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

With no annotations, the description carries the burden and does so well: it discloses the verdict taxonomy (verified/unverified/suspicious), clarifies that SPF/DKIM/DMARC are 'recorded by the receiving provider' rather than independently re-checked, and states 'Nothing is stored,' covering the privacy/retention question. It omits failure behavior on malformed headers and any rate-limit or auth notes, which keeps it from a 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?

Front-loaded with the decision question followed by input instructions, then the return contents, so the reader gets the essentials first. The long enumeration of returned fields is justified because no output schema exists, though it is a single dense sentence that could be broken into a short list for faster scanning.

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-parameter tool with no output schema and no annotations, everything needed to call it correctly is present: what input to supply, where to get it, what the response contains, the verdict categories, and the no-storage guarantee. 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?

There is a single required parameter fully documented by the schema (raw header text), so the schema baseline applies. The description adds real value beyond the schema by explaining where users obtain raw headers in Gmail and Outlook and that the whole raw block (not just From) is expected. No format or size limits are given.

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 concrete question and a specific verb+resource: analyze raw email headers to judge authenticity, then enumerates exactly what is produced (sender identity, SPF/DKIM/DMARC, look-alike names, Received hops, sending IP, verdict). An agent can immediately tell this is a header forensics tool rather than a DNS or IP tool. It does not explicitly name the neighboring email-related tool (check_email_security), so sibling differentiation is left implicit through the raw-header input requirement.

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?

It gives clear usage context ('Is this email real or fake?') and practical acquisition instructions (Gmail Show original, Outlook View message details), which is exactly the context an agent needs to gather the input. There is no explicit 'when not to use' or named alternative for domain-level checks, so it stops short of full routing guidance.

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