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

No annotations provided, so description carries the burden. It discloses the powerful nature ('Power tool'), return type ('JSON-stringified result'), and error behavior. Could mention potential side effects, but sufficient for a single-param tool.

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

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

Three sentences with no redundancy: first states purpose, second gives usage advice, third details parameter options. Information is front-loaded and efficient.

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

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

With one parameter and no output schema, the description covers purpose, usage, return type, and error cases. It omits details like 'last expression' semantics but is adequate for the tool's simplicity.

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

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

Schema has 100% coverage with a clear description for 'code.' The description adds value by specifying alternative param names ('script or expression aliases') and error handling, beyond the schema.

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

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

The description uses a specific verb 'Run arbitrary JavaScript' and identifies the resource 'embedded QuickJS runtime against the current page's parsed DOM.' It clearly differentiates from siblings by advising to prefer query/text/blockmap when a CSS selector suffices.

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

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

Explicit guidance on when to use alternatives ('prefer query/text/blockmap when the CSS selector engine can express what you need') and what happens with incorrect parameters ('errors if no code-like param is present').

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.