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

Annotations already declare readOnly=true, destructive=false and closed-world, so safety is covered. The description adds real behavioral context beyond that: results are stitched across devices/accounts/RevenueCat ids, and the payload includes event breakdown, churn state and recent activity. It omits edge behavior such as not-found handling or any activity-window limits.

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, zero waste: the payload contents are front-loaded and the accepted identifier forms follow. Every clause carries information an agent can act on.

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 a single fully documented parameter, a read-only annotation profile and no output schema, the description carries the needed burden by summarizing the return payload. The remaining gap is edge-case behavior — what is returned when the identifier resolves to nothing or to multiple identities.

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% and the parameter description already says 'Master user id, or any known identifier'. The description adds only the concrete identifier types (device id, account id, RevenueCat id), which is a modest but genuine extension over the schema, so it sits at the baseline rather than above it.

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 names the resource precisely (a single user) and enumerates exactly what comes back: stitched identity across device/account/RevenueCat ids, event breakdown, churn state and recent activity. It does not explicitly contrast with the sibling list_users, but the 'one user's ... full history' framing makes the single-entity scope unmistakable.

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 implied: fetch a full profile for one known user, versus the list_users sibling. There is no explicit when-to-use/when-not statement and no mention of what to do if the user is unknown or ambiguous across identities. The identifier flexibility is guidance about input, not about tool selection.

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