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

Annotations already indicate readOnlyHint=true, idempotentHint=true, and destructiveHint=false. The description adds useful context by saying it 'Returns fund instructions after data_session_open' and gives pricing, but the opening phrase 'Buy per-query access' is slightly ambiguous against the read-only annotation; it does not clearly state that no funds are moved by this tool itself.

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 the main purpose, followed by the listing, price, and return behavior. The phrase 'first taste free' is slightly informal but still conveys the free preview option without adding meaningful bulk.

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?

With one parameter, annotations, and no output schema, the description gives enough about the return value (fund instructions) and prerequisite (data_session_open). However, it leaves ambiguity about how this tool relates to data_session_fund and whether it actually executes a purchase or only provides instructions, which is important context for correct selection.

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 100%, and the session_id parameter is already well documented as a UUID from data_session_open. The description adds no parameter-level meaning beyond the schema, which is acceptable given the high schema coverage.

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 verb and resource: 'Buy per-query access to live data listings' and identifies the specific listing (scinews) with pricing. It does not explicitly distinguish itself from the closely named sibling data_session_fund, so it loses the top score for sibling differentiation.

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?

Usage context is implied: the tool should be used after data_session_open, and a free alternative is hinted at via data_preview. However, there is no explicit when-not-to-use guidance or comparison against closely related siblings like data_session_fund or data_session_attach_escrow.

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