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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is covered. The description adds genuinely non-obvious behavior: entries below min_sample are suppressed and returned as published:false with sample_size only, each entry carries an Ed25519 signature verifiable against a separate key endpoint, and no credentials are needed. Missing only operational edge cases such as future dates or unavailability errors.

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 text is front-loaded with purpose, then moves through response shape, suppression rule and signature protocol without filler. The dense field enumeration is justified because no output schema exists, though the clause count makes it heavier than strictly necessary.

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 provided, the description carries the full burden of describing return values and does so in detail (service vs token entry fields, signature envelope, suppression behavior). Only error and unavailability semantics are left unstated, a minor gap for a zero-required-parameter read.

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?

There is a single optional parameter with 100% schema description coverage; the schema already documents the YYYY-MM-DD format and the omit-for-latest behavior. The description restates the same defaulting rule without adding format or validation meaning, so the baseline 3 applies.

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 opens with a specific verb and resource ('Read Bitroad's daily price index') and scopes it to per-grade, per-currency values for the latest published UTC day or a given date. An agent immediately knows what it returns. It does not, however, contrast itself with the sibling pricing_oracle, 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?

It supplies the useful context that the tool works without credentials and is 'information only, not a benchmark', which implicitly marks it as a read-only lookup. It never states when to choose this over pricing_oracle or what to do about unpublished/absent days, so the when-to-use guidance remains implied rather than explicit.

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