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

Annotations already declare readOnlyHint=true, idempotentHint=true, and openWorldHint=false, so the safety profile is covered. The description adds useful context about the shape of the output (nest egg projection plus withdrawal longevity) and supplies a sample result, but says nothing about the return format, currencies, or precision. With annotations carrying the behavioral burden, a 3 is appropriate.

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 plus a link; the concrete example is front-loaded and the purpose sentence follows immediately. It is compact, though the opening dollar figure is illustrative rather than instructional, and the bare URL contributes little.

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 9-parameter calculator with full schema coverage and read-only annotations, the description states enough to call it, and it partially describes the output. However, with no output schema, it never spells out what values are returned (nest egg, depletion age, currency handling), leaving a gap against the tool's complexity.

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 every parameter already has its own description, range, and default. The lead example (age 35, 7%, $800/month, $1.38M by 65) maps intuitively to the age, rate, monthly, and retireAge inputs but adds no semantics beyond the schema. Baseline 3 when the schema does the heavy lifting.

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 gives a specific verb and resource: it 'projects your nest egg and how long withdrawals will last', reinforced by a concrete worked example. It is clear what the tool computes, but it never distinguishes itself from close siblings like 401k_calculator, roth_ira_calculator, or savings_goal_calculator.

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 when-to-use or when-not-to-use guidance. An agent cannot tell from the description whether this or 401k_calculator / savings_goal_calculator is the right pick, and no prerequisites are stated.

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