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

Annotations already cover readOnly/idempotent/non-destructive, yet the description still adds real value: it discloses the required billing:read scope, which is the most common failure mode when calling, and explains the workspace-shared wallet semantics so the agent knows the balance is not per-user. It omits any note on staleness or caching of the balance.

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 dense sentence that front-loads the verb and resource, then the returned fields, then the workspace-wallet caveat, then the scope requirement. Every clause carries distinct information with no restatement of the name.

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 output schema, the description correctly compensates by listing the five values returned. For a zero-parameter read tool this is close to complete; only the unit/expiry semantics of the different balances and any staleness behavior are left implicit.

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 there is nothing the description needs to disambiguate; a baseline of 4 applies. The schema is empty with additionalProperties false, matching the parameterless description.

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 ('Get the posterly AI credit balance') and enumerates exactly what the payload contains: available balance, monthly allowance left, purchased packs, plan tier, next reset. It does not explicitly distinguish itself from near siblings like get_subscription or manage_plan, so an agent must infer the boundary.

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?

No when-to-use guidance is given, no prerequisites for calling, and no naming of alternatives such as get_subscription for billing details or manage_plan for changing tiers. The clause 'this is the balance the caller can actually spend' clarifies interpretation, not invocation timing.

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