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

Annotations already indicate mudability (readOnlyHint:false), idempotency, and non-destructiveness. The description adds the behavioral detail that 'platform-executes funding,' meaning the transaction is automated, and provides cost context. No contradiction with annotations; it supplements them adequately.

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 concise sentences, front-loaded with the core purpose, then listing details, then a note on execution. Every sentence earns its place; no redundant or vague phrasing.

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 tool's simplicity (one parameter, no output schema, annotations cover safety), the description is adequate. It covers what, why, and the flow, though it could explicitly mention the prerequisite of an existing session, but the schema already states that. It does not describe edge cases like insufficient funds, but that is not necessary for a basic funding operation.

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 coverage is 100% – the only parameter, session_id, is fully described with 'UUID of a data session you opened (from data_session_open).' The tool description does not add additional semantic meaning beyond what the schema provides, so 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 clearly states the tool's purpose: 'Buy per-query access to live data listings.' It names the specific listing and cost, and mentions the relationship to data_preview (free trial) and data_session_query (post-funding). This distinguishes it from siblings even without opening schemas.

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 implies a workflow: 'first taste free via data_preview' and 'so you can data_session_query,' suggesting you use this after previewing and before querying. It provides clear context but does not explicitly exclude alternatives like data_session_funding_package or attach_escrow, though those are not directly mentioned.

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