labels_listList the labels a connected mailbox holds, by the id each is applied by. A mailbox whose provider is imap holds its folders as labels, nested by /, beside UNREAD, STARRED and SPAM.
| Name | Required | Description | Default |
|---|---|---|---|
| mailbox | Yes | The mailbox's name or its email address. |
| Name | Required | Description | Default |
|---|---|---|---|
| labels | Yes |
Changes observed during successful MCP inspections.
Input schema / $schemaPrevious value: -"http://json-schema.org/draft-07/schema#"New value: +"https://json-schema.org/draft/2020-12/schema"Output schema / $schemaPrevious value: -"http://json-schema.org/draft-07/schema#"New value: +"https://json-schema.org/draft/2020-12/schema"Output schema / properties / labels / items / properties / type / anyOfRemoved value: -[
- {
- "type": "string"
- },
- {
- "type": "null"
- }
-]Output schema / properties / labels / items / properties / type / typeAdded value: +[
+ "string",
+ "null"
+]Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already establish readOnlyHint=true and destructiveHint=false, so safety is covered. The description adds genuine behavioral context beyond that: that IMAP folders surface as labels nested by '/', and that system labels UNREAD, STARRED and SPAM are always present.
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?
Two compact sentences with the core purpose front-loaded and the IMAP caveat second. The phrase 'by the id each is applied by' is slightly awkward and costs a little readability, 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?
An output schema exists, so return-value explanation is not needed, and the description covers the non-obvious IMAP label semantics. For a one-parameter read tool with full schema coverage and annotations, this is sufficient.
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% and the single 'mailbox' parameter is fully documented as a name or email address, so the schema carries the parameter burden. The description adds no format or syntax detail about the identifier beyond what the schema already states.
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 states a specific verb and resource ('List the labels a connected mailbox holds') and adds a scoping detail about IMAP providers that separates it from the mailboxes_list sibling. It stops short of explicitly naming the sibling it is not, so it is clear but not fully differentiated.
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?
Usage is only implied by the mention of a connected mailbox and the IMAP folder-as-label note. There is no explicit statement of when to call labels_list versus mailboxes_list, nor any prerequisite or exclusion.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
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