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

Annotations already declare readOnly, idempotent, non-destructive behavior, so the bar is lower; the description still adds real behavioral detail by specifying the end-of-year contribution convention (which materially changes results) and the cost of 1 credit. It does not explain what output shape comes back (final value vs. a year-by-year schedule), which is the main remaining behavioral unknown.

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 tight sentences with the purpose and formula front-loaded, the timing convention immediately after, and the credit cost in a trailing parenthetical. Nothing is redundant and every clause adds usable 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?

With no output schema, the description should say whether the result is a single future value, a growth series, or both, and it does not. It also leaves the inflation-adjustment mechanism unspecified even though there is no inflation-rate parameter to drive it, which is a meaningful gap for a projection tool.

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; the description earns above that by mapping the formula terms onto the parameters — PMT as the annual addition arriving at year-end, n as years, r as the periodic rate — which the schema alone does not state. It still leaves "inflation_adjusted" ambiguous, since no inflation rate parameter exists and the description does not say what rate is assumed.

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 resource ("Projects investment growth") and pins down the method with an explicit compound-interest formula, so an agent knows exactly what computation happens. It never names or distinguishes the obvious siblings compound_interest, future_investment_value, or calculate_investment_return, so an agent cannot tell from the description alone why it should pick this one.

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 only implied: the mention of "optional annual additions and inflation adjustment" hints at when this fits better than a plain compound-interest call, but there is no explicit when-to-use statement, no exclusions, and no reference to the near-duplicate sibling tools in the catalog.

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