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

Annotations already cover the safety profile (readOnlyHint=true, destructiveHint=false), so the description earns credit for adding behavioral context beyond them. It discloses that the rate is indicative and rounded and that the tool returns bid, ask, and mid rates, which matters for interpreting output. It does not mention authentication or rate limits, but those are secondary here.

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?

Three tight sentences: purpose first, then output and limitation, then a concrete example. Every sentence earns its place with no filler or redundancy.

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 simple read operation with a fully described schema and annotations covering safety, the description adequately covers output semantics (bid/ask/mid, rounded, indicative). It omits whether unsupported currencies produce an error or should be checked via list_supported_currencies, which is a minor gap.

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%, establishing a baseline of 3. The description's example ('base=GBP, quote=USD returns the GBPUSD rate') adds meaning by clarifying that the base/quote ordering defines the pair, which the schema descriptions alone do not spell out.

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 gives a specific verb and resource: 'Get an indicative spot FX rate for a currency pair.' It implicitly distinguishes itself from the forward-rate sibling by saying 'spot,' but never explicitly names an alternative tool such as get_forward_rate, so it falls short of a 5.

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 phrase 'for illustration purposes only — not for execution' signals a usage context and a clear limitation. However, it offers no explicit when-to-use guidance versus alternatives like get_forward_rate, so the guidance remains implied rather than actionable.

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