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chrome-debug-mcp

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open_instance

Open an independent Chrome instance with its own profile and debugging port to isolate browsing sessions, cookies, proxies, or WebMCP contexts; returns instance_id for other tools.

Instructions

Opens a new independent Chrome instance. Side effects: launches a separate Chrome process with its own profile directory and remote-debugging port. Prerequisites: rejected when the server runs in --user-profile mode (Chrome's singleton profile lock). Returns: structured JSON with 'instance_id' (pass it as the 'instance_id' argument of other tools), 'host', 'port' and 'profile_dir'. Use this to isolate browsing sessions, cookies, proxies or WebMCP contexts from one another. Alternatives: 'open_tab' for additional tabs within an existing instance. Parameters: 'features' accepts a closed set - 'WEBGL_SOFTWARE' (forces SwiftShader software WebGL for GPU-less environments); 'headless' defaults to false (prefer false so the user can see the browser).

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
labelNoOptional label to identify the instance. The label becomes the instance_id returned by this tool and accepted by the 'instance_id' argument of other tools. If omitted, a dynamic label is generated.
proxyNoOptional proxy server configuration.
featuresNoOptional feature presets (e.g. WEBGL_SOFTWARE).
headlessNoOptional headless mode. Encouraged to be set to false so that the user can see what happens with the browser. Defaults to false.

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed2 schema fields changedv1.5.1
    • changedInput schema / properties / features / description
      Previous value: -"Optional feature presets (e.g. WEB_MCP, WEBGL_SOFTWARE)."New value: +"Optional feature presets (e.g. WEBGL_SOFTWARE)."
    • changedInput schema / properties / features / items / enum
      Previous value: -[
-  "WEB_MCP",
-  "WEBGL_SOFTWARE"
-]New value: +[
+  "WEBGL_SOFTWARE"
+]
  2. Changed7 schema fields changedv1.3.2
    • addedInput schema / properties / features / items / enum
      Added value: +[
+  "WEB_MCP",
+  "WEBGL_SOFTWARE"
+]
    • removedInput schema / properties / features / items / oneOf
      Removed value: -[
-  {
-    "enum": [
-      "WEB_MCP"
-    ]
-  },
-  {
-    "enum": [
-      "WEBGL_SOFTWARE"
-    ]
-  }
-]
    • addedInput schema / properties / features / items / type
      Added value: +"string"
    • removedInput schema / properties / features / nullable
      Removed value: -true
    • removedInput schema / properties / headless / nullable
      Removed value: -true
    • removedInput schema / properties / label / nullable
      Removed value: -true
    • removedInput schema / properties / proxy / nullable
      Removed value: -true
  3. Addedv1.0.11

TDQS

A4.8/5.0
Behavior5/5

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

With no annotations, the description carries the full burden and does so well: it discloses side effects (separate Chrome process, own profile directory and remote-debugging port), a prerequisite failure mode (rejected under --user-profile due to Chrome's singleton lock), and the return shape.

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

Conciseness4/5

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

Purpose is front-loaded, then side effects, prerequisites, returns, usage, and alternatives in a logical order. It is dense but nearly every clause carries information; minor compression is possible in the parameter section.

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?

Covers purpose, when-to-use, alternatives, side effects, prerequisites, and return values with no output schema present. Everything an agent needs to decide and call correctly is present.

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 description coverage is 100%, so the baseline is 3, but the description adds meaning beyond the schema: it explains what WEBGL_SOFTWARE does (forces SwiftShader for GPU-less environments) and the default/rationale for headless. Proxy and label mapping to instance_id are largely covered by the schema.

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?

States a specific verb and resource ('Opens a new independent Chrome instance') and distinguishes it from the sibling 'open_tab', which creates tabs within an existing instance. The 'independent' qualifier sets the scope precisely.

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?

Explicitly states when to use it ('to isolate browsing sessions, cookies, proxies or WebMCP contexts') and names the alternative ('open_tab' for additional tabs within an existing instance). It also states a prerequisite rejection condition (--user-profile mode).

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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