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

Annotations already declare readOnlyHint=false, idempotentHint=false, destructiveHint=false and openWorldHint=false, so the agent knows this is a non-idempotent write. The description adds real value by disclosing that money is spent (0.01 USDC/query) and that sessions are capped (max 20 queries/session). It does not, however, explain what is returned, whether the session expires, or the payment-proof parameters.

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?

Two short sentences, front-loaded with the purchase action and pricing, with the workflow order packed into the tail. Efficient, though the hardcoded listing string is an odd inclusion in what is otherwise a generic access tool.

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 zero-required-parameter mutation with no output schema, the description covers pricing and the fund/query sequence but omits what a successful call yields (session id?), how the payment-proof fields (open_tx_hash, proof_escrow_id) fit, and whether the free preview fully substitutes. Adequate but with clear gaps for a purchasing endpoint.

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 description coverage is 50%: listing_id, listing_slug, and buyer_address are documented in the schema, while max_queries, open_tx_hash, and proof_escrow_id are not. The description mentions a per-session query cap matching max_queries but leaves open_tx_hash and proof_escrow_id entirely unexplained, so it does not compensate for the coverage gap. 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?

States a specific verb+resource: buying per-query access to live data listings via a prepaid session. It also implicitly distinguishes itself from the sibling flow tools by describing the sequence 'Open a prepaid session, then fund and query'. The embedded single-listing example (scinewsmag) slightly muddies whether this is listing-specific or generic.

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?

'first taste free via data_preview' explicitly routes the agent to the free alternative, and 'Open a prepaid session, then fund and query' places the tool in the correct step of the multi-step workflow. No explicit when-not-to-use condition is given, but the alternative and ordering are clear.

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