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

Annotations already declare the operation read-only and idempotent. The description adds useful behavioral context: it returns fund instructions rather than executing a purchase, and it requires an existing opened session. The word 'Buy' could imply a side effect, but 'Returns fund instructions' reconciles this with the read-only annotation.

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 with no filler. The core action is front-loaded, and the price, prerequisite, and free alternative are compactly included.

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 single-parameter, read-only tool with good annotations and full schema coverage, the description covers purpose, prerequisite, return behavior, and cost. It is slightly vague about the content or format of the returned fund instructions, but it provides enough for an agent to invoke the tool 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 coverage is 100%, and the only parameter session_id is already described as the UUID from data_session_open. The description reinforces the prerequisite but does not add any new parameter-level meaning, so the baseline 3 applies.

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') and a specific resource (the scibreak listing with price). It also distinguishes itself from data_preview by calling it the free first taste, making the tool's purpose clear relative to siblings.

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 clearly places the tool in a workflow: use data_preview first for free access, and call this after data_session_open. It does not explicitly enumerate exclusions for other funding-related siblings, but the main usage context is evident.

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