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

Although annotations already declare readOnlyHint and openWorldHint, the description adds substantial operational context: Coinbase as the primary source with Kraken as fallback, pair paths direct or through USD, rate timestamp, and that failed calls are not charged. It also discloses the $0.002 USDC x402 payment model and states the tool is information only, not financial advice.

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 front-loaded with the core conversion purpose and is dense with useful operational detail. Some clauses are packed into long sentences, but nearly every clause contributes to correct invocation, pricing awareness, or scope boundaries.

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?

An output schema exists, so return-format explanation is not strictly required, yet the description still covers the key returned elements: rate, converted amount, pair path, and time. Combined with source fallback, payment, and exclusion details, it is complete enough for an agent to call the tool 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?

The input schema has 100% description coverage, documenting from, to, and amount including symbol examples and the amount default. The description does not add much parameter-level meaning beyond what the schema already provides, so the baseline score of 3 is appropriate.

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 states a specific verb and resource: convert an amount between a crypto and a fiat currency, or between two crypto assets, at the current spot price. It also names what it is not by refusing fiat-to-fiat conversion and directing that use case to the FX tool, so an agent can distinguish it from 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?

The description gives clear usage context, including that it returns a spot rate rather than an executable quote, with no fees or slippage. It explicitly excludes fiat-to-fiat conversion and names the alternative tool for that case, leaving little ambiguity about when to select this tool.

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