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

Annotations already declare readOnlyHint, idempotentHint, and non-destructive behavior, and the description adds useful context beyond that: it will not change page or account state, will not access BetterOff customer data, and will not provide personalized financial advice. It also discloses the projection outputs, which strengthens transparency.

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 carry all essential information with no wasted words. The core purpose and output are front-loaded, and the safety/educational caveat is appended cleanly.

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 an output schema present and full parameter descriptions in the schema, the description adequately covers purpose, output behavior, and boundary conditions. It could go slightly further in explaining how the gap is derived or how displayMode affects results, but the available structured data fills those gaps.

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 the baseline is 3. The description mentions age, contributions, return assumptions, and income target, but it does not add parameter-level detail; the schema already documents every parameter, so the description is not required to compensate.

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 clearly identifies a specific verb and resource: it projects retirement savings, returns year-by-year balances, and estimates a gap with a 4% withdrawal assumption. It does not explicitly contrast itself with sibling tools like calc_fire or calc_savings_goal, so it is clear but not fully differentiated from alternatives.

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 context by framing the calculator as 'read-only educational' and based on 'caller-supplied public inputs,' implying it is for illustrative projections rather than personalized advice. It does not explicitly name when not to use it or point to sibling alternatives, but the context is strong enough for an agent to infer appropriate use.

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