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

Annotations already cover read-only/idempotent/non-destructive and open-world scope, but the description adds materially more: per-call pricing ($0.002, 10 free/day), the x402 payment-required fallback, and error semantics (isError result, not charged on failure). It doesn't detail pagination or series size limits, which keeps it short of a 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-loaded with purpose and output, then usage, then pricing/errors in a predictable order. Slightly dense with parenthetical asides and one redundant restatement of return contents, but nearly every sentence carries information.

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, listing return stats is optional; the description covers cost, failure modes and the sibling boundary, which is what an agent needs. The unresolved hourly-window inconsistency is the remaining ambiguity an agent would hit.

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?

Schema description coverage is 100%, so the schema already explains asset formats, chain enum, days range and interval. The description adds only the 'same asset resolution as crypto_price' hint; notably it does not resolve the conflicting hourly limits (description/schema days field say 90 days, interval field says 30 days).

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 precise verb+resource (historical USD prices for crypto assets) with granularity and horizon, and enumerates the derived stats returned. It also explicitly contrasts itself with the sibling crypto_price, so an agent can route between them without opening either 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?

Contains an explicit 'When to use' clause: past prices and drawdowns here, current price via crypto_price on the specified server. The negative case and the alternative are both named outright.

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