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

Annotations already declare readOnlyHint=true and openWorldHint=false, so the safety profile is covered. The description adds that results are ranked and that ranking is selectable, but it doesn't disclose edge-case behavior such as what happens for private or unknown accounts, or whether post-level metrics accompany each result.

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 sentences with zero filler: the capability and its ranking axes come first, then the usage triggers. Nothing is redundant with the title or schema.

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?

All four params are documented and annotations cover the read-only nature, so an agent can call this correctly. With no output schema, a brief hint about what each returned post contains would have closed the last gap.

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%, so all four parameters (username, limit, period, sort_by) are already fully documented with enums, defaults, and bounds. The description echoes the sort criteria but adds no syntax, default, or interpretation detail beyond the schema — baseline 3.

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 (get), resource (top performing Instagram posts for an account), and the ranking dimensions used. It also implicitly disambiguates from siblings by naming the platform and the 'top posts' concept, distinguishing it from get_post_insights or the TikTok variant get_tiktok_top_videos.

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?

The second sentence gives explicit intake triggers — 'best posts', 'top content', 'viral posts', 'highest performing content' — which maps cleanly to user phrasing. It stops short of naming alternatives or when-not-to-use cases (e.g., single-post analysis belongs to get_post_insights).

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