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 real behavioral value beyond that: the exact snapshot instant and timezone, that missing platforms are still marked rather than dropped, and that a spread is computed. It does not describe ordering or format of the comparison, but the added output-shape disclosure is genuine.

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 dense sentence that front-loads the comparison scope and then the output traits. No wasted wording, though the phrase 'on 1 January 00:00 Dutch time of the given year' is compressed to the point of requiring a second read.

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 only two fully documented parameters, no output schema, and annotations covering safety, the definition supplies enough: what the result set contains and how gaps and spread are reported. Minor remaining gap is the shape of the six-platform payload, which is not described.

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 the schema already documents both 'coin' (ticker/name/slug, case-insensitive) and 'year' (range 2014–2026, 1 January reference). The description adds only the Dutch-time timezone qualifier, which is a small but non-trivial clarification beyond the schema; 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 states a specific resource and scope: all six platforms for one coin at one timestamp (1 January 00:00 Dutch time of the given year), plus what the response contains (missing platforms marked, spread between low and high). It is clearly distinguishable from price_history (time series) and get_reference_price (single price), though it never names those siblings to route the agent explicitly.

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 guidance on when to pick this over get_reference_price or price_history, and no stated prerequisites. The only contextual hint comes indirectly from the schema ('for the tax return over that year'), which is not part of the description's guidance.

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