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

Annotations already declare readOnly, idempotent, non-destructive, closed-world behavior, so the safety profile is covered. The description adds real context beyond that: the response includes the qualification plus a reason, and is grounded in IRS Publication 970, telling the agent the output is an authoritative determination rather than a bare boolean.

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?

One sentence, front-loaded with the action ('Say whether a college expense is a qualified 529 expense'), with parenthetical examples and the citation trailing. No filler; every clause carries information.

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, read-only lookup with no output schema, the definition gives enough to invoke correctly: input semantics, the determination returned, and its source. It does not describe the exact shape of the result (boolean vs. text, edge cases like 'no' answers), a minor gap given the tool's simplicity.

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 has 100% schema coverage ('What the money was spent on'), which sets a baseline of 3. The description goes beyond it by listing representative values ('laptop', 'off-campus rent', 'gas', 'student health insurance'), showing the expected granularity and vocabulary of the input, which is genuinely useful for a free-text field.

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?

States a specific verb and resource: decides whether a college expense is a qualified 529 expense. Concrete input examples ('laptop', 'off-campus rent') and the authority (IRS Publication 970) make the scope unmistakable, and no sibling tool (compare_529_plans, get_529_plan, estimate_college_cost, school lookups) does anything similar, so it is trivially distinguishable.

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 implies the use case through examples but never states when to call this versus alternatives, nor any exclusions or prerequisites (e.g., jurisdiction, per-student limits). With no directly competing sibling, implied usage is tolerable but the routing guidance is thin.

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