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

Annotations already mark it read-only, idempotent, and non-destructive. The description adds valuable behavior beyond annotations: it requires an API key via Bearer or X-API-Key, is not guest-callable, returns earnings-wallet funding instructions and createEscrow calldata, and exposes the exact REST endpoint. 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?

Three short sentences cover purpose, auth requirements, return value, and REST endpoint without redundancy. The main purpose is front-loaded, and every sentence adds necessary information for invoking the tool.

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, the description covers authentication, session prerequisite, return payload, and endpoint. With no output schema, it still tells the agent what to expect. It also positions the tool in the broader data-session workflow without being verbose.

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 single session_id parameter is already documented as a UUID of a session opened via data_session_open. The description reinforces the context ('for an opened data session') and the endpoint path, but does not need to add much; baseline 3 is appropriate.

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 uses a specific verb ('Buy per-query access') and clearly identifies the resource ('funding package for a data session'). It also distinguishes itself from data_preview by noting the free first taste, and from data_session_fund/attach_escrow by stating it returns instructions and calldata rather than executing funding.

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 context: use it for an opened data session, requires an agent API key, is not guest-callable, and data_preview is the free alternative for a first taste. It does not explicitly enumerate sibling alternatives like data_session_fund or attach_escrow, but the flow is implied well enough.

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