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 genuinely new behavior: per-row billing, that `limit` caps both rows and cost, the exact return fields, and that results are untrusted user-generated content. These are operational facts an agent cannot get from structured fields.

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?

Four sentences, zero filler: purpose and ordering first, then routing alternatives, then return/billing semantics, then the trust warning. Each sentence carries distinct, load-bearing information.

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 compensates by enumerating the returned columns (pk, text, commented_at, like_count) along with billing and ordering. Combined with annotations covering safety, an agent has everything needed to call this correctly.

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. The description earns above baseline by clarifying that 'text' means case-insensitive substring matching and, importantly, that `limit` is a cost control as well as a row cap — meaning the schema alone does not convey.

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 Instagram comments'), the scope ('across all users'), the match semantics ('case-insensitive substring match') and ordering ('newest first'). It also explicitly names the two sibling tools it is not, so an agent can route 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?

'Use it for brand or keyword mentions' gives the positive condition, and it names two explicit alternatives with their selecting conditions: `get_comments_by_user` for a single author and `search_media_captions` for post captions. Nothing is left to inference.

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