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

Annotations already declare readOnlyHint=true, destructiveHint=false, and closed-world scope, so safety is covered. The description adds useful non-annotation context: that it is free, that new prepaid-credit sales are disabled in v4, and that historical credits are redeemable via a separate compatibility path — real behavioral/product-state context beyond the schema.

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 tight sentences with the 'FREE read-only' descriptor front-loaded and the compatibility caveat second. No filler, though the second sentence leans toward product-state trivia rather than tool behavior.

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 and a declared output schema, the description need not explain return values, and it supplies enough framing (legacy/compatibility status, free read-only) for correct invocation. It stops short of saying what the status enumerates, but nothing critical is missing for a parameterless read.

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 there is nothing for the description to disambiguate; the baseline of 4 applies. No misleading parameter claims are made.

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 communicates that this is a read-only status resource about legacy credit compatibility, and 'FREE' plus 'read-only' frame it as a query. However, it never states the actual verb or what the tool returns (a list of credit options? a status report?), leaving the precise purpose vague even if the general domain is clear.

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?

There is no explicit guidance on when to call this tool versus siblings, nor any named alternative. The mention of 'legacy' and 'historical paid credits' implies the tool is only relevant in a compatibility scenario, but the agent must infer that condition rather than being told it.

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