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

Annotations provide no hints (all false), so the description carries the burden. It discloses that this is a purchase operation and that sessions are prepaid, and mentions per-query cost and max queries. However, it does not explain side effects (e.g., session creation, wallet deductions), response behavior, or idempotency beyond what annotations imply. It is adequate but not rich.

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 a single, efficient sentence with a concrete example. It is front-loaded with the core purpose and avoids padding. No waste, though it could arguably drop the specific listing example for generality.

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 six optional parameters and no output schema, the description conveys the core action and workflow but omits details like session-handle handling, funding prerequisites, and error cases. The schema covers some parameter semantics, and siblings imply the rest, but a complete description would clarify what 'opening a session' returns and how to reference it later.

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 description makes no mention of any parameters. The schema describes three of six parameters (listing_id, listing_slug, buyer_address) and includes an extensive explanatory note, but the description adds zero parameter-level guidance. With only 50% schema coverage, this is a notable gap.

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 ('Buy per-query access') and a clear resource ('live data listings'), distinguishes itself from the free preview via data_preview, and gives a concrete example listing with pricing. This is unambiguous and differentiates from siblings like data_preview, data_session_fund, and data_session_query.

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?

It explicitly suggests using data_preview for a free taste before buying, and outlines the intended sequence ('Open a prepaid session, then fund and query'). While it does not name specific sibling tools as alternatives, the workflow implication clearly positions this as the opening step, not the funding or querying step.

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