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

Annotations already declare readOnly, idempotent, non-destructive, closed-world behavior, so the bar is lower. The description still adds real value beyond them by disclosing that the return is a private download endpoint rather than the image itself, and that the same Bearer credential must be reused.

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 short sentences, front-loaded with the core purpose followed immediately by the critical caveat about credentials and the non-public nature of the result. Nothing is redundant.

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?

With an output schema present, the description need not explain return values, and it does cover the main trap (private endpoint, auth required). It falls slightly short by not explaining when guestToken is used or where photoId comes from, but overall it is adequate for a two-parameter read tool.

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 50%: guestToken is documented in the schema, while photoId carries only a UUID format and pattern. The description's credential sentence partially addresses the auth parameters, indicating the Bearer path is the default, but it never mentions photoId or the guestToken alternative, so it does not fully compensate for the coverage gap.

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 names a specific verb and resource: retrieving the private JPEG download endpoint for an uploaded photo. It implicitly distinguishes itself from list_photos and create_upload by describing a single-photo fetch, though it never names a sibling explicitly.

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?

It gives useful auth context ('send the same Bearer credential') and warns that this is not a public image URL, which implies usage as an authenticated fetch rather than embedding. However, it never says when to prefer this over list_photos or how to obtain a photoId, leaving selection guidance implied.

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