List labels

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

Beyond the readOnlyHint annotation it discloses real behavior: automatic detection of the label backend (ProtonMail folder-labels, Gmail X-GM-LABELS, IMAP keywords) and the ProtonMail folder-label representation. It omits pagination and return shape, but adds meaningful context that annotations do not cover.

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?

Four short sentences, front-loaded with the core action, then backend behavior, then the ProtonMail caveat and the routing hint. No filler sentences.

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 read-only single-param list tool with no output schema, the description covers purpose, backend variance, and the ProtonMail edge case that would otherwise trip an agent. It stops short of describing what the returned entries look like, the only notable gap.

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 a single 'account' parameter already described as coming from list_accounts; the description only alludes to 'an email account' and adds no syntax or format detail beyond the schema. 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?

Specific verb+resource ('List available labels for an email account') with the scope narrowed by naming the three label systems it handles. It also distinguishes itself from folder-oriented siblings by noting that ProtonMail labels surface as IMAP folders under Labels/.

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 concrete follow-up usage: pair the result with list_emails and mailbox="Labels/<name>", which is exactly the workflow an agent needs. It does not explicitly say when to prefer list_mailboxes or list_labels, so no full when-not guidance.

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