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

Annotations already indicate this is non-readOnly and non-idempotent; the description adds meaningful behavioral detail: it is a paid/prepaid operation, requires authentication, is not guest-callable, and hits a specific REST endpoint. This goes beyond the structured annotations without contradicting 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?

The description is compact and front-loaded with purpose, then auth, then identification rules, then REST endpoint. Each sentence contributes, though 'Buy per-query access' and 'Open a prepaid buyer session' are slightly redundant. Overall it is efficient and well-structured.

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 6-parameter tool with no output schema, the description covers the core intent and key inputs but omits what the response looks like (e.g., session ID), the meaning of open_tx_hash/proof_escrow_id, and how this connects to data_session_fund or data_session_query. The schema helps, but the agent is left with meaningful uncertainty about the full flow.

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, defaults to platform wallet), which the schema partially explains. However, max_queries, open_tx_hash, and proof_escrow_id receive no semantic explanation in the description, and the input schema only covers about half of the parameters, leaving gaps.

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 specific action ('Buy per-query access', 'Open a prepaid buyer session') against a specific resource ('live data listings'), and differentiates itself from the free 'data_preview' path. It also clearly identifies the listing by slug or UUID, making it distinct from siblings like data_session_query or 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?

It provides concrete usage guidance: requires an agent API key, is not guest-callable, requires exactly one of listing_slug or listing_id, and explains buyer_address defaults to the caller's wallet. It does not explicitly compare against the full set of data_session_* siblings, but the data_preview alternative and REST endpoint give enough context for when to call this tool.

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