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

Annotations already declare readOnlyHint=true and openWorldHint=false, so the safety profile is covered. The description adds genuinely useful behavioral context beyond that: the call is free and spends no credits, which matters in a toolset where most siblings presumably consume credits, and it discloses the shape of the returned breakdown. It does not cover auth/connection failure behavior, which keeps it from a 5.

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 with no waste: the action and resource come first, the return breakdown second, and the cost caveat last. Every clause earns its place.

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 no parameters and no output schema, the description carries the burden of explaining the return value, and it does so by naming the three credit buckets including expiry semantics. Missing only minor operational context, such as what happens if no account is connected.

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 schema has nothing to document and the baseline of 4 applies. The description correctly implies no inputs are needed to scope the balance lookup.

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 ('Show the credit balance on the connected AppmanAi account') and enumerates the breakdown it returns (bonus credits with expiry, monthly allowance, non-expiring credits). It does not explicitly differentiate itself from the sibling user_api_usage, which is the closest alternative for account-level usage information.

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?

Usage is implied — an agent should call this when it needs to know remaining credits — but there is no explicit when-to-use guidance, no mention of when to prefer user_api_usage, and no stated preconditions such as needing a connected account.

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