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

Annotations already declare readOnlyHint, idempotentHint, and openWorldHint, so the safety profile is covered. The description adds genuine context beyond that: rates come live from the Frankfurter API and pass through an SSRF-safe outbound guard, which is useful for understanding latency and external dependency. It omits failure modes for invalid currency codes, which keeps it short of a 5.

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?

Two front-loaded sentences with no filler; the core operation leads and supporting detail follows. The mention of the SSRF-safe outbound guard is slightly implementation-flavored but still informative and brief.

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?

An output schema exists, so return values need no explanation, and annotations cover the safety profile. The description covers the source of rates and the historical-date capability, which is nearly everything an agent needs; only error behavior for unknown currency codes is unaddressed.

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 75% and all four parameters are constrained (ISO codes with min/max length, date regex, amount bounds). The description's 'ISO 4217 currencies' and 'historical dates' restate what the schema already says, adding no format or interpretation detail. Baseline 3 is correct.

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 (Convert) and resource (money between ISO 4217 currencies), which cleanly separates it from convert_units, convert_color, and convert_data_format. The rate source is named, so an agent knows exactly what operation it is getting.

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?

No statement of when to prefer this tool over neighbors such as convert_units, and no exclusions or prerequisites. 'Supports historical dates' hints at a use case but does not frame selection between alternatives.

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