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debugger-connect

Connect to a JavaScript runtime's CDP debugger on iOS, Android, Vega, or Chromium, returning connection info needed to begin debugging or before using other debugger tools.

Instructions

Connect to a JS runtime CDP debugger. iOS / Android / Vega: connects to Metro's CDP endpoint on the given port. Chromium: re-uses the page CDP session opened by boot-device — port is ignored. Returns connection info including port, projectRoot (empty on Chromium and on legacy Metro, e.g. Vega), deviceName, appName, logicalDeviceId (absent on Vega), and isNewDebugger. If already connected, returns the existing connection. Use when starting a debug session or before calling other debugger-* tools. Fails if the runtime is unreachable (Metro down, or Chromium CDP terminated).

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
portNoMetro server port. Optional — omit it to use this device's port, 8081 by default. Ignored for Chromium, whose CDP port is encoded in device_id.
device_idYesDevice id from list-devices: iOS simulator UDID, Android serial, Vega serial (amazon-...), or Chromium device id (chromium-cdp-<port>). Pass this SAME id as device_id to every subsequent debugger-* call to pin them to this device. The returned logicalDeviceId is informational (Metro's own per-connection handle, absent on Vega); you do not switch to it — forwarding it still resolves here, but the list-devices id is the stable one.

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed5 schema fields changedv0.25.0
    • removedInput schema / properties / port / default
      Removed value: -8081
    • changedInput schema / properties / port / description
      Previous value: -"Metro server port (ignored for Chromium — its CDP port is encoded in device_id)"New value: +"Metro server port. Optional — omit it to use this device's port, 8081 by default. Ignored for Chromium, whose CDP port is encoded in device_id."
    • addedInput schema / properties / port / maximum
      Added value: +65535
    • addedInput schema / properties / port / minimum
      Added value: +1
    • changedInput schema / properties / port / type
      Previous value: -"number"New value: +"integer"
  2. Changed1 schema field changedv0.17.0
    • changedInput schema / properties / device_id / description
      Previous value: -"Device id: iOS simulator UDID, Android logicalDeviceId returned by Metro, Vega serial (amazon-...), or Chromium device id (chromium-cdp-<port>) from list-devices. When a logicalDeviceId is returned, forward it as device_id to all subsequent debugger-* calls to pin them to this device; when none is returned (Vega), keep passing the id you connected with."New value: +"Device id from list-devices: iOS simulator UDID, Android serial, Vega serial (amazon-...), or Chromium device id (chromium-cdp-<port>). Pass this SAME id as device_id to every subsequent debugger-* call to pin them to this device. The returned logicalDeviceId is informational (Metro's own per-connection handle, absent on Vega); you do not switch to it — forwarding it still resolves here, but the list-devices id is the stable one."
  3. Changed1 schema field changedv0.16.0
    • changedInput schema / properties / device_id / description
      Previous value: -"Device id: iOS simulator UDID, Android logicalDeviceId returned by Metro, or Chromium device id (chromium-cdp-<port>) from list-devices. The returned logicalDeviceId must be forwarded as device_id to all subsequent debugger-* calls to pin them to this device."New value: +"Device id: iOS simulator UDID, Android logicalDeviceId returned by Metro, Vega serial (amazon-...), or Chromium device id (chromium-cdp-<port>) from list-devices. When a logicalDeviceId is returned, forward it as device_id to all subsequent debugger-* calls to pin them to this device; when none is returned (Vega), keep passing the id you connected with."
  4. First observedv0.15.0

TDQS

A4.7/5.0
Behavior4/5

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

The description discloses important behavioral traits: it returns existing connection if already connected, ignores port for Chromium, and fails on unreachable runtime. It also explains the return value structure (connection info fields). While annotations are absent, the description carries the burden well by explaining idempotent behavior and failure modes.

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 well-structured with a clear opening sentence, platform-specific details, return value summary, usage guidance, and failure conditions. Every sentence adds value, and the most important information (what it does, when to use it) is front-loaded.

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

Completeness5/5

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

For a connection tool with 2 parameters and no output schema, the description is complete. It covers what the tool does, platform variations, return values, idempotent behavior, usage context, and failure modes. An agent has everything needed to call it correctly.

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

Parameters4/5

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

Schema coverage is 100%, so the schema already documents both parameters. The description adds value by explaining the port's platform-specific behavior (ignored for Chromium) and the device_id's stability guidance ('Pass this SAME id... you do not switch to it'). This goes beyond the schema's basic descriptions.

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 states the tool's purpose: 'Connect to a JS runtime CDP debugger.' It specifies the verb (connect), the resource (JS runtime CDP debugger), and distinguishes between platforms (iOS/Android/Vega vs Chromium). It also differentiates from siblings by noting it's the prerequisite for other debugger-* tools.

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

Usage Guidelines5/5

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

The description explicitly states when to use this tool: 'Use when starting a debug session or before calling other debugger-* tools.' It also provides platform-specific guidance (Chromium re-uses existing session, port ignored) and failure conditions ('Fails if the runtime is unreachable'). This is clear usage guidance with no ambiguity.

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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