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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false. The description adds output behavior ('Returns fund instructions') and pricing (0.01 USDC/query), which is useful given no output schema, but the marketing verb 'Buy' sits in mild tension with readOnlyHint — though the 'returns fund instructions' clause clarifies no purchase is executed here.

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?

Reasonably short and front-loads the core purpose, but mixes pricing, a specific listing name, and workflow notes into a single run-on that reads as partly listing boilerplate rather than agent-directed guidance.

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?

No output schema exists, so the description's note that it returns fund instructions partially compensates, and annotations cover safety. Still thin for a payment-adjacent tool: it omits what the funding instructions contain and what step follows.

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 description coverage is 100% with the single session_id fully documented as a UUID from data_session_open. The description adds no parameter detail, so the baseline 3 applies since the schema does the heavy lifting.

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?

States a specific action and resource ('Buy per-query access to live data listings') and names related tools (data_preview, data_session_open). However it muddles purpose with listing boilerplate and does not clearly distinguish itself from close siblings 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?

Implies a workflow ('first taste free via data_preview', 'Returns fund instructions after data_session_open'), which hints at when to preview versus fund. But it never states when to choose this over the near-identical data_session_fund / data_session_attach_escrow siblings.

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