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

Annotations already declare readOnlyHint, idempotentHint and openWorldHint=false, so the safety profile is covered; the description adds the important trait that the simulation is deterministic rather than stochastic. It also previews the shape of the output (contributions, gains, total by year, plus a compoundsim.app URL), which the absence of an output schema makes valuable.

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?

Two sentences, with zero waste; the core operation is front-loaded and the disambiguation follows immediately. Nothing in it is filler.

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 7-parameter read-only calculator with full schema coverage and no output schema, the description supplies both the output shape and the deterministic-versus-stochastic distinction an agent needs. Only minor gaps remain, such as how inflation-adjusted outputs are presented while the schema already covers it.

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 100%, so every parameter, including the currency and language enums and the inflation semantics, is already documented in the schema. The description only echoes 'monthly contributions (plus an optional starting sum)' and does not add syntax or interaction details beyond the schema baseline.

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 ('deteministic compound growth of monthly contributions... at a fixed annual return') and names the sibling it is not. The contrast with simulate_portfolio is stated in the description itself, so the agent can separate the two without opening schemas.

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?

Explicitly routes the agent to simulate_portfolio 'for the range of outcomes of real assets,' which is the key alternative behaviour an agent would confuse this with. It gives a clear positive use context (fixed-rate, deterministic projections) but no explicit when-not or prerequisite notes.

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