get_credit_balance

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

Annotations already cover readOnly, non-destructive and closed-world, but the description adds context they cannot: the cost model (real API cost, capped at the tool maximum, must be available at call start) and the failure contract (out_of_credits plus a credits_needed field). The only gap is that it does not describe the shape of the returned balance/usage data.

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?

Purpose and trigger lead the text, followed by cost behavior, which is the right order. The cost-capping clause ('never more than the tool's maximum, which must be available when the call starts') is dense and takes a second pass to parse, but no sentence is wasteful.

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, read-only tool with no output schema, the description covers purpose, timing, cost semantics and the error case. What is under-specified is the return payload: 'credit balance and recent usage' leaves the fields and granularity of the usage data undefined.

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 for the description to disambiguate. Baseline 4 applies; no parameter discussion is needed or expected.

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 opens with a specific verb and resource: 'Return the user's Unilytics credit balance and recent usage.' That is unambiguous and tells an agent exactly which resource is produced, separate from the many get_* siblings that fetch project, skill, or citation data.

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?

It gives explicit triggers ('when the user asks about credits or before a run they want costed') and names free operations that do not need this check, which is real routing guidance. It stops short of naming alternative tools or stating when-not to call it, so it is short of a 5.

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