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

Annotations already indicate this is a non-read-only, non-idempotent, non-destructive operation; the description adds valuable context on top: each call costs 0.01 USDC, is capped at 20 queries/session, and requires prior open+fund steps. Failure/refund behavior and receipt-signing side effects are not disclosed, but the costly-and-metered nature is clearly conveyed.

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?

Three tight sentences, each earning its place: the core action, the pricing/limits, and the required calling sequence. The most decision-relevant facts (paid, preview alternative, prerequisites) are front-loaded with zero filler.

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 tool with no output schema, the description covers the commercial model and prerequisite flow well, but leaves gaps: parameter semantics for k/delivery_receipt, what the response contains, and behavior on failed or unfunded queries. Adequate for the happy path, incomplete for a new agent that must invoke it correctly.

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 tool description carries the burden of explaining the undocumented parameters (query, k, delivery_receipt). It does not: nothing explains what the query string should contain, what k controls (result count), or what delivery_receipt/sandbox_receipt mean functionally. The only parameter-related hint is the word 'query' in the name and sequence.

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 states a specific action ('Buy per-query access to live data listings') and is reinforced by the schema description 'Run a prepaid query against a funded data session.' It names the exact listing, price, and per-session limit, and explicitly distinguishes itself from the free data_preview sibling and the data_session_open/data_session_fund steps in the sequence.

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 clear when-to-use context: use data_preview for the free first taste, then follow the explicit sequence data_session_open → data_session_fund → data_session_query. It does not exhaustively state when not to use the tool or name alternative tools for edge cases (e.g., unfunded session recovery), so it falls just 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.