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

Annotations already declare read-only, closed-world safety, so the description adds meaningful extra context: default retention semantics, the mode switch, and that anonymous access is confined to synthetic read-only demo data with sign-in required for real projects. It omits output shape and performance notes, but adds real value beyond the 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?

Three short sentences, front-loaded with the core purpose, then default behavior, then the auth/preview caveat. Every sentence carries information; no filler.

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?

With no output schema, the description does not need to explain return values, and annotations cover the safety profile. It addresses defaults, mode switching, and access constraints, leaving only minor gaps such as pagination or result formatting for a 5-param read tool.

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 coverage is 100%, including descriptions for event, period, cohorts, project, and returning_event, so the schema carries the parameter burden. The description only reinforces the event parameter's mode-switching effect, adding marginal value above the schema, which is the expected baseline of 3.

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 ('Cohort retention analysis — track what % of users return over time'), which clearly distinguishes it from siblings like analytics_funnel, analytics_breakdown, or analytics_paths. An agent can identify the analysis type without opening the schema.

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?

Explains the default mode (session-based retention) and the condition that switches behavior ('Pass event to switch to event-based retention'), plus the anonymous-preview restriction. It does not name an alternative sibling to use instead when retention isn't the right analysis, so it falls short of a 5.

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