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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint=false, so the safety profile is covered. The description adds genuinely new behavioral context beyond them: that analysis is performed in memory and headers are not stored, which matters for handling sensitive message data. It stops short of covering failure behavior (malformed headers, size limits) or return format.

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 dense sentences, zero padding, with the core capability front-loaded and the privacy/retention note as a closing qualifier. Every clause carries information an agent can act on.

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 single-parameter, no-output-schema tool the description does the necessary work by enumerating what the analysis yields (hops, delays, authentication results, spam findings), and annotations cover safety. Only minor gaps remain: no mention of limits on malformed or truncated headers, and no hint of how results are structured.

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%, so the single 'headers' parameter is already fully documented including format guidance and the note that the body is ignored. The description reinforces that the input is raw headers and hints at what gets derived from them, but adds no syntax or format detail beyond the schema; the baseline of 3 is appropriate.

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?

States a specific verb and resource ('Reads the raw headers of an email') and enumerates the scope it covers: hop-by-hop delivery path with delays, SPF/DKIM/DMARC results, spam headers and findings. It does not explicitly distinguish itself from siblings like spf_check, dkim_check or dmarc_check (which operate on DNS records rather than a message), so an agent must infer the distinction.

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 when-to-use or when-not-to-use guidance and no alternative tool is named, even though the sibling set contains three closely related authentication checkers. The only contextual cue ('as shown by Show original or View message source') lives in the schema, not the description, so the description itself offers no routing guidance.

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