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

Annotations already declare readOnlyHint, idempotentHint and openWorldHint, so safety is covered. The description adds real behavior beyond that: the `checked: false` lazy state, that size is only read when `open_photo` first opens a photo, and that uploads aggregate across any signed-in connection. This is meaningful extra context, though return-format specifics are largely delegated to the output schema.

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?

It opens with the front-loaded 'Read-only.' and then walks the modes in order, with each sentence carrying specific information. It is slightly dense and longer than strictly necessary, but nothing is pure filler.

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 and annotations covering the safety profile, the description only needs to explain mode selection and edge cases, which it does thoroughly (lazy size, cross-connection uploads, server scoping). Nothing an agent needs in order to call it 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 coverage is 100%, so the baseline is 3. The description goes further by explaining the semantics of each `what` value in terms of the returned data (image ids vs upload handles/sizes/expires_at vs font names) and confirms `filter` applies only to fonts, adding meaning beyond the raw enum values.

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 gives a specific verb ('lists') for each distinct resource selected by the `what` enum: open photos by image id, uploads with handles/sizes/expires_at, and installed fonts. It cleanly enumerates the three modes so an agent knows exactly what it returns, and it references `open_photo` to distinguish the read path from the open path.

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?

Usage is clear: the `what` value selects the mode and `filter` narrows fonts, with the description explaining each context. It also scopes ownership ('uploads and open photos belong to this server; a photo opened through another connector stays with that connector'), which helps decide relevance. It stops short of explicitly naming when to prefer this over siblings like status/overview or check_listing.

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