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

With no annotations, the description carries the full burden and does well: it discloses data source, refresh cadence (every business day), cache TTL (one hour), and even the paid x402 cost ($0.02/call in USDC on eip155:8453). It stops short of error behavior or rate-limit details beyond the cache.

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?

Front-loads the purpose, then freshness/caching, then the usage trigger and price. No wasted words, though the trailing x402 pricing sentence is somewhat appended rather than smoothly integrated.

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 no-annotation tool with no output schema, it covers source, freshness, caching, and cost, and sketches the two return shapes (rate table vs. converted amount). It does not detail the exact response structure, which is the only meaningful 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% with four enum-constrained params, so the schema already documents base/from/to/amount/date/op. The description only echoes the concepts ('base currency', 'any amount') and the '30 currencies' count, adding little beyond the schema. Baseline 3 applies.

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 resource and the two operations offered: a full ECB rate table against any base currency, or cross-rate conversion of any amount. It names the data source (ECB via frankfurter.dev) and scope (30 currencies), which an agent can distinguish from the crypto_price and converter siblings.

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?

Explicitly says 'Use this when an agent needs to live ECB reference rates for 30 currencies,' giving a clear positive trigger. It names no alternatives or exclusions, but the sibling set contains no other fiat-FX tool, so the routing gap is minor.

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