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

Annotations already declare read-only and idempotent, and the description adds valuable behavior context by outlining exactly what information is returned and explicitly stating 'Read-only — costs no credits.' This goes beyond the safety hints, though it does not describe edge cases or failure modes.

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?

The description is two sentences, front-loaded with the core purpose, and every clause adds meaningful detail (plan, credits, limit, reset, rate limit, upgrade link, usage cue, credit cost). No redundancy or filler.

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 zero parameters, strong annotations, and no output schema, the description covers all necessary context: what the tool checks, what specific data it returns, when to use it, and its safety profile. It fully compensates for the lack of an output schema.

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 has zero parameters, so the description carries no parameter burden. Per guidelines, 0 params earns a baseline of 4, and the description appropriately focuses on the tool's purpose and outputs rather than nonexistent inputs.

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 states a specific action ('Check the Rendex account') and enumerates distinct outputs: plan, credit usage vs monthly limit, reset time, per-minute rate limit, and upgrade link. This clearly distinguishes it from sibling tools like render_artifact or watch_list.

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?

Explicitly states when to use it: 'whenever the user asks about their usage, remaining quota, current plan, or how to get more renders / stop hitting limits.' This provides clear context for tool selection and even notes it costs no credits.

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