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

Annotations already declare readOnlyHint=true and destructiveHint=false, covering safety. The description adds valuable behavioral context: authentication is required on first use, and it enumerates the returned data (code, link, filleuls count, active count, tier, earnings). It does not discuss error cases or rate limits, but for a simple read tool this is sufficient.

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 sentences with zero waste. The user context is front-loaded, followed by the exact data returned. Every part of the description serves a clear purpose.

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?

Given the simplicity (no params, no output schema), the description is complete: it explains authentication needs and lists the return fields in detail. An agent has enough information to decide to call the tool and interpret its output.

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 has zero parameters, which is the baseline for a 4. The description does not need to explain parameters, and it instead usefully describes the return values, compensating for the lack of an output schema.

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 clearly indicates that the tool returns referral details for the logged-in account: invitation code and link, number of filleuls, tier, and earnings. It lacks an explicit verb like 'retrieve', but the listed fields make the purpose unambiguous. Sibling differentiation is not needed as this is the only referral-related tool.

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?

The description specifies the context: for logged-in users (merchant or individual) with a note that login is requested the first time. However, it does not explicitly state when to use this tool versus alternatives or any exclusions, leaving usage implied rather than clearly guided.

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