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

With no annotations provided, the description carries full burden. It discloses the one-time nature, the in-place upgrade, that it is free and unmetered, and the critical constraint that email must be explicitly provided by the user. Although it doesn't describe return values, the tool's side effects and safety boundaries are clearly stated.

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?

Four succinct sentences, each serving a distinct purpose: what it does, when to call, a critical safety rule, and a reassurance about the in-place upgrade. No fluff, no repetition, and the key information is front-loaded.

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?

The tool is simple—one required parameter, no output schema, no annotations. The description covers the action, trigger condition, constraints, and post-condition, making it self-sufficient for an agent to invoke correctly. Given the low complexity, this is complete.

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 input schema already has a clear description for the email parameter (100% coverage). The tool description adds extra meaning by emphasizing the prohibition against guessing or reusing emails and tying the email to the 'exactly as given' requirement. This goes beyond the schema's own wording, though only modestly.

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 opens with a specific action: 'Unlock 10 bonus calls on this trial key, one time only, in exchange for the user's email address.' It clearly identifies the resource (trial key), the condition (one time), and the exchange (email address). This distinguishes it from sibling tools like get_free_trial_key, which issue a trial key rather than adding bonus calls to an existing one.

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?

Explicit usage trigger provided: 'Call this when the trial limit is reached and the USER has chosen the free-bonus option and given you their email in this conversation.' It also gives a strong exclusion ('NEVER guess, invent, or reuse an email...') and clarifies that the key is upgraded in place with nothing to reconfigure. This leaves no ambiguity about when to invoke it.

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