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

Annotations already declare readOnlyHint, idempotentHint and destructiveHint=false, so safety is covered structurally. The description adds two non-obvious behavioral facts: the balance is per-connection bearer token, and the call itself has zero credit cost — real value beyond the annotations.

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?

Two short sentences, front-loaded with the resource and followed immediately by the cost caveat. No filler, no restatement of the title.

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 not be described. What remains absent is any note on failure modes (e.g., expired or missing token), which for a zero-parameter auth-scoped tool would be the only missing piece.

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?

Zero parameters, which sets the baseline at 4; the description correctly implies no inputs are needed because scope is derived from the connection's token rather than from arguments.

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) plus the exact resource (remaining prepaid credits) and scopes it to the credential in use ('the bearer token configured on this MCP connection'). No sibling tool touches credits, so there is no ambiguity to resolve; an agent knows exactly what this returns.

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 tells the agent this call is free and does not consume credits, which is the key decision input for calling it (e.g., safe to probe before a paid operation). It does not name alternatives or state when-not-to-call, but the sibling set is unrelated, so no routing guidance is required.

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