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

Annotations already establish the safe read-only/idempotent profile, so the bar is lower. The description adds genuine value beyond that: it warns that aiReferral.undercountNote means the AI-referral figure is a floor, never a complete count, which is important interpretation context an agent cannot get from the schema or annotations.

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?

Front-loads the core purpose in the first clause, then spends the remainder on the AI-referral interpretation caveat. The 'not decoration' phrasing is slightly editorial but the sentences are otherwise substantive and non-redundant.

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 read-only analytics tool with full schema coverage and no output schema, the description covers purpose plus the one non-obvious interpretation trap (undercounting AI referrals). It never enumerates the referrer/channel/UTM output fields, but the schema and the sibling set make the shape inferable.

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 projectId, startDate, endDate, and referrerLimit are all documented in the schema. The description adds nothing about parameter syntax or defaults, so baseline 3 is appropriate.

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+resource (referrer/channel/UTM breakdown) and scopes it to 'a project's own tracking snippet,' which distinguishes it from the GA4 siblings. It does not explicitly name which sibling to prefer, but the first-party vs third-party framing makes the boundary reasonably clear.

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?

No explicit when-to-use/when-not guidance or named alternative. The 'FREE, first-party' note implies a reason to choose this over GA4 channel breakdowns, but the agent must infer that routing decision rather than being told.

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