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

Annotations already cover read-only/idempotent safety, so the description's job is to add entitlement and output-lifetime context — which it does: a $19/month Library Pro requirement and 1-hour expiring download links. Those are non-obvious operational facts an agent cannot get from the schema or annotations. It stops short of saying what happens on a missing subscription or a failed slug.

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?

Three short sentences, no filler, with the output content and expiry front-loaded before the prerequisite and the parameter hint. Every sentence carries distinct information.

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?

For a single-parameter read tool with no output schema, it covers return content, link lifetime, entitlement requirement, and input source — essentially everything needed to call it correctly. Only error/failure behavior on missing entitlement is absent, which is minor here.

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 earns above that by telling the agent exactly where the slug value comes from (list_directory_apps), which the schema's 'instagram' example does not.

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 the resource precisely (App Store preview videos for a library app) and what comes back (1-hour download links to mp4 files), which is enough to distinguish it from get_screenshots and get_directory_screens at a glance. It doesn't name a sibling explicitly, so it falls short of full differentiation.

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?

"Pass slug from list_directory_apps" gives clear provenance for the single input, and the Library Pro note flags a prerequisite. However, there is no guidance on when to prefer this over get_directory_screens or get_screenshots, so alternatives are left to inference.

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