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

Annotations only declare the safety profile (not read-only, not idempotent, not destructive); the description adds substantive facts the agent cannot get elsewhere: the URL expires in one hour, the caller must PUT raw bytes with a Content-Length header, and the returned file_id must be forwarded to process_images. It also notes the operation is free, which matters for an agent deciding whether to route a large file this way.

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 sentences, zero waste: the first establishes purpose and eligibility, the second gives the exact call sequence. Size limits and the critical PUT instruction are front-loaded rather than buried.

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?

Even though an output schema exists, the description still tells the agent what to do with the returned upload_url and file_id, which is the non-obvious part of the contract. Combined with the expiry window and size bound, nothing an agent needs to invoke this correctly is missing.

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 both 'bytes' and 'filename' are already documented in the schema. The description restates the size ceiling implied by the schema but says nothing about 'filename' or how the declared byte count relates to the actual PUT payload. Baseline 3 is appropriate when the schema carries the parameter detail.

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 one-hour signed upload URL') and immediately scopes it to images/zips over 3 MB up to 100 MB or files already on disk. This clearly separates it from inline submission and from the sibling process_images, which is named as the downstream consumer.

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?

Gives explicit selection criteria (>3 MB, up to 100 MB, or already on disk) that route the agent here rather than to inline sending, and names the alternative tool to call next ('pass file_id to process_images'). The full workflow is spelled out with no inference required.

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