List Available Marketplaces

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

Beyond the annotations, the description adds valuable behavioral context: it never raises ToolError, performs pure introspection, and touches no network. The return format and per-source notes are also disclosed, giving the agent a clear picture of what happens at runtime.

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 well structured and front-loaded: purpose first, then usage timing, then return and error behavior. Each section is concise and every sentence adds useful information without padding.

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 zero-parameter introspection tool, the description is complete: it covers purpose, when to use it, return shape, error behavior, and operational quirks. The presence of an output schema further reinforces completeness.

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 tool has zero parameters and an empty schema, so there is nothing for the description to add semantically. Per the baseline for zero-parameter tools, 4 is appropriate.

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 opens with a specific verb and resource: 'Report which marketplaces this installation can actually query.' It clearly distinguishes this introspection tool from comparison/search tools by stating it reports installation-level capability, not marketplace data.

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 explicitly tells the agent when to call it: 'Call this first when a comparison comes back partial.' It also explains the diagnostic value—distinguishing 'connector isn't installed' from 'marketplace refused us'—but does not name alternative tools or give when-not-to-use guidance.

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