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

Annotations already establish readOnlyHint=true and destructiveHint=false, and the description adds non-obvious behavior: the 5-minute active window, unique-visitor dedup semantics, and the exact JSON shape returned. It does not cover error behavior or rate limits, but those risks are low for a read-only counter.

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 short sentences, no filler, and the core scope is front-loaded. The return-value example is compact and earns its place because there is no output schema.

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 a one-optional-parameter read-only tool, it covers the safety profile via annotations, the return contract via the example, and counting semantics via the 5-minute window. The only notable absence is routing guidance to sibling analytics tools, which is already reflected in the usage-guidelines score.

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% and the single optional site parameter is already documented thoroughly. The tool description adds almost nothing about parameter formatting, but per the baseline this is acceptable because the schema carries the full burden.

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 opens with a specific verb and resource: 'Realtime count of unique visitors active in the last 5 minutes for a site.' This clearly scopes the tool to current active visitors and, with the return shape, distinguishes it from siblings like visitors_over_time and query_stats.

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?

The realtime and 5-minute wording implies this is for current-count use cases, but the description never states when to prefer it over visitors_over_time or query_stats, nor gives exclusions. The optional-site semantics are left to the schema rather than explained as usage guidance.

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