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

Annotations already declare readOnlyHint, idempotentHint and openWorldHint=false, so safety behavior is covered. The description adds real context by stating the calculation flow (subtract contributions, add back past withdrawals) and the 2026 limit figure, but it says nothing about the shape of the result or edge cases such as ineligible years.

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?

The core calculation sentence earns its place, but the leading rhetorical question and the bare marketing URL (https://calcbright.com/tfsa-calculator) are filler an agent gains nothing from. It is not bloated, but it is not tightly front-loaded either.

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 seven-parameter, default-heavy calculator with no output schema, the description conveys what goes in conceptually and what comes out ('your room and how the account could grow'), which is enough to call it correctly. It stops short of describing the return structure, which is the only notable 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 every one of the seven parameters is already documented in the schema with defaults and ranges. The description paraphrases some of those concepts (contributions, withdrawals, growth) without adding format, unit, or interaction detail beyond what the schema provides. Baseline 3 is appropriate.

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 the resource (TFSA) and states what is computed: contribution room and potential account growth, including the $109,000 2026 limit. That is a specific purpose an agent can act on, though it never explicitly contrasts itself with TFSA-adjacent siblings like rrsp_calculator or 401k_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?

The framing question 'Eligible since 2009?' hints at the relevant scenario, but there is no explicit when-to-use statement, no prerequisites, and no named alternatives among the many sibling calculators. Guidance is left entirely to inference from the tool name.

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