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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false, and openWorldHint=true. The description adds meaningful operational context beyond those annotations: a fixed 0.01 USDC cost on Base x402 and the X-Provider-Key header for customer-owned provider credentials.

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 two sentences with the calculation purpose front-loaded, followed by critical cost and credential information. There is no wasted 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?

For a simple read-only calculation with rich annotations and no output schema, the description covers purpose, cost, and auth. However, it omits numeric units/format and output conventions such as whether CAGR is returned as a decimal or percentage, leaving some ambiguity for correct invocation.

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 nominally 100%, so the baseline is 3. The description maps the inputs to initial/final values and elapsed years, but it does not provide units or format details even though the schema descriptions point to the operation description for those details.

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 uses a specific verb, calculate, and names the exact resource: compound annual growth rate and annualized gain from initial/final values and elapsed years. It is clearly distinguishable by function, though it does not explicitly contrast with sibling finance tools such as api_investment_return.

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?

There is no explicit when-to-use or when-not-to-use guidance, and no alternative tool is named among the many finance siblings. The only usage signal is implied by the required inputs.

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