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

Annotations already cover read-only, idempotent, non-destructive and open-world, so the safety profile is pre-declared. The description goes beyond that with operational context the annotations cannot carry: 'No auth, ~3-8s' and the fact that it returns an aggregated 0-100 score with a prioritised issue list. It stops short of failure modes or partial-check behaviour, keeping it at 4 rather than 5.

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?

Four dense sentences, front-loaded with the composite scope, then the sibling-routing rules, then latency/auth. Every clause carries information the agent needs; nothing is padded or repeated from the 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?

No output schema exists, but the description still tells the agent what comes back (aggregated 0-100 score, prioritised issue list) in addition to what is checked, how long it takes, and that no auth is required. For a one-parameter read-only aggregate tool, nothing material is missing.

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 there is a single required 'domain' parameter with a clear format note (no URL/path/port). The description adds no parameter-level detail beyond what the schema already provides, so the baseline 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?

Opens with a specific verb+resource ('Read-only combined email-security check') and then enumerates exactly what is covered: SPF parse, DKIM selector discovery, DMARC policy validation, MX blacklist status, and an aggregated score. This is unmistakably distinct from the granular check_spf / discover_dkim / check_dmarc siblings named in the same sentence.

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?

Explicitly states both when to use it ('one-shot email security overview', 'replaces sequential check_spf + discover_dkim + check_dmarc + check_blacklist for the typical case') and when not to ('use check_sender_requirements specifically for Google/Yahoo bulk-sender compliance, or the individual check_* tools when you need only one signal'). The routing decision is fully resolved for the agent.

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