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

Annotations already cover read-only, idempotent, and non-destructive behavior. The description adds meaningful context beyond those: per-query billing (0.01 USDC/query), the free preview path, and that the output is fund instructions rather than data or an executed purchase. No contradiction with annotations.

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?

Two sentences that are front-loaded and information-dense. The main purpose appears in the first clause, and every subsequent phrase—free preview, listing, price, return behavior—earns its place with no 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 one-parameter tool with strong annotations, this is mostly adequate, but there is no output schema, so the description carries the burden of explaining what 'fund instructions' contain and how they feed the next step (e.g., data_session_fund). The many similar sibling tools also make the lack of explicit differentiation costlier.

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% and the input schema already defines session_id as 'UUID of a data session you opened (from data_session_open).' The description only repeats the data_session_open prerequisite without adding new parameter-level meaning, so it stays at the baseline 3.

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 action ('Buy per-query access to live data listings'), names the specific listing and price, and notes it returns fund instructions. It distinguishes itself from data_preview and data_session_open, but it does not explicitly contrast with the similarly named data_session_fund sibling, so it is slightly short of a 5.

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?

Provides useful sequencing: 'first taste free via data_preview' and 'Returns fund instructions after data_session_open.' This gives clear context on when in the workflow to use the tool, but it lacks explicit when-not-to-use guidance or alternatives, so it stops 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.