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chrome-debug-mcp

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capture_screenshot

Capture a screenshot of the current page viewport or full page as a base64-encoded image to visually verify UI state, layout, or rendering. Specify format and quality for PNG, JPEG, or WebP output.

Instructions

Captures a visual representation of the current page viewport or entire page as a base64 encoded image ('full_page' defaults to false, capturing only the visible viewport; set true to capture the entire page). Side effects: none (read-only). Prerequisites: requires an active Chrome tab. Returns: base64 encoded image in specified format. Use this to visually verify UI state, layout, or rendering. Alternatives: 'inspect_dom' for raw HTML structure, 'get_performance_metrics' for rendering metrics.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
formatNoOutput image format. Constraints: must be 'png', 'jpeg', or 'webp'. Interactions: 'quality' applies only to 'jpeg' and 'webp' formats. Defaults to: "png".
tab_idNoThe Tab ID of the target tab. Omit to use the active tab.
qualityNoCompression quality (0-100, higher=better quality). Constraints: integer between 0 and 100. Interactions: only applies when 'format' is 'jpeg' or 'webp'; ignored for 'png'. Defaults to: 100.
full_pageNoCapture the entire page beyond visible viewport. Constraints: boolean value. Interactions: if true, captures full page height; if false, captures only visible area. Defaults to: false.
instance_idNoChrome instance id from open_instance/list_instances. Omit for the default instance.

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed5 schema fields changedv1.3.2
    • removedInput schema / properties / format / nullable
      Removed value: -true
    • removedInput schema / properties / full_page / nullable
      Removed value: -true
    • removedInput schema / properties / instance_id / nullable
      Removed value: -true
    • removedInput schema / properties / quality / nullable
      Removed value: -true
    • removedInput schema / properties / tab_id / nullable
      Removed value: -true
  2. Changed2 schema fields changedv1.0.11
    • addedInput schema / properties / instance_id
      Added value: +{
+  "description": "Chrome instance id from open_instance/list_instances. Omit for the default instance.",
+  "nullable": true,
+  "type": "string"
+}
    • addedInput schema / properties / tab_id
      Added value: +{
+  "description": "The Tab ID of the target tab. Omit to use the active tab.",
+  "nullable": true,
+  "type": "string"
+}
  3. Changed3 schema fields changedv1.0.7
    • changedInput schema / properties / format / description
      Previous value: -"Optional: Image format. Valid options: \"png\", \"jpeg\", \"webp\". Defaults to \"png\"."New value: +"Output image format. Constraints: must be 'png', 'jpeg', or 'webp'. Interactions: 'quality' applies only to 'jpeg' and 'webp' formats. Defaults to: \"png\"."
    • changedInput schema / properties / full_page / description
      Previous value: -"Optional: Capture the full page layout (beyond the visible viewport). Defaults to false."New value: +"Capture the entire page beyond visible viewport. Constraints: boolean value. Interactions: if true, captures full page height; if false, captures only visible area. Defaults to: false."
    • changedInput schema / properties / quality / description
      Previous value: -"Optional: JPEG or WEBP compression quality (0-100)."New value: +"Compression quality (0-100, higher=better quality). Constraints: integer between 0 and 100. Interactions: only applies when 'format' is 'jpeg' or 'webp'; ignored for 'png'. Defaults to: 100."
  4. First observedv1.0.0

TDQS

A4.7/5.0
Behavior5/5

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

No annotations are provided, so the description carries the full burden. It explicitly states 'Side effects: none (read-only)', the prerequisite of an active Chrome tab, and the return type (base64 encoded image). It also clarifies the full_page behavior. This is exceptionally transparent for a tool without annotations.

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 compact yet structured with clear labels (Side effects, Prerequisites, Returns, Alternatives). Every sentence earns its place, and there is no filler or repetition beyond a minor but acceptable mention of base64 in the first and Returns sentences.

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?

This is a mutating? no, read-only tool with no output schema and no annotations. The description covers side effects, prerequisites, return value, common use case, and alternatives. For a screenshot tool with 5 optional parameters and no output schema, this is complete enough for an agent to call it correctly and interpret the result.

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

Parameters3/5

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

Schema description coverage is 100% with each parameter already providing defaults, constraints, and interactions. The description adds no new parameter-level meaning beyond what the schema states—it only mirrors full_page behavior and mentions base64 output. Per the rubric, baseline 3 applies when the schema does the heavy lifting.

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 uses a specific verb ('Captures') and resource ('visual representation of the current page viewport or entire page'), and states the output as a base64 encoded image. It also explicitly names alternatives (inspect_dom, get_performance_metrics), making the tool's unique purpose clear.

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 the tool ('Use this to visually verify UI state, layout, or rendering') and provides alternatives with their specific use cases ('inspect_dom for raw HTML structure', 'get_performance_metrics for rendering metrics'). It also notes the prerequisite of an active Chrome tab, giving clear operational context.

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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