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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive), and the description still adds real behavioral context the annotations cannot: realtime figures are preliminary, never cached, standard properties cover 30 minutes versus 60 for GA4 360. Those freshness and coverage constraints directly affect how an agent should interpret results.

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?

It is a single dense paragraph rather than a list, but each clause earns its place: trigger, window, dimensions, metrics, tier differences, freshness, and safety. The trigger is front-loaded so the first sentence carries the routing decision.

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 an 8-parameter tool with nested filters, an output schema is present so return values need not be explained, and the schema covers most parameters. The description supplies the realtime-specific context (window length, preliminary data, default metric) and is close to complete, only omitting guidance on filter/metric combinations that the schema partly covers.

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 88%, so the schema already documents filters, metrics, dimensions, row_limit and minutes_ago in detail. The description restates the default metric and a few dimension names ('unifiedScreenName', event name) that are already in the schema, adding little beyond the baseline.

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 ('Run a Google Analytics realtime report') and immediately pins the scope to 'right now: active users in the last 30 minutes'. That realtime framing is exactly what distinguishes it from the sibling run_report, so an agent can choose correctly 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?

Gives a concrete trigger: 'Use this when the user asks what is happening on their site or app right now'. It implies the split from historical reporting but never names run_report as the alternative or states the when-not condition explicitly, 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.