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

Goes beyond the annotations by stating the permission requirement and the storage footprint ('Stores only the domain and two labels'), which is the kind of scope detail annotations cannot convey. 'Calling again replaces the mapping' restates the idempotentHint in operational terms and clarifies that no duplicates accumulate. It stops short of describing the response, but the write/idempotent/non-destructive profile is fully covered.

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 compact sentences with zero filler, front-loading the audience restriction before the action. Every clause (audience, action, storage, replace semantics) carries distinct information.

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 three-parameter write tool with no output schema and annotations covering safety and idempotency, the description supplies the key extras: who may call it and what state it mutates. The only gap is that it does not explain the effect of the mapping on downstream acquisition reporting, which would help an agent set expectations.

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%, so each parameter (domain hostname, source label, channel label) is already documented with examples. The description adds only the aggregate observation that all three values are persisted, which is marginal beyond the schema. Baseline 3 applies when the schema does the heavy lifting.

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: map an external referrer domain to a source and channel in the acquisition view. The three arguments are named inline, so an agent knows exactly what the tool operates on. Nothing in the sibling list (catch_up, claim, export, etc.) competes with this function.

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?

Gives a clear precondition ('Product administrators only') and a trigger ('when an administrator asks'), which is the relevant context for a privileged admin configuration tool. It names no alternative tool or exclusion, but no sibling performs comparable mapping, so the omission is minor.

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