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Fast Browser MCP

Fast Browser MCP

by kqlio67
OverviewSchemaSourceRelated ServersDiscussionsAdmin
Python
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browser_observe_coverage

Measure precise V8 JavaScript coverage during execution to discover which scripts and functions actually ran, with optional URL filters and call counts.

Instructions

Measure and observe precise V8 JavaScript code coverage during execution to discover which scripts and functions actually ran.

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": "browser_observe_coverage"
  }
}

Input Schema

NameRequiredDescriptionDefault
detailedNoCollect block-level precise coverage
call_countNoCount function executions
url_filterNoOptional substring filter for script URLs
duration_msNoObservation window duration in milliseconds
only_executedNoOnly return scripts and functions that were actually executed (call count > 0)

Schema Changelog

Changes observed during successful MCP inspections.

  1. Addedv0.12.0

TDQS

C2.9/5.0
Behavior2/5

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

No annotations exist, so the description carries the full burden, yet it discloses none of the important behaviors: whether coverage collection must already be running, whether this call blocks for the observation window, whether it resets previously collected data, or what the result contains. 'During execution' hints at timing but is not actionable.

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?

A single tight sentence with the resource and outcome front-loaded and no filler. It is arguably too short rather than too long, but structurally efficient.

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

Completeness2/5

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

A five-parameter, no-annotation, no-output-schema tool with two obvious sibling coverage tools warrants more: prerequisite lifecycle (start before observe), duration semantics, and whether results accumulate. None of that is covered, so an agent could easily misuse it.

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%, so all five parameters (detailed, call_count, url_filter, duration_ms, only_executed) are already documented in the schema. The description only loosely gestures at only_executed ('which scripts and functions actually ran') and adds no syntax, defaults, or interaction guidance beyond the schema.

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

Purpose4/5

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

States a specific verb+resource: measure/observe V8 JavaScript code coverage during execution, plus the outcome (which scripts and functions actually ran). However, it does not differentiate itself from the closely related siblings browser_start_coverage and browser_stop_coverage, leaving ambiguity about which of the three to call.

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

Usage Guidelines2/5

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

No when-to-use guidance is given, and crucially no mention of how this relates to browser_start_coverage/browser_stop_coverage. An agent cannot tell from the description whether it must call start_coverage first, whether this tool stops collection, or how it differs from the stop tool.

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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