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

Annotations already declare the mutation profile (readOnly=false, idempotent=false, destructive=false), so the description's main contribution is economic behavior: 0.01 USDC per query and a hard cap of 20 queries/session. That pricing/rate-limit detail is genuinely useful and not in the structured fields. It does not, however, explain what happens on an unfunded session or after the cap is hit.

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?

Front-loads the pay-per-query purpose, then the listing/pricing, then the required sequence. No filler sentences. The em-dash-heavy phrasing is slightly dense but every clause carries information.

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 5-parameter, no-output-schema tool with only 40% schema coverage, the description covers the workflow, cost, and cap but leaves three parameters and all return-value expectations unexplained. It is adequate for invoking the tool in the happy path but incomplete for correct parameter usage.

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 only 40%, so the description carries a compensating burden and does not meet it. It never explains k, query, sandbox_receipt, or delivery_receipt, and says nothing about what the query string format should be. The 'max 20 queries/session' note relates to session behavior, not to any parameter.

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 concrete action (run a prepaid per-query lookup against a live listing) and names the specific listing and pricing. It also distinguishes itself from the sibling data_preview ('first taste free'). The verb 'Buy per-query access' is slightly indirect for what is fundamentally a query execution, but the intent is recoverable.

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?

Gives an explicit workflow: data_session_open → data_session_fund → data_session_query, which tells the agent the prerequisites. It also names data_preview as the free alternative to try first. No explicit 'when-not-to-use' or failure guidance, but the routing context is strong.

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