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

Annotations only provide readOnlyHint and openWorldHint, so the description carries the interesting constraints and does so well: only the initial server-rendered page is returned, further pagination requires login and is unsupported, and retries can take roughly a minute. These are exactly the operational facts an agent would otherwise discover by failing.

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 purpose and return contents, then constraint by constraint with no filler sentences. It is clause-dense and would read better as a short list, but nothing is redundant enough to cut.

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?

For an 8-parameter, read-only, open-world scrape with an output schema, this covers the remaining gaps: pagination ceiling, auth requirement, filter prerequisites, category exception, latency, and the sibling handoff. Nothing an agent needs before calling 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 description coverage is 100%, so the per-parameter meanings are already documented, and the description largely restates the same 'requires query or category' rule. It does add one genuinely new detail the schema lacks: property_rentals bypasses those filter prerequisites in favor of its own filtered page.

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?

Opens with a specific verb and resource ('Fetch public Facebook Marketplace listing rows for a location') and names exactly what is returned (titles, prices, thumbnails). It also distinguishes itself from the sibling facebook_page explicitly, so an agent can route without opening any 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 when-to-use conditions: omit query and category for a browse feed, filters require query or category, property_rentals uses its own filtered page, and use facebook_page for page profiles. Alternatives and their selection conditions are stated rather than implied.

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