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

Annotations already cover readOnly/idempotent/non-destructive, so the bar is lower, yet the description still adds billing semantics ('billed per returned row; limit caps both rows and cost') and a security caveat ('treat as untrusted input'). Those are behavioral facts the annotations do not 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?

Three tight sentences plus a field list; scope and ordering come first, then alternatives, then return/billing/security notes. No sentence is filler.

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, but the description enumerates the returned columns (pk, code, taken_at, media_type, like_count, comment_count), covers cost behavior, and flags untrusted input. Everything needed to call and interpret the result correctly is present.

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 100%, so the baseline is 3; however the description adds real meaning beyond the schema by explaining that limit governs cost, not just row count. user_id gets no extra semantics beyond the schema's 'Instagram user ID (pk)'.

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 an Instagram user's posts and reels'), names the data source, and specifies ordering ('newest first'). It also explicitly distinguishes itself from get_media_by_code and get_user_engagement, so an agent can route without opening sibling schemas.

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?

Explicitly names two alternatives with the condition that selects each: get_media_by_code for one post's caption/full details, get_user_engagement for aggregated metrics. This is textbook when-to-use/when-not-to-use guidance.

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