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

Annotations already declare readOnlyHint, idempotentHint, etc. The description adds that the tool is 'keyless, offline' and provides an example output, which gives behavioral context beyond the annotations. It does not discuss error handling or edge cases, but given the simple nature and annotation coverage, this is sufficient.

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 two sentences plus an inline example. It front-loads the core purpose and provides a concrete illustration, with no extraneous words. Every sentence 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?

For a tool with three simple parameters and no output schema, the description is complete. It explains the transformation, input constraints (ISO currency, BCP-47 locale), and gives an example. Annotations cover safety and idempotency. No further context is needed.

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?

Input schema coverage is 100% with clear parameter descriptions. The description adds value by specifying that 'currency' must be an ISO 4217 code and that the default locale is 'en-US', along with an example that clarifies the expected format. This provides context not present in the schema alone.

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 states the tool formats a number as localized currency, with a concrete example showing input and output. It uses a specific verb ('Format') and resource ('number as localized currency'), and the sibling list includes 'format_number', indicating that this tool adds currency-specific logic. The purpose is unambiguous and well-differentiated.

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?

The description mentions 'keyless, offline' but does not explicitly state when to use this tool versus alternatives like 'format_number'. There is no guidance on when not to use it or what distinguishes it from similar tools. The usage context is implied rather than clearly articulated.

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