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

Annotations already declare readOnlyHint/destructiveHint=false, so the description correctly spends its words elsewhere: it discloses the 102 KB Gmail clip point, the Word-engine Outlook constraint, and crucially that the embedded support notes are dated 2026-10 and may have drifted. That caveat materially changes how an agent should present results, though it says nothing about output shape or whether it reports pass/fail per check.

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 purpose is front-loaded, but the check list is one ~150-word run-on joined by commas that is hard to scan and mixes scope with rationale and caveats. It earns most of its length for selection purposes, but bullets or a shorter summary plus link to details would be stronger.

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, read-only tool with no output schema, the description covers scope, the standards it judges against, and the trustworthiness of those standards. The remaining gap is what a result looks like (issue list? counts?), which an agent must guess before summarizing to a user.

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?

One required parameter at 100% schema coverage, so the baseline is 4. The description's 'pasted email HTML' reinforces that the value is raw source rather than a URL or rendered page, which is a useful disambiguation given sibling tools operate on URLs.

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: 'Lint pasted email HTML', and the enumerated checks make the scope concrete (client-compat/rendering lint, not accessibility or copy). It does not name which siblings (check_email_accessibility, check_email_dark_mode, check_email_preheader) it supersedes or complements, so differentiation is left to inference.

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?

'Pasted' implies the input is raw HTML source, and the closing sentence gives a verification step ('confirm in real clients') after use. But there is no explicit statement of when to choose this over the many overlapping email siblings, and no exclusions or prerequisites.

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