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

Beyond the readOnly/openWorld annotations the description supplies real behavioral context: the data source (public Page Plugin), the hard 10-Page cap, the notFound error channel for unresolved Pages, and an explicit pricing model ($0.002 USDC via x402 on Base/Solana/Arc) with the important detail that failed calls are not charged. That is exactly the kind of cost and failure-mode disclosure an agent needs before spending money.

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-loaded with the returned fields and scope, then limitations, then price. Every clause is load-bearing — the 'counts only' clause and the per-call price both change how an agent should call it, so density is justified rather than 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 an output schema and annotations already present, the description only needed to cover cost, scope limits, and failure behavior — and it covers all three. An agent can decide whether to call it, how to format input, and what to expect on partial failure without further lookup.

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 single 'pages' parameter is already documented in the schema. The description restates the same accepted formats (username, numeric ID, facebook.com URL) and the up-to-10 limit without adding syntax, delimiter-escaping, or encoding guidance, so it adds little beyond the schema baseline.

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?

The description states a specific verb+resource ('Facebook Page follower counts from Facebook's public Page Plugin') and enumerates exactly what is returned (name, page ID, verified badge, picture URL, exact follower count, sorted by followers). It also rules out the neighbouring concept ('lists of individual followers ... are not returned'), though it never names the close sibling social_facebook_pages, so an agent must still infer the boundary with that tool.

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?

Clear conditions are given: valid for 1 to 10 Pages, counts only, and Pages that can't be resolved land in notFound. The 'when not to use' case (follower/following lists requiring a logged-in session) is stated explicitly, but no alternative sibling tool is recommended for page details, contact info, or other Page attributes.

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