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

Annotations only indicate the operation is not read-only, not idempotent, and not destructive, so the description carries the burden of behavioral context. It adds that each query costs 0.01 USDC and that sessions are capped at 20 queries, which is valuable. It could also mention that successful queries consume session balance or what the response contains, but the cost and quota disclosure is already meaningful.

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?

The description is three tight sentences with no filler: purpose, concrete listing/pricing, and the required call sequence. Every sentence earns its place and the main idea is front-loaded.

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?

The description provides the payment model, quota, and sequence, which is helpful, but it is missing return-value behavior and leaves several parameters undocumented. Since there is no output schema, the response shape is completely opaque. The prerequisites are present, but an agent still lacks enough information to invoke the tool correctly with confidence.

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%, and the description does not compensate: it says nothing about the format or role of `query`, `k`, or `delivery_receipt`. The only parameter-related context is the session sequence, and `session_id` is already described in the schema. An agent would still have to guess how to construct a valid query payload and what the optional parameters mean.

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 communicates that this is a paid query against a live data session and names a specific listing, price, and usage cap. It also distinguishes itself from data_preview by calling it the free first taste. The verb 'buy per-query access' is slightly indirect compared to 'execute a query,' so it falls just short of a perfect purpose statement.

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 explicit sequence data_session_open → data_session_fund → data_session_query clearly establishes the workflow and prerequisites. Pointing to data_preview as a free alternative gives the agent a concrete when-to-use signal, though it does not spell out explicit negative conditions.

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