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

Annotations already declare readOnlyHint=false, destructiveHint=false, idempotentHint=false and openWorldHint=true, so the description's job is supplementary. It does add real value: 'WRITE' flags mutation up front, 'changes nothing existing' confirms the operation is purely additive, and 'POST /lists' names the underlying endpoint. It doesn't cover duplicate-name behavior or what happens on failure, but against the annotation baseline this is solid.

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 with the operation mode (WRITE) front-loaded, followed by the effect and the endpoint. Every clause carries information; nothing is padded or repeated.

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 two-parameter, non-nested creation tool this covers the essentials: what it makes, that it is additive, and the HTTP verb/path. Since there is no output schema, a brief hint about what the call returns (e.g., a new campaign identifier) would have closed the last gap.

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 description coverage is 100% and both parameters (name, website) carry their own descriptions with format and length constraints. The description restates them ('name and a default referral URL') without adding syntax or validation detail, so the schema does the heavy lifting and the baseline of 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?

States a specific verb and resource ('create a new ReferralHero campaign') and clarifies the campaign/list terminology, which distinguishes it from list_campaigns and the read-side sibling tools. It stops short of naming an alternative sibling to contrast with, so it is clear but not maximally differentiated.

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?

Usage is only implied by the verb 'create' plus the WRITE marker; there is no explicit when-to-use statement, no prerequisites (e.g., whether the campaign must not already exist), and no pointer to alternatives. An agent can infer the context but must do the work itself.

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