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

Goes well beyond annotations: it discloses the auth model (subscription + sign-in), a pay-per-call fallback via x402, and the exact failure behavior (a PaymentRequired object and no data). These are behavioral traits the readOnly/openWorld/idempotent hints cannot convey.

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?

Front-loads what the tool returns and then covers access mechanics in three tight sentences. Slight redundancy between "Live intraday" in the first sentence and the standalone "Live intraday version" sentence, but nothing meaningfully wasteful.

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 no parameters and no output schema, the description carries the load and does so adequately: it names the candidate scope, the entry states, and the failure object. It stops short of describing the shape of a successful payload, which is the only remaining 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?

There are zero parameters and 100% schema coverage, so the baseline is 4. The description correctly adds behavior-like qualifiers (READY/SETTING UP entry windows, asset-class scope) rather than re-documenting nonexistent parameters.

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 verb+resource: live intraday ranked buy-list candidates across US stocks and ETFs (with the crypto book noted). The phrase "Live intraday version" cleanly separates it from the non-live sibling get_buy_list without needing the schema.

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?

Clearly states the conditions under which it returns data (Coil Live subscription + connector sign-in, or an x402 wallet) and the condition under which it yields nothing. It does not explicitly route to the non-live get_buy_list for as-of/historical reads, so alternative guidance is implied rather than stated.

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