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

Annotations already mark it read-only/non-destructive, and the description adds significant context beyond them: cache refreshed once daily so prices can be up to ~24h stale, a notice field embedded in the response, and paid access in USDC on Base. Freshness, cost, and payment mechanism are exactly the behavioral traits an agent needs.

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?

Four short sentences, front-loaded with what the tool returns, then the disambiguation, staleness caveat, and payment note. The parenthetical about the missing data source is slightly defensive but still earns its place as disambiguation.

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 an output schema present, return-value detail is unnecessary, and the description covers the remaining gaps: no params, read-only nature, data staleness, cost/payment, and scope boundaries. Nothing needed to call it 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?

Zero parameters, and the description confirms 'No input params', matching the empty schema. Baseline 4 for a param-less tool; nothing further to clarify.

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 ('see') and a precisely scoped resource: BTC/ETH price position vs the same day-offset in the 2016 and 2020 halving cycles, plus today's BTC dominance. This is a unique comparison that no sibling tool (funding rates, token risk, unlocks) covers, so an agent can distinguish it immediately.

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?

Provides clear context plus an explicit exclusion ('This is NOT a historical dominance comparison'), which steers the agent away from a common mistaken expectation. It does not name a specific alternative sibling tool, so it stops short of the full 5.

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