list_unsubscribe

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

Annotations already declare readOnlyHint=true, and the description strongly reinforces this with 'without contacting anyone' and 'SIDE EFFECTS: none — no request is made to the sender.' It also discloses important nuances: it reads the newest message carrying the header, bodyCandidates come from untrusted message text, and they must not be treated as an actual opt-out. This goes well beyond the annotations.

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 description is long but every major section earns its place: field meanings, safety warnings, use cases, and side effects. It is front-loaded with the core purpose before diving into details. There is minor redundancy between 'without contacting anyone' and 'SIDE EFFECTS: none,' but overall the length is justified by the nuanced output behavior.

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?

The description covers the tool's purpose, when to use it, how it behaves regarding headers and body text, safety constraints, side effects, and relationships to sibling tools. It also explains the special cases of `hasUnsubscribe`, `bodyCandidates`, and untrusted content. Given the output schema exists, no important gap remains for an agent to invoke this tool correctly.

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?

The schema only defines `threadId` as a required string with no description, so the description carries the burden. It adds meaning by explaining that the tool operates on a thread and reads the newest message in that thread, even noting how a reply threaded onto a newsletter is handled. This gives enough context for an agent to understand what `threadId` represents, though no explicit format guidance is provided.

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?

The description opens with a specific verb and resource: 'Report the opt-out options a thread advertises (List-Unsubscribe / RFC 8058), without contacting anyone.' It clarifies this is a read-only inspection tool and distinguishes it from the sibling `unsubscribe` tool by explicitly noting that `unsubscribe` can perform the one-click opt-out.

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?

The description provides an explicit 'USE WHEN' section: 'checking whether a newsletter can be unsubscribed from, or showing the user the link to click.' It also gives alternative routing by pointing to the `unsubscribe` tool for oneClick cases and instructs the agent to never fetch bodyCandidates, establishing clear boundaries for safe use.

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