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

Annotations already cover read-only, idempotent, non-destructive and closed-world behavior, so the description's real contribution is the data-boundary disclosure: it returns only balance and pricing revision and 'does not reveal internal numeric account or user IDs'. That is genuinely useful context an agent cannot get from the schema. It stops short of stating auth requirements or error/empty-account behavior.

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?

Compact and front-loaded: trigger first, then return scope, then exclusions. The trailing 'Do not call for unrelated creative prompts' is slightly vague about where the boundary actually lies, but no sentence is wasted.

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?

An output schema exists so return values need no explanation, and the description correctly focuses on scope boundaries. The one real gap is the undocumented 2-parameter surface, which leaves the agent guessing at what include_guidance does.

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?

Schema description coverage is 0% and neither parameter is mentioned. The meaning of 'include_guidance' is entirely opaque, and 'lang' appears only as a 2-16 char string with a default. With low coverage the description needed to compensate and does not.

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 ('Check MixerAI coin balance' / 'Returns the current balance and active pricing revision') and immediately distinguishes itself from pricing tools by saying it 'does not price a generation', separating it from siblings like aimixer_quote and aimixer_estimate.

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 an explicit trigger ('when the user asks about their MixerAI coin balance or whether the connected account has funds') plus an explicit exclusion ('Do not call for unrelated creative prompts'). The agent knows both when to select it and when to route elsewhere.

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