fetch_url_metadata

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

Annotations include readOnlyHint=true and openWorldHint=true, but the description adds crucial behavioral detail beyond that: it explicitly states that HTTP error status codes do not raise exceptions, while transport-level failures do. This is valuable, non-obvious behavior that informs the agent's error handling.

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?

The description is two short paragraphs. The first sentence states the core purpose immediately, and the second paragraph explains error-handling behavior without any fluff or redundancy. Every sentence earns its place.

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?

This is a simple tool with only two well-documented parameters and an output schema. The description covers the main purpose and the critical edge case of HTTP error handling, making it complete enough for an agent to select and invoke the tool correctly.

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?

The schema already covers both parameters with clear descriptions (URL and timeout_seconds), and schema_description_coverage is 100%. The description does not add meaningful parameter semantics beyond what the schema provides, so the baseline score of 3 is appropriate.

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 opens with 'Fetch a URL and report its status code, content type/length, and response time,' which is a specific verb+resource pair. It clearly distinguishes this tool from siblings like analyze_text and convert_temperature, which serve entirely different purposes.

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?

The description gives clear context for when to use the tool (checking URL metadata) and explains behavior on HTTP errors versus transport failures, effectively setting expectations. However, it does not explicitly mention alternatives or exclusion criteria, falling just short of a 5.

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