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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), and the description adds information they cannot carry: the 404-before-first-refresh behavior and the zeros-not-errors degradation for small accounts. Those are exactly the failure modes an agent needs to interpret a bad-looking response correctly.

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 core statement, then the data availability caveats, then the use case. Mostly tight, but 'followers online by hour' is stated twice (mid-description and again in the closing sentence), which is a small redundancy.

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 parameters, no output schema, and no nested objects, the description carries the full explanatory load and does so: it describes the return shape field by field and covers both empty-state conditions. Nothing needed to interpret a successful or failing call is missing.

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?

The tool takes zero parameters, so there is no parameter semantics to explain and the baseline of 4 applies. The description correctly spends its budget on return content and edge cases instead.

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 audience demographics') and immediately enumerates the breakdown: gender/age percentages, top countries and cities, followers online by hour. That content profile implicitly separates it from a generic sibling like get_account_insights, though no sibling is named explicitly.

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 real operating context: 404 until the first refresh, and Instagram withholding data for accounts under ~100 followers. It also names the downstream question this answers ('when should I post'). It stops short of explicitly routing to or away from alternatives such as get_account_insights or get_follower_history.

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