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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false, and the description is consistent with that: it says the tool returns fund instructions rather than charging, so the seemingly transactional 'Buy' framing is not a contradiction. It adds useful context beyond annotations — pricing model, the free preview path, and the required session prerequisite — though it doesn't say whether sessions expire or what the fund instructions contain.

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?

Three short sentences, front-loaded with the value proposition, then the concrete listing and price, then the return behavior. The 'Listing: statwatch: STAT News...' clause is dense but carries real information; no filler.

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?

There is no output schema, and the description compensates by stating what comes back ('Returns fund instructions') along with the prerequisite and the pricing. For a single-parameter read-only tool this covers what an agent needs, with only minor gaps around session lifetime and downstream steps left implicit.

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?

Only one parameter and schema description coverage is 100%, so the schema already fully explains session_id including its format and origin (data_session_open). The description reinforces that origin with 'after data_session_open' but adds no new constraint, so the baseline 3 applies.

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 action and object: purchase per-query access to live data listings, and names the concrete listing (statwatch, STAT News pharma/biotech, 0.01 USDC/query). The one ambiguity is that 'Buy' and 'Returns fund instructions' sit side by side without saying explicitly how this differs from the sibling data_session_fund, so the reader must infer that no payment executes here.

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?

Offers a clear alternative for the free path ('first taste free via data_preview') and a prerequisite ordering ('after data_session_open'), which is genuine routing guidance. However, it never disambiguates this tool from data_session_fund or data_session_attach_escrow, which an agent would have to choose between in the same workflow.

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