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

Annotations already declare readOnly/idempotent/non-destructive, and the description adds substantial context beyond them: ~1800s caching, X-Api-Key or x402 payment auth, HTTP 402 behavior for anonymous calls, $0.002 USDC cost, 30/min rate limit, and premium tier. This is exactly the behavioral detail annotations 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?

Well-labeled sections (Behavior, Auth, Cost, Rate limit, Returns, Guidelines) aid scanning, but the opening sentence and the 'Purpose:' line are a wasteful verbatim duplication, and the Tags/tier metadata is filler. Front-loaded but not tight.

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?

An output schema exists, so return values need no prose, and the description covers auth, cost, rate limits, caching, and usage cautions. Nothing an agent needs to invoke this correctly is missing.

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?

One parameter with 100% schema description coverage, so the schema already documents __x_payment fully. The description reinforces the auth header mechanism (X-PAYMENT / __x_payment) but adds no format or syntax beyond the schema. Baseline 3 is appropriate.

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 resource and computation: CME Bitcoin futures weekend gaps (Friday close vs Monday open) with fill status from BloFin candles. An agent can distinguish it from generic market-data siblings. However, the opening sentence and the 'Purpose:' line are verbatim duplicates, and sibling differentiation is limited to a pairing mention.

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?

Explicit guidance: 'Use for research / signal context,' 'Pair with cc.agent_strategy (paper) before any live order,' and 'Do not invent fills from this data alone.' It names a sibling and a caution, though it does not spell out when NOT to use it versus other signal tools.

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