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

Annotations already declare readOnlyHint=true and destructiveHint=false, but the description adds substantial behavioral context beyond that: requires authentication, school-scoped data, live values reflecting orders/refunds, and the caution to recheck before assuming funds. It also emphasizes no side effects, which reinforces the read-only annotation without contradicting it.

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 description is front-loaded with the most important fact ('Read-only lookup - never moves funds or has side effects') and every subsequent sentence earns its place: auth, scope, units, freshness, and usage guidance. It is detailed but not bloated, each clause adds distinct value.

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 zero-parameter tool with an output schema, the description covers everything needed to call it correctly: authentication requirement, per-school scoping, return format (cents and formatted), live-value semantics, and when to invoke it. An agent has all necessary context.

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 input schema has zero parameters, so the baseline is 4. The description doesn't need to explain parameters because there are none; it instead explains what data the tool operates on (caller's balance, active school), which is the relevant semantic content.

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: it 'returns only the caller's spendable wallet balance.' It also scopes the operation precisely to the caller's active school, in cents and formatted, which separates it from any other balance-related query. This clearly distinguishes it from the mutation-heavy sibling list.

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 gives explicit when-to-use instructions: 'Call before pay_lunch_order_draft or register_for_event to confirm the user can cover the charge.' It also provides a when-not exclusion ('not needed for read-only lookups') and contextual scoping guidance about per-school balances.

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