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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the safety profile is covered. The description adds that the link is short-lived, which is useful, but it does not mention that each call produces a distinct URL (idempotentHint=false) or whether auth on the resulting URL is embedded or required.

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?

Two tight sentences with the output front-loaded and the usage rule second. Nothing is redundant or padded.

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 read-only presign tool with no output schema, the description conveys the return artifact and the primary use case. It leaves out whether the response also carries the expiry metadata, but the schema's expiresInMinutes note partly covers that.

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%, and every parameter — including the expiry clamping behavior — is documented in the schema itself. The description adds no parameter-level meaning beyond that, so the baseline 3 applies.

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 concrete deliverable — a pre-signed URL for downloading an object — and implicitly separates itself from read_object with 'instead of reading them.' It is specific enough to distinguish the tool, though it does not name the sibling it replaces outright.

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?

'Use for binary or large objects instead of reading them' gives a clear selection condition and an implied alternative (reading the object via the read path). It stops short of stating when this is inappropriate, such as when the object is small or when the bytes are needed in-process.

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