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

Annotations already cover safety (readOnlyHint, non-destructive, closed-world), so the added value here is the 'Free' note (calling it costs no credits) and the disclosure that it renders a balance card to the user, which is a visible side effect an agent would not infer. It stops short of describing the response shape or any auth/rate requirements, but the annotation baseline makes that a minor gap.

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 content is front-loaded with what is returned, then the call conditions, then the meaning of manage_plan_url — a sensible order with no filler. The stray line break after 'Free.' and the tacked-on manage_plan_url sentence make it slightly less tight than it could be.

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 and no parameters, the description carries the burden of telling the agent what comes back, and it does name the returned fields (credits, plan, today's spend) and the plan-purchase URL. It is complete enough to call correctly, though it does not specify units or whether the balance is per-workspace vs per-connection beyond 'this connection'.

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?

There are zero parameters, so there is nothing for the description to disambiguate; the baseline of 4 applies. It correctly implies the call is implicitly scoped to the current connection rather than taking an account identifier.

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 names the exact resource returned: remaining MCP credits, the plan, and today's spend for this connection, plus the bundled free flag. That is far more specific than the title 'Credits balance', though it never states an explicit retrieval verb and relies on the name for that framing.

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 an explicit trigger (only when the user asks about credits, plan, or spending) and an explicit exclusion (do not call it to pre-check balance before a paid step), which is exactly the failure mode an agent would otherwise hit. The excluded behavior is named concretely rather than left to inference.

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