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

Beyond the annotations (readOnlyHint, openWorldHint), the description discloses meaningful behavior: results are limited to what Facebook shows logged-out visitors, and without an API key each successful call costs $0.05 USDC via x402 on Base or Solana. That cost/auth context is genuinely useful; only failure/not-found behavior and rate limits are unaddressed.

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?

Purpose and identifier forms are front-loaded, followed by the returned fields and payment note. The single sentence with a long parenthetical is dense but largely earned; it stays within reasonable length.

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, so the description carries the return-value burden and does so by listing the fields available. Combined with the visibility scope and payment terms, an agent has enough to call it correctly; only missing-result handling and quota details are absent.

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?

With one parameter at 100% schema coverage, the schema already documents the accepted identifier formats, so the baseline is 3. The description adds only the notion that the identifier may refer to a Page or a person, which is marginal.

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 — fetching 'The public Facebook profile for a Page or person' — and enumerates the fields returned (name, IDs, verified badge, follower counts, About section). It implies differentiation from the sibling facebook_name_search by accepting 'username, numeric ID or link' rather than a name, though it never names that alternative.

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?

Usage is only implied: the identifier forms (username, numeric ID, link) suggest when this lookup is the right choice over a name search, but no explicit when-to-use or when-not-to-use guidance and no named alternative are given.

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