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

The annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and closed-world scope, so the safety profile is fully covered elsewhere. Beyond that, the description adds almost nothing: it does not say what happens with an invalid or expired code, whether exhausted codes report zero, or whether the value is cached. 'On this site' is the only added scoping context.

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?

One short sentence with no filler, and the key object (credits remaining on a redeem code) is front-loaded. It is appropriately sized for a single-parameter read tool, though the phrasing 'How many credits a redeem code has left' is a question rather than a declarative statement of 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?

For a one-optional-parameter read tool with fully described schema and complete annotations, the definition is close to sufficient. However, with no output schema, the description should state the return shape or the zero/error case for an invalid code, and it does neither.

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 coverage is 100% and the single optional 'code' parameter is documented in the schema, including the Authorization: Bearer fallback. The description only echoes that a redeem code is involved, adding no format, case, or precedence details beyond the schema. Baseline 3 applies.

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 gives a specific resource and outcome: the number of credits a redeem code has remaining. It is clear enough that an agent can distinguish a balance check from generating or inspecting a code, though it never names the siblings to sharpen the boundary and leaves the verb implicit (the name alone, 'balance', is vague).

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 when-to-use guidance, no statement of preconditions (e.g. the code must exist or be unexpired), and no mention of how this differs from redeem_info, which an agent could plausibly confuse with it. Usage is only inferable from the sentence itself.

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