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

The annotations already provide idempotentHint, destructiveHint, and readOnlyHint, so the description is not required to restate them. It adds valuable behavioral context beyond the annotations: this is a paid transaction ('Buy per-query access', '0.01 USDC/query') and that the platform executes the funding so the session can be queried. It does not over-explain or contradict the 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?

The description is compact and front-loaded with the core purpose. It includes relevant workflow context (preview first, then fund, then query) and pricing in a few sentences. The specific listing name and price add useful operational detail without bloating the description.

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 tool with a complete schema, the description plus schema is enough to invoke the tool correctly. It explains the action, the cost, the prerequisite session_id, and the next step. It does not describe return values, but there is no output schema and the operation is simple enough that this is a minor gap.

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 has 100% description coverage and the only parameter, session_id, is well documented as 'UUID of a data session you opened (from data_session_open).' The tool description adds no further parameter-level meaning, so the baseline of 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 clear verb-resource pair: 'Buy per-query access to live data listings.' It also distinguishes itself from the free preview via 'first taste free via data_preview' and sets up the follow-on action 'so you can data_session_query.' The title 'Fund Data Session (Sandbox)' reinforces the purpose without ambiguity.

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 an explicit workflow: start with data_preview for free, then fund the session, then use data_session_query. It clearly implies when to use this tool (after preview, before paid queries). It does not explicitly mention when not to use it or how it differs from data_session_funding_package, 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.