check_balance

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

With no annotations, the description carries the full behavioral burden. It discloses the return contents (total credits, usage, remaining balance), which is useful, and implies a safe read. However it says nothing about authentication requirements, rate limits, or whether the data is live/cached.

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?

One front-loaded sentence with an em-dash elaboration; no filler, no redundancy. Appropriate for the tool's simplicity.

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?

There is no output schema, but the description substitutes by naming the three values returned, and the zero-parameter schema needs no explanation. Auth/mutability details are the only real gaps, and those are minor for a read-only balance check.

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. There is no parameter syntax that requires explanation in the 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 (check) and resource (OpenRouter account balance), then enumerates the returned figures. An agent immediately knows what the tool does. It does not need sibling differentiation since the siblings (image generation tools) are unrelated, so a 4 rather than 5.

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 by the name and description — you call it to inspect account credit status. There is no explicit statement of when to use it, no prerequisites, and no alternatives named, but for a zero-argument read tool the intent is self-evident.

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