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

With no annotations provided, the description carries the full burden and discloses meaningful operational behavior: the exact credit cost, that empty results and failures are not charged, and that cache=true provides a free 24h cache hit. It does not explicitly state read-only semantics or rate limits, but the billing and caching details are unusually specific and valuable.

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?

The description is compact and front-loads the resource and key fields before moving to cost and caching details. The phrase 'coords (2 credits)' is slightly cryptic, but the overall structure is efficient and each sentence contributes useful information.

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 a simple two-parameter tool with no output schema, the description lists the expected return fields and covers billing, failure charging, and cache behavior. It could be more explicit about URL input and error details, but the schema covers the URL and the description mentions failures.

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?

The input schema already provides 100% parameter coverage, including URL platform matching and cache behavior. The description mostly reiterates the cache parameter and cost, adding no new semantic meaning beyond what the schema already documents.

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 identifies a Marketplace listing and enumerates its returned fields (title, priceAmount, status, seller, condition, coords), making it clear this is an item-detail endpoint. It lacks an explicit verb like 'fetch' or 'get', but the resource scope is unambiguous and distinguishable from the marketplace search siblings.

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 description implies usage with a specific Marketplace item URL and touches on cache usage, but it never explicitly contrasts this tool with facebook_marketplace_search or facebook_marketplace_location_search. The intended use case is inferable from the required URL and the term 'Marketplace listing', but no direct guidance is given.

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