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

Annotations already declare readOnly, idempotent, openWorld and non-destructive, so the safety profile is covered. The description still adds useful behavioral context by disclosing the scope of analysis (live MX records and Workspace/M365 detection), which explains why openWorldHint is set; it does not mention rate limits or lookup latency.

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?

One front-loaded sentence led by the verb, with the outputs packed into a clean list. No filler, no restatement of the title or 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?

With no output schema, the description correctly carries the return-value burden and enumerates what comes back (category, mail provider, MX, Workspace/M365). The main gap is the 'policy' parameter's effect on the result, which neither the description nor an output schema clarifies.

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%, with both 'domain' and the 'policy' enum fully documented in the schema, so the baseline is 3. The description repeats the acme.io example but adds nothing about how policy values change the verdict, leaving that entirely to the schema.

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?

Uses a specific verb ('Classify') on a specific resource ('a domain') and enumerates the classification buckets plus derived signals (mail provider, MX records, Workspace/M365). It is clearly domain-scoped, which inherently separates it from check_email and check_batch, but it never names those siblings to make the boundary explicit.

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?

There is no statement of when to reach for this tool versus check_email or check_batch, and no prerequisites or exclusions. The only usage hint is the 'policy' enum's reference to 'the recommendation', which is incidental rather than real guidance.

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