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

Annotations already declare readOnly/idempotent/non-destructive, and the description adds real behavior beyond them: the returned field set, the meaning of metadata, the empty-caption edge case for password-protected files read by a non-editor, the permission prerequisite, and the not-found failure mode. That is substantive disclosure an agent cannot get from the annotations.

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?

Purpose and return shape are front-loaded, and each sentence carries information. It is somewhat dense — the password-protected caption caveat and the AlphaBridge forwarding note add length — but all of them are useful rather than 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 no output schema, the description takes on the burden of describing the return object and does so ('{id, title, mime, url, alt, caption, metadata}'), plus error and permission behavior. Nothing an agent needs to invoke this single-parameter read 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% and the single 'id' parameter is already documented as 'Attachment id, as wp_list_media returns it.' The description reinforces the origin of the id but adds no format or constraint detail beyond the schema, so the baseline of 3 applies.

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 one file of the media library (attachment) by id') and names the two sibling tools it must not be confused with (wp_get_post for posts/pages, wp_list_media for listings). An agent can select it 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 routes non-media ids away ('An id that is not a media file ... returns a not-found error: posts and pages are read by wp_get_post, and wp_list_media lists the media with their ids'). This gives both the when-to-use and the when-not-to-use plus the alternative, which is the top of the scale.

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