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

Annotations already indicate this is a non-read-only, idempotent, non-destructive operation. The description adds valuable behavior context: payment is per-query, the platform executes the funding, and the exact cost is disclosed. It does not detail session-state changes or cancellation behavior, but with annotations covering the main safety profile, this is sufficient.

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 compact and front-loaded, opening with the core action before giving price and workflow context. The specific listing and price are useful but arguably narrower than the generic tool name; overall, every sentence earns its place.

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 single parameter is fully described by the schema, and annotations cover idempotence and non-destructiveness, the description fills in the remaining operational context: cost, platform-executed funding, and the downstream query capability. It could have explicitly mentioned opening a session first via data_session_open, but the schema already covers that prerequisite.

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?

There is only one parameter, session_id, and the schema already fully describes it as a UUID from data_session_open. With 100% schema description coverage, the baseline is 3, and the description does not add meaningful parameter detail beyond the schema.

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 identifies the action ('Buy per-query access'), the resource ('live data listings', specifically the pypiwatch listing), and the price. It also distinguishes itself from data_preview by positioning preview as free and from data_session_query by describing funding as the step that enables querying. It stops short of naming close siblings like data_session_funding_package or data_session_attach_escrow, so differentiation is strong but not complete.

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 a clear usage pathway: try data_preview first for a free taste, then fund the session, then call data_session_query. This is useful when-to-use guidance relative to the main workflow. However, it does not explicitly exclude or compare against sibling funding-related tools, so it lacks explicit when-not-to-use guidance.

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