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

Goes well beyond the annotations: "Sends nothing", opens a new thread, closes the original, and enumerates refusal cases (loop, repeat, opted-out, bounced, chain deeper than three). This confirms and elaborates the destructiveHint=true / non-idempotent profile rather than contradicting it.

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-loads the counterintuitive fact ("Sends nothing") before the mechanics, and each sentence carries distinct information. Slightly dense and could be split, but there is no filler.

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 non-idempotent mutating tool with full schema coverage and no output schema, the description covers side effects, refusal conditions, and the reply-routing caveat. What happens on a refused redirect (error surface) is the only notable omission.

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 100% with self-documenting field descriptions (name, email, conversationId with provenance from list_inbox/get_thread). The description refers to "that address" and the referral context but adds no syntax or format detail beyond the schema, so the baseline of 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?

Specific verb (redirect/hand off) plus resource (thread), with a concrete mechanism: opens a NEW thread to the named address, carries the referral, closes the original as redirected. An agent can distinguish this from send_reply and archive_thread purely from the description.

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?

States the triggering condition explicitly ("somebody replies 'I am not the right person, talk to X'") and pre-empts the obvious confusion by noting send_reply still answers the original referrer. When-to-use and the relevant alternative are both named.

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