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

Annotations already declare readOnlyHint and openWorldHint, so safety is covered. The description adds genuinely useful context beyond that: the return includes signed CDN URLs and the call costs 3 credits, which is actionable budgeting information an agent cannot infer from structured fields.

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 plus a cost line, front-loaded with the core action. Nothing is padded, though the redundant restatement of 'one highlight' in both sentences is slightly wasteful.

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, the description covers what is returned (photos/videos with CDN URLs) and the credit cost. It omits pagination behavior, item limits, and the id's origin, which are the main gaps an agent would still face.

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 0%; the only hint about the 'id' parameter comes from the schema's example value 'highlight:17960293069066406'. The description does not explain the identifier format, where to obtain it, or that it must be a highlight (not media) id, so it fails to 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?

States a specific verb and resource: 'Get the items in one highlight', and clarifies the payload as 'Every photo and video inside one highlight'. It is clearly distinct from a listing endpoint, though it does not name the sibling instagram_highlights explicitly to contrast 'one highlight' vs 'all highlights'.

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?

No explicit when-to-use guidance. The sibling instagram_highlights (plural) almost certainly lists highlights and would be the prerequisite to obtain the id used here, but the description never says so or explains when to pick this tool over it. Usage is only implied by the word 'one'.

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