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

Annotations already declare readOnlyHint, idempotentHint, non-destructive and openWorld, so safety is covered. The description adds genuinely useful context beyond that: the return is a percentage, the exact computation is disclosed, and a credit cost is stated — unusual and helpful operational information.

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 compact sentences: purpose plus formula first, output form second, cost last. Nothing is redundant and the most decision-relevant information is front-loaded.

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 three-parameter pure calculation with no output schema, the description covers purpose, computation, output unit, and cost — everything needed to call it correctly. Edge cases like zero start_value are minor and arguably belong in the schema.

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 coverage is 100%, so baseline is 3, but the description goes further by embedding each parameter in the formula, making clear that start_value is the denominator and years is an exponent denominator. That clarifies role and ordering in a way the one-line schema descriptions do not.

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 verb and named metric ('Calculates the Compound Annual Growth Rate (CAGR)') and even supplies the formula, so the operation is unmistakable. It does not, however, differentiate itself from finance siblings like calculate_investment_return, project_investment_growth, or compound_interest, which an agent may confuse it with.

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?

Usage is implied by the formula and the metric name — an agent knows this is for annualized growth between two values over N years. There is no explicit when-to-use/when-not guidance and no mention of the sibling tools that compute related return figures.

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