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

Annotations already cover read-only and open-world behavior, so the bar is lower; the description adds real value beyond them by disclosing the return fields and a concrete cost ('3 credits'). It stops short of noting rate limits or behavior on empty/private profiles.

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, lead sentence first, return shape second, follow-up third, cost last. Nothing is padded and no sentence is redundant.

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 usefully names what each highlight contains and the cost, which is what an agent needs to plan a call. It is slightly thin on edge cases (users with no highlights, private accounts) but adequate for a two-optional-param read tool.

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 both parameters are fully documented with examples, so the baseline is 3. The description's 'Pass an id' sentence refers to the other endpoint's highlight id, not to this tool's user_id/username, so it adds no new parameter meaning here.

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 Instagram story highlights') and then specifies the returned shape (title, cover image, item count). It also routes to the singular sibling instagram_highlight for per-highlight items, so an agent can distinguish the two without opening a 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?

Gives an explicit follow-up path: 'Pass an id to /v1/highlight for its items,' which tells the agent when to switch tools. It does not, however, contrast this with sibling listings like instagram_stories or state any precondition (e.g. private accounts).

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