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

Annotations only declare the mechanical safety profile (non-read-only, non-destructive, non-idempotent, closed-world). The description adds real context beyond them: the redemption grants time-based Premium that stacks after any current term, and an API key is required. It stops short of stating what happens to an invalid/expired/already-used code, which matters given idempotentHint=false.

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?

Three short sentences, front-loaded with the action and resource, then effect, then prerequisite. Every sentence carries distinct information with no padding.

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-parameter, no-output-schema tool this covers the essentials: what it does, what it yields, and the auth requirement. The main omission is failure behavior (expired/reused/invalid codes), which an agent would need in order to interpret errors correctly.

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?

With a single parameter at 100% schema coverage, the schema already documents the code format, case-insensitivity, and optional dashes. The description's parenthetical CR-XXXX-XXXX-XXXX-XXXX repeats that information rather than adding new meaning such as where the code comes from or whether whitespace is trimmed.

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 ("Redeem") and a specific resource (a credit code in CR-XXXX format) and immediately explains its effect: days of Premium added after any existing term. No sibling tool in the 40-item list touches code redemption, so the purpose is unmistakable without needing comparative language.

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?

"Needs a key" gives an explicit prerequisite, and "for the key owner" clarifies the account the redemption applies to. There are no alternatives or exclusions to name because this is a single-purpose one-shot action, but it doesn't say what to do if redemption fails or whether a key can be reused.

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