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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint=false, so the safety profile is covered. The description adds genuinely useful behavior beyond that: result ordering (newest first), scope (only media already in activities), and the key limitation that file contents are not describable from this list — which prevents an agent from fabricating descriptions.

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 with no filler; the scope and ordering constraint is front-loaded, and the second sentence is purely the routing rule. Every clause carries information an agent needs.

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 no output schema, the description could be expected to explain the return shape; it does state ordering and, importantly, that the listing carries no content information, which is the main thing an agent would otherwise misinterpret. Pagination details are left to the schema, which is a minor gap for a list 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 description coverage is 100%, so kind, page, and query are each already documented in the schema, making 3 the correct baseline. The description adds no filtering syntax, default page size, or pagination behavior beyond what the schema states, so it neither compensates nor detracts.

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?

Names a specific verb and resource (listing the user's existing media files) and immediately scopes it: only files already attached to activities, newest first, with no semantic relation to what they show. It also explicitly separates itself from the sibling search_image_library, so an agent can route correctly without opening either 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?

Gives a clear selection rule: use this when the user just needs to point at one of their own files, and use search_image_library when the goal is choosing an image for text. That is explicit alternative-routing, though it does not address the other media-adjacent siblings (attach_video, set_item_images, remove_item_media) that could also be confused with it.

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