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

Goes well beyond the readOnly/non-destructive annotations by disclosing the security model: passwords never pass through the AI and Thunderbird's saved passwords are never read, plus the exact remediation path (user types the password into Local MCP's settings window) and the provider sign-in limitation requiring an app password. These are precisely the facts an agent needs to explain a needs_password result to a user.

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?

Purpose and status enum are front-loaded in the first sentence, with remediation detail following. Three sentences with no filler, though the middle sentence is dense and runs the setup flow and the no-password-passthrough guarantee together.

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?

An output schema exists, so return values need no explanation; what remains — what each status means, why an account might be unsupported, and how a user fixes it — is fully covered. Nothing an agent needs to interpret or act on the result 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 the single optional 'profile' parameter is documented there, so the schema carries the burden. The description never mentions profile selection or what happens with multiple profiles, adding no meaning beyond the schema — 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?

States a specific verb (reports) and a precisely scoped resource: per-account send capability, with the three possible outcomes enumerated (ready, needs_password, not_supported plus reason). That specificity makes it hard to confuse with thunderbird_list_accounts or thunderbird_send_email, though no sibling is named explicitly.

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?

Gives clear context for when this matters (before attempting to send) and an explicit exclusion — "Reading mail needs none of this" — which tells the agent this check is irrelevant for read workflows. It stops short of naming a concrete alternative or pre-send sequencing (e.g. 'call before thunderbird_send_email').

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