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

Annotations already declare destructiveHint=true, idempotentHint=false, and openWorldHint=true, so the safety profile is covered. The description still adds real behavior beyond that: that a sent email cannot be recalled (confirming irreversibility) and that a duplicate forward within 24h is delivered only once — a non-obvious delivery rule. The 24h de-dup note reads slightly at odds with idempotentHint=false but refers to delivery de-duplication rather than tool call semantics, so it is not a contradiction.

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 tight sentences with the action front-loaded and no filler; the composition detail and delivery rule each carry weight. Slight density from semicolon-chained clauses, but nothing is wasted.

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 6-parameter, nested-body mutation tool with no output schema, the description covers the action, the quoting behavior, irreversibility, and duplicate-delivery handling. It does not address the cc/bcc dimensions or confirm what the call returns, leaving small gaps.

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 coverage is 50% (id, body, subject are documented; to, cc, bcc are not). The description corroborates "recipients" (to) and an "optional note" (body), but adds no syntax, limits, or explanation for cc/bcc or the subject override — which the schema does partially cover for subject. Baseline 3 is appropriate given the mixed coverage.

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 ("Forward an email to the given recipients, from the mailbox that owns it") and clarifies the composition shape (original quoted below an optional note). It is distinguishable from reply_to_email by the word "forward", though it never names or contrasts that sibling 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?

Usage is implied: this is the tool for forwarding an existing message identified by id. There is no explicit when-to-use/when-not guidance and no mention of the obvious alternative (reply_to_email) or when forwarding is preferable to replying.

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