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

With no annotations provided, the description carries the full burden. It discloses that the source is an 'open public exchange rate feed suitable for informational use', indicating reliability limitations. It explicitly states the output (converted amount and rate applied) and excludes cryptocurrency pairs. While it doesn't discuss rate limits or error handling, it offers meaningful behavioral context beyond a mere conversion claim.

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 dense but every sentence earns its place: purpose, output, fallback context, preference alternatives, and exclusions. It front-loads the main action and then systematically addresses sibling tools, making it well-structured for an agent navigating many related tools.

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 3-parameter tool with no output schema and no annotations, this description is highly complete. It covers what the tool does, what it returns, when to use it versus alternatives, its suitability for informational use, and a clear exclusion for crypto pairs. Given the sibling complexity, no critical context is missing.

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%, with each parameter (to, from, amount) already described with ISO 4217 and positivity constraints. The description adds that only fiat currencies are supported, which is a useful semantic clarification, but doesn't go beyond the schema's parameter-level documentation. Thus baseline 3 is appropriate.

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: 'Converts a monetary amount between two fiat currencies using live exchange rates'. It clearly distinguishes itself from siblings by naming alternative sources and specifying it does not support crypto pairs, directing users to crypto_fx_rates instead.

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?

Explicit guidance is given: use this tool when currency_convert or currency_fx_lite are unavailable or rate-limited. It also states when to prefer alternatives: prefer currency_convert/currency_rates for ECB-auditable rates for accounting, currency_convert_lite for minimal output with ECB backing, and currency_fx_lite for lightweight mid-market conversions. It even excludes crypto conversions.

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