response bodies without foregrounding the tab. Call network_capture_stop from this same MCP session to return the buffer and release the debugger lease. Another session's capture returns capture_busy; use a separate tab per agent.

Tool call template

This tool declares no required parameters. Add optional parameters from the input schema as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {},
    "name": "network_capture_start"
  }
}

Input Schema

Name	Required	Description	Default
`timeout`	No
`session_id`	No
`max_entries`	No
`body_timeout`	No
`include_bodies`	No
`max_body_bytes`	No

Output Schema

Name	Required	Description	Default
No arguments

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.1.0Sep 5, 2026

TDQS

A4.3/5.0

Behavior5/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Beyond the annotations, the description discloses several important behaviors: the capture is bounded, it does not foreground the tab, it acquires a debugger lease that must be released via network_capture_stop, and another session's capture will return capture_busy. This is exactly the practical behavioral context an agent needs.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is three tight sentences with no filler. It front-loads the action and output, then immediately provides the critical stop-and-concurrency instructions. Every sentence earns its place.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

An output schema existsbool and all parameters are optional with defaults, so the default invocation path is well covered. The main gap is parameter-level detail for custom capture limits and session_id, but the description supplies the most important lifecycle and concurrency context.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters2/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 0%, and the description only vaguely addresses parameters: 'optionally response bodies' hints at include_bodies alert and 'bounded' hints at limits. It does not explain timeout, session_id, max_entries, body_timeout, or max_body_bytes, so the agent must rely on parameter names and defaults.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly identifies the verb ('Start'), the resource ('CDP Network capture'), and the target context ('real-browser tab'). It also states exactly what is captured ('requests, responses, and optionally response bodies'), making it easy to distinguish from network_capture_stop and console_capture_start.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description gives explicit lifecycle guidance: call network_capture_stop from the same session to retrieve the buffer and release the debugger lease. It also warns about concurrent sessions returning capture_busy and directs the agent to use a separate tab per agent. It does not contrast this with related tools like console_capture_start, but the operational context is strong.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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