fetch_url

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

With no annotations provided, the description carries the full burden. It discloses the behavior well by listing all parameters (timeout, follow_redirects, user_agent) and the return structure (status_code, content, headers, encoding, error). It does not go into deeper detail about network failure modes, but the presence of an 'error' field adds transparency.

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 well-structured: a one-line summary, an Args block with each parameter explained, and a Returns block. Every sentence adds value, and it is appropriately sized for the tool's complexity.

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?

For a basic URL fetching tool with an output schema, the description is largely complete. It covers all parameters and the return value. It doesn't mention usage context relative to siblings or note any special behavior like redirect handling beyond the boolean parameter, but given the output schema and simple nature, it is sufficiently complete.

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 description coverage is 0%, so the description is the sole source of parameter meaning. It explains each parameter beyond the schema's type/default: timeout is 'in seconds', user_agent is a 'custom user agent string (optional)', and follow_redirects is 'whether to follow redirects.' This fully compensates for the lack of schema descriptions.

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 clearly states the tool's action: 'Fetches content from a URL.' It is specific and unambiguous, but it does not explicitly differentiate from the sibling tool 'fetch_with_headers', so it lacks sibling distinction.

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 provides no guidance on when to use this tool versus alternatives like 'fetch_with_headers'. It does not state whether to use it for simple fetches or when custom headers are needed. The intended usage is only implied through the basic action description.

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