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

Annotations already establish read-only, idempotent, non-destructive, closed-world behavior. The description adds useful context beyond annotations: data provenance ('CryptoKeyhole's own hourly price indexes'), historical coverage ('daily closes since August 2015'), and the effect of supplying dates. It does not mention auth or rate limits, but for this public read-only metric that is a minor gap.

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?

The description is a single dense but front-loaded sentence that identifies the resource first and then lists the returned metrics and data source. It avoids filler, though the run-on structure makes it slightly harder to scan than a bulleted or multi-sentence presentation.

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?

For a simple two-parameter, read-only ratio tool with no output schema, the description is largely complete: it names the returned metrics, explains the date-range behavior, and gives data provenance and historical coverage. It lacks explicit output format details, but the annotations and schema cover the remaining operational context.

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 coverage is 100%, so both optional date parameters and their defaults are fully documented in the schema. The description adds only a light semantic hint that dates produce a change between two UTC days, without restating or extending the schema's default behavior (today / last 365 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?

The description clearly identifies the specific resource (ETH/BTC ratio) and the returned metrics (30-day change, 200-day average, all-time high close, and date-range change). It does not explicitly distinguish this from siblings such as get_price_history or fetch_metric, so it falls short of full sibling differentiation.

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?

There is no explicit when-to-use guidance or routing to alternatives among the many sibling tools. The phrase 'when dates are given' describes conditional behavior, not when an agent should choose this tool over get_price_history or fetch_metric.

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