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

Annotations already declare readOnlyHint=true and idempotentHint=true, lowering the bar. The description adds the pricing model, the fact that it returns instructions, and the dependency on an opened session. However, the verb 'Buy' could misleadingly imply a side effect, and the description never explicitly says no payment is executed.

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 convey the action, exact listing, price, free-preview alternative, precondition, and return behavior with no filler. The concrete example is useful and 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 read-only annotations and no output schema, the description adequately covers when to call it and what it returns. The main gap is that 'fund instructions' are not detailed enough to tell the agent whether to display them or pass them to a sibling like data_session_fund.

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 single session_id parameter is fully documented by the input schema (100% coverage), so the schema carries the semantic weight. The description's 'after data_session_open' aligns with that parameter, but it adds no new detail about format, source, or constraints beyond what the schema already 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 clearly states the action as 'Buy per-query access to live data listings' and identifies the exact listing and price (quantawatch, 0.01 USDC/query), while noting the return is fund instructions. It is specific about the resource, but it does not explicitly differentiate itself from sibling tools like data_session_fund 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 gives concrete workflow context: call it after data_session_open, and points to data_preview as the free first taste. It does not, however, explicitly state when not to use this tool or name alternatives for the actual funding step, so it stops short of a 5.

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