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

Annotations cover the safety profile (readOnlyHint=true, destructiveHint=false), so the bar is lower. The description adds information annotations do not carry: that access requires an x402 payment authorization, which is critical before an agent calls it. It stops short of explaining pagination, cost magnitude, or what the base universe actually contains.

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 sentences, zero filler, with the primary purpose front-loaded and the disambiguation second. The constraint about payment and the sibling exclusion each earn their place. Slightly dense jargon (ST-IM / STIM) keeps it from being maximally clear.

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 six-parameter tool with no output schema and no annotation-level parameter guidance, the description leaves too much undefined: no filter semantics, no notion of what the 'base universe' contains or how it differs structurally from the thresholded list, and no return-shape hints. The payment disclosure is helpful but does not cover the operational gap.

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?

All six parameters have 0% schema description coverage, and the description says nothing about any of them. Opaque names like cs_only, include_mast, and min_prob13wk are left entirely unexplained, so an agent cannot know what any filter does without guessing. The description fails to compensate for the coverage gap.

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 names a specific resource (the API-authored base ST-IM selection universe) and explicitly distinguishes it from the thresholded published STIM Select list, which is its nearest sibling (get_stim_latest / get_stim_history). The verb 'Purchase' is unusual and slightly obscures that this is fundamentally a retrieval endpoint, but the resource identity is unambiguous.

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?

'This is not the separately thresholded published STIM Select list' gives a clear exclusion that lets an agent route away from this tool when it wants the thresholded list. However, it never names the alternative tool or states the positive condition ('use this when you need the raw universe'), so the driver is left to inference.

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