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

Annotations already declare idempotentHint=true and destructiveHint=true; the description reinforces idempotency ('ask again... costs nothing, parts already uploaded stay uploaded') and adds the short-lived URL constraint. It never explains what makes the operation destructive (e.g., that presigned PUTs can overwrite an existing part), which is exactly the context annotations cannot convey.

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?

Three tight sentences, front-loaded with what the tool returns, then the workflow obligation, then the recovery path. No filler and nothing repeated from the schema.

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 six-parameter tool with no output schema, the description covers the obligation loop (upload, keep ETags, re-request) that an agent needs to use it correctly. It does not describe the shape of the returned URL list, though the ETag/response contract is implied well enough for this workflow.

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 all six parameters, including the expiresInMinutes clamping behavior, are documented in the schema itself. The description only alludes to part numbers and adds no format or constraint detail beyond the schema, 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?

States a specific verb+resource ('pre-signed PUT URLs') with the exact scope ('for the part numbers given'), which cleanly separates it from start_multipart_upload and complete_multipart_upload in the sibling list. An agent can identify the tool without opening 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?

Lays out the whole multipart workflow: upload each part yourself, retain the ETag, every ETag is required at completion, and re-request any expired URL. It also says re-requesting is free and non-destructive, so the agent knows the fallback path when a URL expires.

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