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

Annotations show this is a mutating operation (readOnlyHint=false) but leave most behavioral context uncovered. The description adds useful context about paid per-query access, the 0.01 USDC/query cost, a max-20-queries-per-session note, and the open-then-fund-then-query workflow. It does not disclose session-creation side effects, payment prerequisites, what a successful open returns, or why open_tx_hash and proof_escrow_id exist, but it does not contradict the annotations.

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 and front-loaded with the core purpose and workflow. The specific 'scibreak' listing example and pricing add color but are not generic tool behavior, so they are slightly less relevant than a more abstract statement would be; still, there is very little wasted text.

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?

This is a payment-related state-changing tool with five parameters and no output schema, so the description needs to explain required inputs, optional fields, and expected outcomes. It provides a high-level buying workflow but omits what values to pass, what the session open produces, and how the escrow/transaction fields fit in. That is a material gap for an agent attempting to invoke the tool correctly.

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 0%, so the description must compensate, but it never explicitly explains the five parameters. 'Listing' and 'max 20 queries/session' weakly hint at listing_id and possibly max_queries, while buyer_address, open_tx_hash, and proof_escrow_id are left unexplained. With no parameter-level guidance, an agent cannot reliably construct a valid call beyond maybe guessing the listing id.

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 action ('Buy per-query access' and 'Open a prepaid session') and the resource (a data session for a listing). It distinguishes itself from the sibling data_preview by saying the first taste is free there, and the phrase 'then fund and query' marks this as the session-opening step rather than a query or funding step.

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 gives a clear usage context: use data_preview for the free taste, then open a prepaid session, then fund and query. It thus implies when this tool should be used relative to siblings. However, it does not explicitly name data_session_fund or data_session_query as the alternatives for the later steps, nor does it state explicit when-not-to-use conditions beyond the preview case.

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