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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint. The description usefully adds that the tool returns fund instructions rather than performing the payment, and it specifies the exact listing and price. This adds meaningful behavioral context beyond the structured hints.

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 deliver the action, prerequisite, free alternative, exact listing, price, and return behavior. There is no filler or redundant repetition of the schema or annotations. Every clause earns its place.

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 no output schema, the description is nearly complete: it explains what the tool does, when to use it, what it returns, and the prerequisite. It could be slightly stronger by naming the next step after receiving fund instructions, but that does not impair correct invocation.

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 input schema has 100% description coverage for the single session_id parameter, already explaining it must come from data_session_open. The tool description reinforces this by mentioning 'after data_session_open', but it does not add substantial new parameter-level information beyond the schema.

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 clearly states a specific action and resource: 'Buy per-query access to live data listings', with a concrete listing, price, and free-preview alternative. It distinguishes itself from data_preview and implies a sequence with data_session_open. This is more than enough for an agent to identify the tool's purpose.

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 says to use this after data_session_open and mentions data_preview as the free alternative. It does not explicitly contrast with data_session_fund or data_session_attach_escrow, but the prerequisite and alternative guidance give clear usage context.

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