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

Annotations already declare readOnly/openWorld/non-destructive, but the description adds the details annotations cannot: exact billing ($0.008 per page), that cost scales with the pages parameter, and that get_sentiment adds a surcharge. It also discloses that Facebook's ai_label is included in results, which is non-obvious. It does not mention rate limits or any cap on total results beyond the pages parameter.

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, front-loaded with purpose then return contents then options and cost. Every clause carries information an agent would otherwise have to guess at; nothing is padding.

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 seven parameters and no output schema, the description does the necessary work by naming the returned fields (text, author, engagement, media, ai_label) and the cost model. Minor gaps remain — how pagination behaves past the 15-page cap and whether the query supports operators or phrase syntax are unstated.

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 every parameter is already documented with defaults, enums, and formats. The description restates the date-range, sort, and location_id semantics without adding syntax the schema lacks, so the schema is doing the heavy lifting and a baseline 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 and resource ("Search public Facebook posts by keyword") and immediately distinguishes itself from page-scoped or group-scoped siblings by specifying "public" keyword search. The second sentence enumerates what comes back, so an agent knows the payload shape 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?

Gives clear selection levers — date range, sort order, and location scoping via a location_id obtained from search_facebook_locations — which is genuine routing guidance. It stops short of explicitly excluding the page/group post siblings (facebook_page_posts, facebook_group_posts), so the agent must infer that this tool is the cross-account keyword search rather than a per-entity feed.

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