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

With no annotations provided, the description carries the full burden of behavioral disclosure. It clearly states that the tool fetches the URL, hashes exactly the received bytes, signs the result, and refuses bodies over 2 MB. It does not mention redirects, network error handling, or rate limits, but for a one-parameter tool these are minor omissions. The description is transparent about the core behavior and constraints.

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 sentences with zero filler. The core action is stated first, followed by the use case and a critical constraint. Every sentence earns its place, and the size limit is front-loaded after the main purpose. This is exemplary conciseness.

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 tool with one parameter and no output schema, the description covers the primary function, the reason to use it, and a key limitation. It does not explicitly describe the return format (e.g., that it returns a string hash), but the name and context strongly imply it. It also omits error behavior, but that is a minor gap for a tool of this complexity.

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 input schema already describes the 'url' parameter as 'An http or https URL.' The tool description reinforces that it fetches the URL and hashes it, but adds no new syntactic or semantic details beyond what the schema provides. Since schema coverage is 100%, the baseline is 3, and the description does not elevate it further.

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 a clear verb ('Fetch'), a resource (a public URL), and an outcome (SHA-256 of the bytes, signed). It also states the exact scope of what is hashed ('exactly the bytes received'), which distinguishes it from any normalization or transformation. This makes the tool's purpose unmistakable even without inspecting the schema.

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 a concrete use case: two agents can compare receipts to agree they saw the same file. It also imposes a size limit (bodies over 2 MB are refused), which helps an agent decide if it is appropriate for a given URL. However, it does not explicitly name alternative tools or state when not to use it, leaving some inference to the agent.

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