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

Annotations only declare readOnly and openWorld; the description adds substantial context beyond them: the logged-out surface, the 1-3 post cap, the residential-proxy data path, and the $0.01 USDC x402 pricing model with failed calls not charged. That payment and result-limit detail is decision-critical and unavailable elsewhere.

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?

Two dense sentences, front-loaded with what is returned and followed by sourcing and cost. Nothing is wasted, though the run-on inventory of returned fields is slightly harder to scan than a short structured list.

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?

An output schema exists, yet the description still sets expectations about result truncation, source, and billing — the things an agent must know before committing a paid call. Nothing material is missing for a single-parameter read tool.

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?

A single required parameter with 100% schema description coverage already explains accepted forms (username, numeric id, URL). The description adds no format or edge-case guidance for 'page' beyond the schema, so the baseline applies.

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 resource and scope — 'Latest public posts of a Facebook Page' — and enumerates the returned fields (post id, link, text, time, counts, media type). Clearly separable from siblings like social_facebook_pages or social_facebook_comments.

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?

The 'logged-out visitor' framing plus the note that Facebook only shows the first 1-3 posts tells the agent exactly what results to expect and implicitly when this tool fits versus a fuller scraping route. It stops short of naming an explicit alternative sibling for deeper coverage.

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