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

The annotations already communicate non-read-only and idempotent behavior. The description adds meaningful financial context beyond annotations: this tool 'platform-executes funding,' implies a paid transaction, and discloses the per-query price. It does not detail balance, refund, or failure behavior, but it provides the most important behavioral trait for an agent: money movement that enables subsequent queries.

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 short and front-loaded with the core action, then references data_preview and data_session_query to give quick orientation. The 'Listing: RiverWatch' detail is concrete but slightly tangential, and the promotional 'first taste free' phrasing is not strictly necessary; still, the overall length is appropriate and nothing important is buried.

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?

The tool has one required parameter, no output schema, and is a financial mutation. The description explains the purpose and workflow adequately for a simple call, but it does not describe what the function returns, how success is signaled, or what happens to the session after funding. It also leaves the relationship to data_session_funding_package ambiguous, which is a meaningful gap given the sibling set.

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 input schema already covers the only parameter, session_id, with 100% description coverage. The tool description adds no new parameter-level meaning, such as how session_id is obtained or validated, beyond what the schema already states. Baseline 3 is appropriate because the schema carries the semantic load.

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 action ('Buy per-query access to live data listings') and connects it to downstream use via data_session_query. It also positions data_preview as the free first step, which helps distinguish it from one sibling. However, it does not explicitly differentiate itself from data_session_funding_package, so the purpose is clear but not fully discriminative among the sibling 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 gives useful workflow context: try data_preview first for free, then use this tool to fund, then call data_session_query. This implies the intended sequence and relationship to siblings. It stops short of stating when not to use this tool or when to prefer data_session_funding_package instead, so it lacks explicit exclusions.

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