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

Annotations declare readOnlyHint=true, which establishes safety. The description adds 'Public and keyless' (authentication requirements) and 'live count' (real-time behavior), which are useful behavioral traits beyond the annotation. This adds context about access and data freshness without contradicting the annotation.

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?

The description is two sentences long, front-loads the core concept ('rolling 24-hour aggregate rollup'), and provides a list of example metrics. It avoids redundancy and keeps the text tight, though 'tape legs' could be more explicit, it does not detract from conciseness.

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?

The tool is simple (no parameters, no output schema), and the description covers the main return content: named categories with counts and the live count aspect. It doesn't detail the exact response format, but given the simplicity, the description is sufficiently complete for an agent to understand what the tool returns.

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?

The tool has zero parameters, and the schema is empty. The baseline for 0 parameters is 4, and the description correctly avoids inventing parameters. No additional parameter semantics are needed.

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 clearly identifies the tool as a rolling 24-hour aggregate rollup with specific metrics (DNS provider changes, CA switches, mail moves, unreachable domains). It conveys the resource and what counts are provided, but it does not explicitly differentiate from the sibling tool 'whats_changed_today', so it doesn't fully distinguish from alternatives.

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 description includes 'Public and keyless', indicating that no authentication is required, which is a prerequisite. However, it provides no guidance on when to use this tool versus sibling tools like 'whats_changed_today' or 'lookup_domain'. There is no mention of exclusions or alternative scenarios, so usage guidance is minimal.

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