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

The description goes beyond annotations by clarifying the tool returns fund instructions and must be used after data_session_open. The readOnlyHint and idempotentHint are consistent with 'Returns fund instructions' rather than executing a financial mutation, so there is no contradiction.

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: it states the core purpose, points to the free preview, gives the specific listing and price, and notes sequencing and return behavior. Every sentence contributes useful information with no repetition.

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 no output schema, the description is mostly sufficient for selection and invocation, but it leaves the exact nature of the 'fund instructions' vague and does not explain how they connect to sibling tools like data_session_attach_escrow or data_session_fund. This is a meaningful gap for workflow planning.

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 fully documents the single session_id parameter, and its description explains it comes from data_session_open. With schema description coverage at 100%, the tool description adds little parameter-level meaning, so a baseline score of 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 states a clear action ('Buy per-query access to live data listings') and gives a concrete listing with price, so the agent can see what this tool is for. It also distinguishes itself from data_preview by offering a free alternative, but it does not explicitly distinguish itself from closely related siblings like data_session_fund or data_session_attach_escrow.

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?

It gives useful sequencing information: 'Returns fund instructions after data_session_open' and points users to data_preview for a free first taste. This provides clear context and an explicit alternative for the free path, though it does not say when to use this tool versus data_session_fund or data_session_attach_escrow.

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