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

Beyond the annotations, the description discloses the duplicate case (nothing changes, already_key_event true, existing key event returned) and explicitly bounds the blast radius: nothing is changed in Google Ads, which must be imported separately. There is mild tension with idempotentHint=false, since the described duplicate behavior is effectively a no-op, but the annotations are conservative for a create-style call and the description clarifies real semantics rather than contradicting them.

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-loaded with the action, then the duplicate-case caveat, then the cross-product boundary — a sensible order with no filler prose. The trailing 'Tools revision: d80f65c0' is metadata noise that does not help an agent select or call the tool.

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?

An output schema exists, so return values like already_key_event need not be explained, and the description does cover the key behavioral edge case and the Google Ads boundary. What is missing is any parameter-level guidance for a two-parameter mutation with zero schema descriptions, plus explicit sibling routing against ga4_update_conversion_event.

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 0% and the description says nothing about either parameter. It never indicates that property takes a GA4 property identifier (e.g. properties/123456789) or what form event_name must take, so an agent must guess the identifier format for a mutation that is hard to undo.

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 first sentence gives a specific verb and resource: mark an event as a conversion (key event) on a GA4 property. That is unambiguous on its own. It does not, however, distinguish itself from nearby siblings such as ga4_update_conversion_event or create_conversion_action, so the agent has to infer that this one is the create/attach path rather than the edit path.

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 rather than stated: the duplicate-handling paragraph tells the agent this is the safe call when unsure whether the event is already a key event, which is genuinely useful guidance. There is no explicit when-not or named alternative (e.g. use ga4_update_conversion_event to change an existing key event's settings), so the agent must infer routing.

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