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

With no annotations provided, the description carries the full burden of behavioral disclosure. 'Fetch' implies a read-only retrieval, but the description does not disclose error behavior, return format, authentication requirements, rate limits, or any side effects. This is a minimal statement with no depth beyond the core action.

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 one concise, front-loaded sentence ('Fetch one listing by its source_url.') with no redundant words. Every term earns its place, making it an exemplary concise structure.

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?

The tool has no output schema and no annotations, so the description should explain what a successful result looks like and how failures surface. It only states the input and a vague output ('one listing'), leaving an agent without enough context to handle missing records, response shapes, or when this tool is preferable to sibling tools.

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 schema has zero description coverage for the source_url parameter, but the tool description says 'by its source_url,' which clarifies that source_url is the unique identifier used to select the listing. This adds meaningful semantics beyond the raw schema and fully compensates for the single parameter's lack of description.

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 states a specific verb ('Fetch') and resource ('one listing') plus the identifying key ('source_url'), making the tool's purpose clear. It does not explicitly distinguish itself from siblings like coverage or search_stock, but the phrasing narrows the action to a single-record lookup.

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?

No guidance is given about when to use this tool versus the alternatives (coverage, search_stock). The only implied use case is 'when you have a source_url and need one listing,' but no explicit conditions, exclusions, or alternative routing are provided.

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