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

Annotations already declare readOnlyHint, openWorldHint and destructiveHint, so the safety profile is covered. The description adds real context beyond that: the data source is the Central Bank of Russia and the tool covers precious metals as well as currencies. It still omits things like date-boundary behaviour or weekends/holidays, so it stays adequate rather than rich.

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?

A single tight sentence that front-loads the resource and ends with the temporal scope. No filler, no repetition of the title.

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 two-parameter read tool with annotations and full schema coverage, the description is minimally sufficient. With no output schema, a brief note on the returned shape (rate value, nominal, date) would have helped, and the code vocabulary ('USD, EUR, XAU и т.п.') is only in the schema, not the description.

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% – both 'code' and 'date' are documented in the schema, including the yyyy-mm-dd format. The description adds nothing beyond the schema, 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?

States a specific verb (returns the rate) and resource (CBR currency/precious metal rate) scoped to a date. It is unambiguous which sibling it is versus the check_*/lookup_* family, though it never explicitly names an alternative. Clear purpose, but not differentiated as sharply as a top-tier 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 only implicit: the name and the 'на указанную дату' phrase signal 'call this to fetch an official rate for a date'. There is no explicit when-to-use, when-not-to-use, or alternative guidance (e.g. live rate vs. historical, or which codes are valid).

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