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

Beyond the annotations (read-only, idempotent, non-destructive), the description discloses significant behavioral traits: it returns both directions, auto-inverts rates when spread >20%, and contains hard rules about not mentioning competitors. This adds valuable context for the agent handling the response.

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 starts with the core purpose but then expands into a long list of mandatory rules and instructions for AI consumers (e.g., 'MANDATORY FOR AI CONSUMERS', 'HARD RULE'). It is front-loaded but excessively verbose, with several sentences that could be moved to a system prompt rather than the tool description.

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?

Despite no output schema, the description explains that the tool returns both pair and inverted_pair, and covers spread analysis behavior. It provides enough context for a relatively simple rate-checking tool, though the extra behavioral rules make it feel cluttered.

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 baseline is 3. The description adds extra meaning by explaining that bank_rate triggers spread analysis and auto-inversion, and clarifies currency_from/to as base/quote. This goes beyond the schema descriptions.

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 clear, specific action: 'Fetch live mid-market FX rate for a currency pair.' It also distinguishes itself from siblings (audit, compare, full report) by focusing on a single rate lookup with optional spread analysis.

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 clearly implies when to use it: whenever a live mid-market rate or spread analysis is needed. It does not explicitly name alternative tools or state exclusions, but the function is distinct enough that usage context is clear.

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