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

Annotations already declare idempotentHint=true and destructiveHint=false, covering the safety profile. The description adds useful behavioral context: this is a paid operation at 0.01 USDC/query and funding is platform-executed. It does not explain more about balance effects or confirmation behavior, but the annotation coverage lowers the burden.

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 short and front-loaded with the core action and cost, then references the related tools. The specific listing detail is slightly promotional but still relevant. Every sentence earns its place, and there is no filler.

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 single-parameter tool with full schema coverage and annotations, the description provides enough context to call it: it names the upstream preview step and the downstream query step. The main gap is not explaining how it differs from the other funding-related sibling tools, which is a moderate completeness issue.

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 fully documents the only parameter, session_id, and its description already points back to data_session_open. The tool description adds no additional meaning about how to fill in session_id, so the baseline of 3 applies.

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 uses a specific action ('Buy per-query access') tied to a concrete resource (a data session) and names the exact listing and price. It distinguishes itself from data_preview and data_session_query by placing it between them in the workflow, though it does not explicitly differentiate from sibling funding tools like data_session_funding_package or data_session_attach_escrow.

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 a clear workflow: try the free data_preview, then fund the session, then use data_session_query. However, it gives no explicit guidance about when to choose this tool over the closely related data_session_funding_package or data_session_attach_escrow, so an agent may struggle to select among the funding siblings.

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