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

Annotations declare readOnlyHint=false and idempotentHint=false, but the description adds real behavioral context the annotations cannot express: Content-Type and Content-Length must exactly match the announced values, and any mismatch yields a 403 from storage. It does not mention URL expiry or auth prerequisites, which is the main remaining gap for a presigned-URL tool.

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 short sentences, front-loaded with the outcome, then the constraint, then the sequence. Every clause carries actionable information; nothing is restated from the title or 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 5-required-param, no-output-schema tool, the description fully covers the return value (URL plus headers) and the downstream sequence, plus the 403 failure mode. It omits URL lifetime/expiry and permission requirements, which an agent would want before retrying or batching.

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 coverage is only 40%, so the description must compensate, and it does for the two riskiest parameters: content_type and size_bytes are pinned as the exact values the URL is bound to. It adds nothing about filename beyond the schema's pattern, but the marginal value over structured fields is substantial.

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 and resource ('Get a presigned PUT URL for one file') and immediately situates it as step 1 of a 3-step upload flow, which distinguishes it from attach_file and get_download_url among the many siblings. An agent can tell what it produces 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?

Explicitly names the workflow position ('Step 1 of 3'), the intermediate action ('then PUT the bytes to that URL'), and the follow-up tool ('then call attach_file'). The alternative path is unambiguous, leaving no inference about ordering.

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