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

The description adds valuable context beyond annotations by indicating a financial action ('Buy', '0.01 USDC/query') and that the platform executes funding on the user's behalf. Combined with annotations (readOnlyHint=false, idempotentHint=true, destructiveHint=false), the agent gets a coherent picture of a state-changing but safe-to-retry operation.

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 two tight sentences, front-loading the primary action immediately. It includes a concrete example listing and ends with the consequence that enables querying. There is no filler, repetition, or unnecessary detail.

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 one-parameter tool with no output schema and simple annotations, the description is mostly complete: it explains the action, the cost model, the workflow predecessor (data_preview), and the follow-on capability (data_session_query). A clear mention of needing an existing session_id is only present in the schema, but the schema fills that gap so the description is adequate.

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?

Schema coverage is 100%: the session_id parameter has a clear description and format. The tool description itself does not mention session_id, so it adds no extra parameter meaning; the schema carries the full burden, making the baseline 3 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 gives a specific verb and resource ('Buy per-query access to live data listings') and even names a concrete listing, so an agent can understand the tool's core function. However, with similarly-named siblings like data_session_funding_package and data_session_attach_escrow, the description does not explicitly distinguish itself from them, so it falls short of full differentiation.

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 gives explicit workflow context: use data_preview for a free first taste and this tool to fund a session before running data_session_query. It does not name every alternative or give exclusion criteria, but the workflow guidance is clear enough for most selection decisions.

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