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

Discloses that it sources real-time rates from CoinAPI, requires a CoinAPI key, and consumes CoinAPI quota—a non-obvious operational cost. Even with no annotations, this adds meaningful behavioral context. It does not mention response format or error handling, but the quota warning and key prerequisite strengthen transparency beyond baseline.

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 moderately lengthy but every sentence contributes: function, examples, usage guidance, alternatives, and prerequisite note. It is front-loaded with the core purpose and logically organized, though the multiple alternative references could be condensed without losing information.

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, the description covers purpose, use cases, alternatives, prerequisites, and quota implications. It lacks an explicit statement of return value (converted amount), but that is easily inferred. Overall it is complete enough for an agent to select and invoke correctly.

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 descriptions already fully document each parameter (amount, from, to) with valid formats and case-insensitivity. The description adds value by clarifying supported conversion pairs (crypto-to-fiat, fiat-to-crypto, cross-crypto) and that amount is denominated in the 'from' currency, but this does not significantly exceed the schema's 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 explicitly states the tool converts amounts between crypto and fiat or crypto-crypto pairs, with concrete examples (BTC/USD, BTC/ETH). It distinguishes itself from sibling tools by name (crypto_price, currency_convert), making its scope unmistakable.

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?

Provides explicit when-to-use guidance: 'Use crypto_fx_rates when the conversion involves at least one cryptocurrency and a specific amount must be converted.' It also names alternatives (crypto_price, crypto_price_lite, currency_convert, currency_fx_lite) with clear conditions, covering both crypto-only and fiat-only scenarios.

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