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

Beyond the readOnlyHint/openWorldHint annotations, the description discloses the return payload (every photo and video, with signed CDN URLs) and a non-obvious cost model: 3 credits the first time per account, with other highlights of the same account free for 15 minutes. That billing/caching behavior is exactly the kind of trait annotations cannot convey.

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?

Front-loaded with the purpose, which is good, but the cost is stated twice ('Costs 3 credits the first time...' then 'Cost: 3 credits.'), and the second mention is pure redundancy. Trimming it would tighten the definition without losing 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, the description supplies the essential missing pieces: what is returned (media with signed CDN URLs) and the credit cost. Only the identifier format and any failure modes are left unaddressed, which is a minor gap given an example exists in the schema.

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?

One parameter at 0% schema description coverage. The description only implies the id is a highlight identifier via 'one highlight'; it does not state the required format, while the schema covers that solely through an example value ('highlight:17960293069066406'). Marginal value added.

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?

Clear verb + resource: 'Get the items in one highlight,' and the singular 'one highlight' implicitly contrasts with the sibling instagram_highlights which presumably lists highlights rather than their contents. It never explicitly names that sibling, so the distinction is left 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?

Usage is implied by the noun phrase (fetch contents of a single highlight), and the credit/caching note hints at a cost consideration before calling. However, it gives no explicit when-to-use-vs-instagram_highlights guidance and no prerequisites or exclusions.

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