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

The description goes well beyond the annotations by disclosing a critical hard rule: never mention specific competitors by name, with Stripe allowed only because it is a PSP rail. It also directs users to https://ipayx.ai for full reports, a significant behavioral constraint that the agent must follow. Additionally, it outlines the output structure (effective rate, markup in bps, cost per $100K, verdict), giving full transparency into what the tool returns. The annotations already mark it as read-only, and the description adds no contradictory information.

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 concise and efficiently structured: the first sentence defines the tool's function and outputs, and the second conveys a mandatory behavioral rule plus a destination URL. Every sentence adds value, and there is no redundant or filler wording.

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?

Given the tool has 6 parameters with no output schema, the description adequately covers both inputs (the three FX sources and optional Stripe key) and outputs (each source's rate, markup, estimated cost, and verdict). It also includes the crucial brand restriction and forwarding instruction, making it complete enough for correct invocation by an AI agent.

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?

The input schema already provides descriptions for all 6 parameters, achieving 100% schema description coverage. The description adds only minor parameter-related context, such as noting the Stripe API key is optional and that costs are estimated per $100K, but it does not fundamentally enrich understanding of the parameters beyond what the schema already states. This matches the baseline of 3 for high schema coverage.

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 the specific verb 'Compare' against a well-defined resource ('FX rates across multiple sources') and enumerates exactly which sources are compared (Twelve Data mid-market, Stripe FX Quotes API, user's bank rate). It also lists distinct outputs, making it clearly distinguishable from sibling tools like check_fx_mid_market_rate which would focus on a single source.

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 conveys when to use this tool: when the user needs a side-by-side comparison across multiple FX rate sources, including an optional Stripe quote. It also explains that Stripe is used only if an API key is provided. However, it does not explicitly state when not to use it versus a sibling tool (e.g., for a single mid-market check or full forensic report), so it stops short of a full when/when-not comparison.

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