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

Adds meaningful behavioral context beyond the annotations: the operation is monetized/prepaid, requires authentication, is not guest-callable, and buyer_address defaults to the caller's platform wallet. The annotations already indicate a mutating, non-idempotent operation, and the description does not contradict them.

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?

Four tight sentences, front-loaded with the core purpose, then auth, selection rule, and REST endpoint. Every sentence contributes a distinct fact, and there is no repetition of schema boilerplate.

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?

Covers the key decision inputs: what the tool does, which listing identifier to provide, auth requirements, and the buyer_address default. However, with no output schema, it does not explain what the response contains (e.g., session id), and it leaves three advanced parameters unexplained, which is a meaningful gap for a state-changing purchase 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?

The description adds important semantics for listing_slug/listing_id (exactly one) and buyer_address (optional, default wallet). However, with only 50% schema coverage, max_queries, open_tx_hash, and proof_escrow_id remain effectively undocumented in both the schema and the description, so the compensation is only partial.

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?

States a specific verb and resource: 'Buy per-query access to live data listings' and 'Open a prepaid buyer session against a public data listing'. It also names the REST endpoint and contrasts itself with the free data_preview, making its role distinct from siblings like data_session_query and data_session_fund.

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?

Explicitly routes the agent to data_preview for a free first taste, establishes the paid/prepaid context, and clearly states auth prerequisites ('Requires an agent API key', 'Not guest-callable'). This gives the agent concrete conditions for when to call this tool versus alternatives.

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