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

With no annotations provided, the description carries the full burden of disclosing behavior. It clearly states the URL expires in five minutes, that the stored file does not expire, that the URL is what travels (never credentials), and that it's a deliberate two-step process. This gives an agent a clear model of what happens without needing annotations.

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 and front-loaded with the core function. It repeats the expiration point twice (once at the start and once at the end), which is slightly redundant, but the overall length is appropriate and no unnecessary words are present. It earns a 4 because the repetition is minor.

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 4-parameter getter with no output schema, the description covers the essential aspects: what it returns (a signed URL), the expiration behavior, and the security rationale. It doesn't detail the exact response structure, but that's often not needed for a URL-returning tool. It also doesn't mention error conditions or prerequisites, but the tool's simplicity and the schema's clarity make it reasonably 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 100%, so each parameter already has a descriptive label. The description adds the concept of 'by its index' but doesn't enrich parameter meaning beyond what the schema provides. For example, it doesn't explain the format of 'index' or how to obtain it, but the schema's 'from the message' is sufficient. The baseline of 3 applies because the schema does the heavy lifting.

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 states a specific action ('Get a five-minute signed URL for one attachment'), identifies the resource (attachment in a message), and the selection method (by index). It clearly distinguishes itself from sibling tools by focusing on a single attachment's temporary URL, which is a unique capability among the inbox-related tools.

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 explains the purpose of the two-step process and the tradeoff (URL expires, file doesn't), which conveys when this tool is appropriate (when a temporary, safe URL is needed) and implies when it's not (when persistent access is required). However, it doesn't explicitly name alternative tools or provide exclusionary guidance, so it's not a full 5.

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