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

The annotation readOnlyHint is true while the description says 'Buy per-query access' and 'Returns fund instructions'. This is a direct contradiction: buying or funding implies a state-changing financial transaction, not a read-only operation. The description also does not disclose this inconsistency, severely undermining transparency.

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 concise, covering the action, the specific listing, the price, the free preview, and the return type in about two sentences. It is well-structured with no redundant or filler content.

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?

Given the simplicity of the tool (one parameter, no output schema), the description covers essential aspects: what it does, what it costs, what it returns, and the prerequisite session. It lacks only an explicit comparison with the sibling data_session_fund, but is otherwise complete for an agent to 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?

The single parameter session_id has a schema description that fully explains it ('UUID of a data session you opened (from data_session_open)'). This adds useful context over the bare schema, making it clear where the value comes from and that it is required.

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 tool's purpose: buying per-query access to a specific live data listing (RustSec advisories) at a set price, and even mentions the free preview via data_preview. This is a specific verb ('Buy') with a resource and scope, making it easy to distinguish from generic funding tools.

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 implies usage context: it requires an open session (session_id) and mentions data_preview as a free alternative. It does not explicitly differentiate from the sibling tool data_session_fund, but the 'after data_session_open' phrase gives clear sequencing guidance, so it is mostly clear.

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