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

Annotations already cover read-only/open-world/non-idempotent, and the description adds real value: the ~5-minute recompute during market hours (which justifies idempotentHint=false), the subscription-plus-sign-in requirement, the x402 per-call payment path, and the failure mode (PaymentRequired object with no data). Returned field semantics are not described, holding it below 5.

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 its cadence, then handles the commercial/access model in tightly packed clauses. The final sentence about PaymentRequired is essential, but the 'Live intraday version.' fragment is slightly redundant with the opening sentence.

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 agent needs the access model and the failure behavior most, and both are supplied. The remaining gap is that the named payload elements (verdict, mode, permission ladder) are never explained, so an agent knows what it gets only by name.

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?

Zero parameters with 100% schema coverage, so the schema baseline of 4 applies; there is nothing for the description to clarify and it does not need to.

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 concrete resource (live intraday stock market regime, including the crypto book) and enumerates the payload conceptually (verdict, mode, permission ladder) with a refresh cadence. The 'Live intraday version' line plus the sibling get_market_regime makes the live-vs-historical split 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?

Explicitly states the access conditions: subscribe to Coil Live and sign in via the connector, or pay per call with an x402 wallet. It does not explicitly route agents to the non-live get_market_regime sibling for historical data, leaving that inference to the name, which keeps it short of a 5.

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