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

Annotations already declare readOnlyHint, destructiveHint=false and openWorldHint=false, so safety is covered. The description adds genuinely new behavioral context: the data comes from an in-memory ring buffer and issues no D1 query, which tells the agent the call is cheap, non-persistent, and bounded in history. It stops short of stating retention limits or latency figures.

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, both front-loaded: the payload is listed first, then the implementation detail that determines cost. No filler, no restatement of the tool name.

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?

There is no output schema, but the description compensates by enumerating the returned fields, which is the most important missing piece for this tool. Combined with annotations covering the safety profile and a fully documented schema, an agent has nearly everything needed; only retention/refresh semantics of the ring buffer are unstated.

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% — both 'window' (10-300s, default 60) and 'project' are documented inline. The description adds no further parameter meaning (e.g. how 'window' interacts with the 'events per minute' figure), so the baseline of 3 applies.

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?

Names a specific artifact ('Real-time snapshot') and enumerates exactly what it contains: active visitors, sessions, events per minute, top pages, recent events. That is far more specific than sibling names like analytics_overview or sessions, though it never explicitly contrasts itself with those siblings.

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 only implied: the word 'Real-time' plus the 'no D1 query' note signal that this is for live monitoring rather than historical analysis, but there is no explicit when-to-use/when-not statement and no named alternative (e.g. analytics_overview, query).

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