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

Annotations already declare this is a read-only, non-destructive, closed-world operation, so the description earns credit for the extras it adds: the required OAuth scope (balance:read), the account-linking precondition, and the EUR denomination. It stops short of saying what happens when preconditions fail (error shape or empty result), which would round out the behavioral picture.

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?

Three short sentences with no filler. The eligibility constraint and the negative guardrail are front-loaded before the softer prerequisite detail.

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?

With an output schema present, the description needn't explain return values, and it covers auth scope plus the account-linking requirement. The only meaningful gap is failure behavior when the caller is not PRO or has no linked account, which matters given the explicit guest-flow warning.

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 tool takes zero parameters, so the baseline is 4 and there is nothing for the description to clarify. The description correctly spends no words on argument semantics and instead invests in preconditions.

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 ('Returns the authenticated PRO user prepaid credit balance in EUR') and scopes it to a named audience. This is clearly distinguishable from siblings like guest_order_lookup or list_orders, which deal with orders rather than account balance.

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?

Gives explicit eligibility ('PRO accounts only'), an explicit exclusion ('do NOT call for guest checkout flows'), and the prerequisite (linking a doctorSIM account). An agent has everything needed to decide whether to call this or fall back to another path.

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