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

The key behavioral claim is that this tool does not itself perform a charge; it 'Returns fund instructions,' aligning with the readOnlyHint and idempotentHint annotations by implying no state change or purchase execution. It also exposes workflow order and the listing price. It does not discuss auth or rate limits, but the annotations already cover the safety profile.

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?

Two sentences pack in the purpose, the free-preview alternative, the specific listing, the price, and the return behavior with little redundancy. The wording is compact, though the promotional tone and ambiguous 'fund instructions' keep it from being maximally crisp.

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 rich annotations and complete schema coverage, the description covers the workflow and purpose adequately. But 'Returns fund instructions' is vague without an output schema, and the description never clarifies what a funding package does versus the data_session_fund sibling, leaving the agent to infer part of the contract.

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 only parameter, session_id, is already fully documented in the schema with its source (data_session_open). The description reinforces the 'after data_session_open' sequencing but adds no new formatting, constraints, or value semantics beyond what the schema provides.

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 names a specific action—'Buy per-query access to live data listings'—and identifies the exact listing and price, so an agent knows what resource is involved. It also ties the tool to data_session_open's workflow. However, it does not clearly differentiate this from the sibling data_session_fund, which could plausibly be the actual purchase action.

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 points to data_preview for the free 'first taste' and states that the tool returns fund instructions after data_session_open, giving clear contextual sequencing. It does not say when to prefer this tool over data_session_fund or data_session_attach_escrow, so no true exclusion list is provided.

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