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

Beyond the readOnlyHint/openWorldHint annotations, the description discloses the access path (residential proxy), a hard result ceiling (~15-25 listings), the billing model ($0.01 USDC per successful call via x402 on Base/Solana/Arc), and that failed calls are free. The one gap is that it doesn't say whether the shallow cap can be exceeded or what an empty result means, which is notable for a paid-per-call tool.

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 is front-loaded and the second sentence cleanly handles cost and access. The long comma-separated field enumeration is somewhat redundant given an output schema exists, but it is compact and skimmable rather than wasteful.

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 present and 100% parameter coverage, the description only needs to add scope, access method, and cost — and it covers all three, including the important caveat that results are a shallow non-authenticated sample. Nothing an agent needs to decide or call correctly 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% — city slug format, query examples, and min/max price are all documented in the schema — so the description adds nothing parameter-level beyond restating 'search for a city'. Baseline 3 is appropriate when the schema does the heavy lifting.

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 — 'Facebook Marketplace search for a city' — and immediately bounds it with '(logged-out view, the first ~15-25 listings)', which separates it from the sibling social_facebook_search and other social_facebook_* tools without needing the schema. It also enumerates the returned fields, so an agent knows exactly what it gets.

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 view, ~15-25 listings' parenthetical implies when this tool is appropriate (shallow, unauthenticated listing lookups) but never states when not to use it or names an alternative such as social_facebook_search or social_olx. Usage is inferable rather than spelled out.

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