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

Annotations only provide non-read-only, non-idempotent, non-destructive hints, so they do not disclose safety or mutation details. The description adds that this is a paid, prepaid, per-query access with a 20-query session cap, which is useful, but it does not explain what 'open' creates, whether a blockchain transaction is involved, what errors may occur, or what the caller receives in return.

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 short, front-loaded with the core action, and avoids fluff. The specific example listing is concrete but slightly narrow; still, it does not obscure the tool's purpose. The schema-level description is verbose, but that is technical rationale rather than the main tool description.

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?

The description conveys the payment model, session limit, and high-level lifecycle (preview, open, fund, query). Given six parameters, no output schema, and a mutating payment-related operation, it omits useful details such as required preconditions, what a successful open returns, and how funding/escrow parameters relate to the session.

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 only 50%, so the description must compensate. The top-level description adds context about the listing, cost, and session query limit, and the schema-level description explains listing_id/listing_slug exclusivity and buyer_address defaulting. However, max_queries, open_tx_hash, and proof_escrow_id still lack meaningful semantic explanation beyond their names and constraints.

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, specific action: buy per-query access to live data listings by opening a prepaid session. It also names the free preview alternative, data_preview, and gives concrete listing/cost context, so an agent can distinguish this tool from the preview tool without inspecting 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?

It gives useful workflow guidance: try the free preview first via data_preview, then open a prepaid session, then fund and query. It does not explicitly state when not to use data_session_open versus data_session_fund/query, but the staged workflow makes the intended sequence reasonably clear.

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