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CrispyW0nton

Chrome Course MCP

by CrispyW0nton

chrome_eval

Run JavaScript code in a selected Chrome tab to inspect page state or automate panel interactions.

Instructions

Evaluate JavaScript in the selected tab. Use for small, explicit inspection or panel automation snippets.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
tabIdNo
waitMsNo
debugUrlNohttp://127.0.0.1:9222
expressionYes
urlContainsNo
titleContainsNo
Behavior2/5

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

With no annotations, the description carries the full burden of disclosing side effects and execution context. It only says 'evaluate JavaScript' but does not state that scripts can modify the page, what the return value looks like, whether the evaluation is asynchronous, or how tab selection works. This leaves significant behavioral ambiguity for an agent invoking the tool.

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 two short sentences, front-loaded with the core action. It provides just enough context in a compact form without extraneous detail. Each sentence adds value: the first states the primary function, the second clarifies the intended use case.

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

Completeness1/5

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

Given the tool has six parameters, no annotations, no output schema, and a complex execution environment, the description is severely under-specified. It lacks any explanation of return values, parameter semantics, tab resolution logic, or side effects. For a tool of this complexity, the description is far from adequate.

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

Parameters1/5

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

Schema description coverage is 0%, and the description mentions none of the six parameters (tabId, waitMs, debugUrl, expression, urlContains, titleContains). It does not explain what 'expression' means, how tab selection is performed, or the roles of waitMs or debugUrl. The description adds no parameter-level insight beyond the schema itself.

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 evaluates JavaScript in the selected tab, using a specific verb ('Evaluate') and resource ('JavaScript in the selected tab'). It also narrows the scope to 'small, explicit inspection or panel automation snippets,' which distinguishes it from sibling tools like chrome_click or chrome_type that perform direct UI actions.

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 provides a clear usage context: 'Use for small, explicit inspection or panel automation snippets.' This implies when the tool is appropriate, but it does not explicitly mention alternatives or when not to use it (e.g., for complex multi-step automation). Thus it stops short of a full when/when-not breakdown.

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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