List Available Marketplaces

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

Annotations already declare readOnlyHint, idempotentHint, etc., but the description adds substantial behavioral context beyond that: it never raises ToolError, performs pure introspection, touches no network, and documents the return format including server metadata and per-source notes. This gives the agent a full picture of what the tool does and what to expect.

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 with clear headings for purpose, return format, and error format. Every sentence provides useful information — no filler. The use of bullet-like examples and plain object field listing keeps it compact while being fully informative.

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 tool with no parameters, an output schema, and a clear diagnostic role, the description is complete. It explains return format, error behavior, and usage context. There are no missing pieces that would leave an agent uncertain about invocation or interpretation of results.

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, so there is no parameter semantics to clarify. Per the baseline, a 0-parameter tool with full schema coverage earns a 4; the description adds value by explaining the return structure, which compensates for the lack of parameters.

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 'Report which marketplaces this installation can actually query' — a specific verb and resource that clearly states the tool's function. It also distinguishes this from sibling marketplace tools by framing it as a diagnostic first call for partial comparison results, which uniquely positions it among the sibling list.

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 states when to use it: 'Call this first when a comparison comes back partial' and explains the key distinction between 'connector isn't installed' and 'marketplace refused us', which require different fixes. This directly answers when and why to use this tool versus alternatives.

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