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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety profile is covered. The description adds non-obvious behavior: results are a live ranked snapshot at query time (volatility), no silent substitution of hashtag results, and a cost of 1 credit. These are genuine beyond-schema disclosures; only the absence of pagination behavior keeps it from a 5.

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 purpose is front-loaded in the first sentence and each subsequent sentence carries distinct information (index distinction, volatility, cost). Slightly wordy in the 'genuinely different sets' sentence but nothing 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?

No output schema exists, so the description should ideally convey the shape of results and pagination. It covers ranking volatility and that cursor exists, but never explains what a result contains or how to paginate via cursor, and cache_max_age is unexplained. Adequate but with visible gaps for a 3-param 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 coverage is 67%: query and cursor are documented in the schema, cache_max_age is not. The description adds no parameter-level detail beyond what the schema provides, so with partial coverage the baseline of 3 is appropriate.

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+resource ('Search reels by keyword') and distinguishes itself from the hashtag index path. However, it doesn't name sibling tools like instagram_search or instagram_trendingReels, so an agent must infer the boundary against those. Clear purpose but incomplete sibling differentiation.

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?

Implies when to use it via 'Instagram's own keyword search rather than its hashtag index' and 'never quietly substitutes one for the other', giving a real semantic boundary. But it never explicitly says when to pick this over instagram_search, instagram_popularSearch, or instagram_trendingReels. Usage is inferable, not stated.

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