list_labels

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

Annotations already declare readOnlyHint=true, and the description does not contradict this. It adds behavioral context by explaining auto-detection among ProtonMail, Gmail, and IMAP label systems, and discloses the ProtonMail folder prefix behavior. This goes beyond the annotation and helps the agent understand potential platform-specific variations.

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 concise but complete, with four short sentences. The first sentence front-loads the core purpose, followed by essential auto-detection details and a practical ProtonMail tip. Every sentence earns its place with no redundancy or 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?

Given the simple one-parameter tool with no output schema, the description covers the key behaviors: what it lists, how it auto-detects, and a platform-specific note. It does not detail the exact return format, but for a straightforward list operation this is acceptable. It could be slightly more explicit about output, but overall it is sufficiently complete.

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 description coverage is 100% (the 'account' parameter is described as 'Account name from list_accounts'). The tool description does not add further meaning to the parameter; it relies on the schema. According to the rubric, a baseline of 3 is appropriate when the schema fully documents parameters.

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 clearly states the tool's purpose: 'List available labels for an email account.' It uses a specific verb ('list') and resource ('labels'), and distinguishes itself from sibling tools like list_mailboxes by focusing on the label system and auto-detection. The ProtonMail note further differentiates this from generic mailbox listing.

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 context on when to use the tool and how to handle ProtonMail-specific label representation. It explicitly instructs using list_emails with a specific mailbox prefix to find emails with a ProtonMail label. However, it does not explicitly exclude alternatives like list_mailboxes or state when not to use this tool, so it stops short of a full when/when-not guide.

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