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

Annotations already declare readOnly/idempotent/non-destructive, and the description adds substantial beyond-schema behavior: billing is per returned row, limit caps both rows and cost, empty results return a `_hint` naming which filter to relax, and returned content is user-generated and should be treated as untrusted. This is exactly the extra context annotations cannot carry.

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-loads the resource and ordering, then filters, then alternatives, then return shape and billing. Every sentence carries operational information; none 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?

With no output schema, the description compensates by enumerating the returned fields (username, follower_count, public_email, etc.), describing the empty-result `_hint`, and warning about untrusted content. Nothing needed to call this correctly 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?

Schema coverage is 100%, so the baseline is 3; the description still adds model-level framing by naming the two filter families, the substring-vs-exact behavior, and the derived-vs-raw nature of meta_category versus category. This is genuinely useful even though the schema already documents each parameter's syntax.

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+scope ('List Instagram business accounts in a category, most-followed first') and explicitly distinguishes itself from both siblings it could be confused with: list_business_categories (for valid labels) and get_top_users (for non-category-bound rankings). An agent can identify this tool without opening the 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?

Gives explicit routing: 'call list_business_categories first for valid labels' and 'use get_top_users for rankings that are not category-bound'. It also names the use case (lead lists with contact details) and explains which of the two mutually-exclusive filters to choose.

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