fetch_url

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

No annotations are provided, so the description must fully disclose behavioral traits. It does mention the return size limit ('up to 100KB'), but this conflicts with the schema's max_bytes property which allows up to 1MB, creating ambiguity. The description also does not address response format, error behavior, redirects, or authentication, leaving key behavioral characteristics undefined.

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 just two sentences, with the action front-loaded. Every sentence adds value: the first states the core function, the second notes the size limit and common use cases. There is no redundant or filler content.

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 simple fetch tool with a documented schema and no output schema, the description is mostly adequate. However, it omits details about what 'text content' means (raw HTML vs extracted text), how errors are surfaced, and the fact that the 100KB limit is only the default and can be increased. These omissions, combined with the size-limit ambiguity, prevent a higher score.

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 provides descriptions for all three parameters, with 100% coverage. The description does not add any parameter-specific detail beyond what is already in the schema; it only generalizes about the return size. Per the rubric, with high schema coverage, the baseline score is 3.

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 begins with a specific verb+resource pair: 'Fetch the text content of a URL.' This clearly distinguishes the tool from its sibling 'echo', which simply echoes input. The mention of HTTP endpoints further clarifies the tool's scope.

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 usage context by stating it is 'Useful for reading web pages, APIs, or any HTTP endpoint.' However, it does not explicitly state when not to use the tool or mention alternatives beyond the sibling 'echo', which is clearly not an alternative. This earns a 4 for clear context without explicit exclusions.

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