mail_thread

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

Annotations only cover safety (readOnly, non-destructive); the description adds substantial context beyond them: dedupe behavior, truncation direction (oldest dropped) and its `truncated` signal, empty results for unknown ids, snippet read off disk with no Mail launch, and the Full Disk Access prerequisite. It even specifies that an unreadable body yields an absent `snippet` key rather than an empty one.

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-loaded with the core purpose and structured around the snippets decision, so it reads well. Minor redundancy — 'no Mail launch' is asserted twice ('no Mail launch and no extra calls' and 'Fast, read-only, no Mail launch') — keeps it just short of a 5.

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 3-parameter read tool with an output schema, the description covers everything an agent needs: return shape, truncation direction, unknown-id behavior, snippet opt-in cost, and the FDA permission requirement. Nothing material is left to inference.

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 0%, so the description must carry the load — and it does: `id` identifies the conversation, `limit` controls truncation with the oldest messages dropped when exceeded, and `snippets=True` toggles a ~200-char body preview with explicit absent-key semantics. All three parameters gain meaning beyond their bare types.

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: every message in the conversation containing `id`, oldest-first, including messages the user sent, with dedupe across mailboxes. An agent can immediately distinguish this from mail_bodies, mail_body, or mail_search without opening a schema.

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?

Explicitly routes the agent: use `snippets=True` to see who spoke last, then `mail_bodies(ids)` for the few worth hydrating; leave snippets off for a long thread you only need to enumerate. Both the when and the when-not are stated alongside the named alternative.

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