add_labelsAdd labels, or Outlook categories, to messages.
| Name | Required | Description | Default |
|---|---|---|---|
| labels | Yes | Gmail labels or Outlook categories | |
| accountId | No | Account to operate on. Optional when exactly one account is connected. | |
| messageIds | Yes | Messages to change, up to 100 IDs |
| Name | Required | Description | Default |
|---|---|---|---|
| data | Yes |
Changes observed during successful MCP inspections.
Output schema / (root)Previous value: -nullNew value: +{
+ "additionalProperties": false,
+ "properties": {
+ "data": {
+ "additionalProperties": true,
+ "properties": {
+ "action": {
+ "type": "string"
+ },
+ "failed": {
+ "items": {
+ "additionalProperties": false,
+ "properties": {
+ "code": {
+ "type": "string"
+ },
+ "messageId": {
+ "type": "string"
+ }
+ },
+ "required": [
+ "messageId",
+ "code"
+ ],
+ "type": "object"
+ },
+ "type": "array"
+ },
+ "succeededIds": {
+ "items": {
+ "type": "string"
+ },
+ "type": "array"
+ },
+ "uncertainIds": {
+ "items": {
+ "type": "string"
+ },
+ "type": "array"
+ }
+ },
+ "required": [
+ "action",
+ "succeededIds",
+ "failed",
+ "uncertainIds"
+ ],
+ "type": "object"
+ }
+ },
+ "required": [
+ "data"
+ ],
+ "type": "object"
+}Input schema / properties / accountId / anyOfPrevious value: -[
- {
- "minLength": 1,
- "type": "string"
- },
- {
- "type": "null"
- }
-]New value: +[
+ {
+ "maxLength": 512,
+ "minLength": 1,
+ "type": "string"
+ },
+ {
+ "type": "null"
+ }
+]Input schema / properties / labels / items / maxLengthAdded value: +512Input schema / properties / messageIds / descriptionPrevious value: -"Messages to change, up to 100 distinct IDs"New value: +"Messages to change, up to 100 IDs"Input schema / properties / messageIds / items / maxLengthAdded value: +512Input schema / properties / messageIds / maxItemsAdded value: +100Input schema / $schemaPrevious value: -"https://json-schema.org/draft/2020-12/schema"New value: +"http://json-schema.org/draft-07/schema#"Input schema / properties / accountId / anyOfAdded value: +[
+ {
+ "minLength": 1,
+ "type": "string"
+ },
+ {
+ "type": "null"
+ }
+]Input schema / properties / accountId / descriptionAdded value: +"Account to operate on. Optional when exactly one account is connected."Input schema / properties / accountId / maxLengthRemoved value: -512Input schema / properties / accountId / minLengthRemoved value: -1Input schema / properties / accountId / typeRemoved value: -"string"Input schema / properties / labels / descriptionAdded value: +"Gmail labels or Outlook categories"Input schema / properties / labels / items / maxLengthRemoved value: -512Input schema / properties / messageIds / descriptionAdded value: +"Messages to change, up to 100 distinct IDs"Input schema / properties / messageIds / items / maxLengthRemoved value: -512Input schema / properties / messageIds / maxItemsRemoved value: -100Input schema / $schemaPrevious value: -"http://json-schema.org/draft-07/schema#"New value: +"https://json-schema.org/draft/2020-12/schema"Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare the safety profile (readOnlyHint=false, idempotentHint=true, destructiveHint=false), so the description only needs to fill in the gaps. It adds the useful cross-provider synonym (Outlook categories) but says nothing about whether labels must already exist, whether additions are additive-only, or what happens on an already-labeled message.
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?
A single front-loaded sentence with no filler; the verb and resource lead. It is arguably under-specified rather than over-long, so nothing needs to be cut.
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?
With a full output schema, full parameter coverage, and a complete annotation set, most of the burden is already carried elsewhere. However, for a label-mutating tool the description omits whether labels are auto-created or must pre-exist, which is the one thing an agent could easily get wrong.
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%, with labels, messageIds, and accountId all documented, so the baseline is 3. The description's only addition is clarifying that 'labels' also means Outlook categories, which is mildly useful but largely redundant with the schema's own wording.
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 (add) and resource (labels/categories) plus the target object (messages), so the operation is unambiguous. It does not explicitly contrast with the sibling remove_labels, but the add/remove pairing in the tool names makes the split obvious.
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?
No guidance on when to use this versus alternatives such as move_emails, archive_emails, or remove_labels, and no prerequisites noted. The agent must infer usage entirely from the verb.
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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