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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint, so the safety profile is covered. The description adds two real behavioral facts beyond that: the result is thinned to at most 60 points (a resolution ceiling) and price is only present where the source has it (possible nulls). Those are useful, but the description says nothing about ordering, timestamp granularity, or how the 60-point cap scales with the days value.

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?

One sentence, front-loaded with the resource and scope, with no filler. The parenthetical about price availability is slightly awkward but carries genuine information, so it earns its place.

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 output schema, the description must carry return-value burden, and it does so only partially: it conveys that points are sampled and that price may be absent, but not the point shape, time ordering, or sampling interval. Adequate for a simple read tool, but an agent still has to guess what each element looks like.

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% and every parameter carries its own explanation, including the metric enum meanings, so the baseline of 3 applies. The description's only marginal addition is that the '60 points' ceiling relates to the requested window, which is not spelled out explicitly enough to raise the score.

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: returns a metric's history for one market, with price where available, downsampled to at most 60 points. An agent immediately knows this is a time-series read, not a point-in-time lookup. It does not name the natural alternative (coin_snapshot) to sharpen the boundary, so it stops short of a 5.

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?

Usage is implied by the word 'history' and by the days parameter, but the description never states when to prefer this over coin_snapshot or other siblings, nor any exclusions. The 90-day cap lives only in the schema, not in the prose.

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