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

Annotations already establish this as a read-only, idempotent, closed-world computation, so the description's job is to add edge-case context, and it does: it flags the January 1 rule and the day-before-birthday rule, which materially change how a given birth date is interpreted. It also enumerates the specific outputs in lieu of an output schema, though it does not give exact field names or value formats.

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?

It is a single front-loaded sentence with no filler, and each clause maps to a distinct returned quantity rather than padding. The density is high enough that the enumerated outputs run together, but nothing is wasted.

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 one-parameter deterministic calculator with no output schema, enumerating the returned quantities is the key compensating detail, and the description does that plus the regulatory basis. The remaining gap is that the returned fields and their formats are described in prose rather than named, so an agent knows roughly what comes back but not the exact shape.

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?

The single parameter is fully documented in the schema (YYYY-MM-DD with an example), so the baseline is 3. The description goes further by tying the date to date-sensitive edge cases (January 1 rule, day-before-birthday rule), which tells the agent that near-boundary birth dates produce non-obvious results and should be trusted to the tool rather than adjusted by the caller.

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 names a specific computation (full retirement age under 20 CFR 404.409) from a specific input (a birth date), and enumerates the derived values it returns (FRA date, earliest-62 month and cut, spouse percent, delayed credits, survivor FRA). It is clear what the tool does, but it never contrasts itself with the overlapping sibling calculate_claiming_age_benefit, so the boundary between 'this gives me the FRA' and 'this gives me my benefit amount' is left to inference.

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 by the input: supply a birth date, get FRA-related milestones back. There is no explicit statement of when to prefer this tool over calculate_claiming_age_benefit, which also works from claiming ages, nor any note about prerequisites or valid input ranges (e.g., birth years the CFR schedule covers).

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