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 real domain context beyond that: the hard-coded 2026 limits, that MAGI drives an income phase-out, and that the tool performs an annual-tax-drag comparison against a taxable account.

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?

A single front-loaded sentence covers what is checked and what is projected, followed only by a reference URL. Nothing is padded, though the URL is dead weight for an agent deciding whether to invoke the tool.

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 an 8-parameter, all-optional calculator with no output schema, the description adequately signals the two outputs (limit/phase-out eligibility and a projected balance comparison). It does not mention that all 8 inputs carry defaults or what the tool reports when MAGI exceeds the phase-out range, leaving a small gap.

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 age, MAGI, rate, filing, balance, taxRate, retireAge and contribution are already documented in the schema. The description reinforces the 2026 contribution limit context ($7,500 / $8,600 at 50+), which matches the schema's own contribution note but adds no new syntax or format detail.

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 verb-and-resource pair: check the 2026 Roth IRA limit and MAGI phase-out, then project the tax-free balance against a taxable account. That is concrete and unique among the many retirement siblings (401k_calculator, retirement_calculator, rrsp_calculator), though it never explicitly differentiates itself from them.

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 use case is implied by the two-part framing ('check the limit... then project...'), which tells the agent this is for contribution-limit/eligibility questions plus a Roth-vs-taxable comparison. However there is no explicit when-to-use, no when-not-to-use, and no sibling alternative named.

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