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

Annotations only cover the readOnly/openWorld safety profile, so the description usefully adds that responses carry signed CDN URLs and, notably, the credit-cost model with per-account caching semantics. It stops short of describing pagination or item limits, but the billing behavior is genuinely value-adding beyond 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?

The core action is front-loaded in the first sentence, with a short elaboration on payload, then the cost note. Slight redundancy between the opening sentence and the 'Every photo and video' clause, but nothing is wasted overall.

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 compensates by stating the return payload (photos/videos with signed CDN URLs) and the cost model. For a single-parameter read tool this is nearly complete, missing only pagination or volume expectations.

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% and the id parameter is fully documented there, including the optional 'highlight:' prefix and source endpoint. The description adds no parameter-level detail, so the baseline 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 the items in one highlight') and elaborates that the contents are photos and videos. It implies a distinction from the plural sibling instagram_highlights but never names or explicitly contrasts with it, leaving the boundary to inference.

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, when-not, or named alternative is given; the agent must infer this is the drill-down after instagram_highlights. The billing note ('first time for an account; more free for 15 minutes') is practical context but describes cost, not selection guidance.

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