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gmail.users.threads.modify

Adds or removes Gmail label IDs across an entire thread, applying the change to every message in a single request.

Instructions

Modifies the labels applied to the thread. This applies to all messages in the thread. For more information, see Manage threads [HTTP POST] — creates or triggers a change; refused under --readonly safety profiles. Returns the API's response resource as JSON — request body is a JSON ModifyThreadRequest object accepting addLabelIds, removeLabelIds; pass it via params or whole via body_file Siblings over the same resource: delete, get, list, trash, untrash.

Input Schema

Name	Required	Description	Default
`id`	Yes	[URL path segment] The ID of the thread to modify.
`query`	No	Extra KEY=VALUE query pairs for endpoints whose parameters Discovery does not describe.
`params`	No	Parameter map merged into the request; typed parameters win.
`userId`	Yes	[URL path segment] The user's email address. The special value `me` can be used to indicate the authenticated user.	me
`dry_run`	No	Return the request that would be sent, without sending it.
`body_file`	No	Read the request body from this file ('-' for stdin) instead of building one from the parameters. The body is a JSON ModifyThreadRequest object.
`request_body`	No	Request body of type ModifyThreadRequest: pass it via `params` (merged into the built body) or whole via `body_file`.

Output Schema

Name	Required	Description	Default
`id`	No
`snippet`	No
`messages`	No
`historyId`	No

Schema Changelog

Changes observed during successful MCP inspections.

Changed2 schema fields changedOct 26, 2026

changedInput schema / properties / body_file / description

Previous value: -"Read the request body from this file ('-' for stdin) instead of building one from the parameters."New value: +"Read the request body from this file ('-' for stdin) instead of building one from the parameters. The body is a JSON ModifyThreadRequest object."

addedInput schema / properties / request_body

Added value: +{
+  "description": "Request body of type ModifyThreadRequest: pass it via `params` (merged into the built body) or whole via `body_file`.",
+  "properties": {
+    "addLabelIds": {
+      "items": {
+        "type": "string"
+      },
+      "type": "array"
+    },
+    "removeLabelIds": {
+      "items": {
+        "type": "string"
+      },
+      "type": "array"
+    }
+  },
+  "type": "object"
+}

Changed4 schema fields changedOct 26, 2026

changedInput schema / properties / id / description

Previous value: -"The ID of the thread to modify."New value: +"[URL path segment] The ID of the thread to modify."

addedInput schema / properties / userId / default
```
Added value: +"me"
```

changedInput schema / properties / userId / description

Previous value: -"The user's email address. The special value `me` can be used to indicate the authenticated user."New value: +"[URL path segment] The user's email address. The special value `me` can be used to indicate the authenticated user."

changedOutput schema / (root)

Previous value: -nullNew value: +{
+  "properties": {
+    "historyId": {
+      "type": "string"
+    },
+    "id": {
+      "type": "string"
+    },
+    "messages": {
+      "items": {
+        "properties": {
+          "classificationLabelValues": {
+            "items": {
+              "properties": {
+                "fields": {
+                  "items": {
+                    "properties": {
+                      "fieldId": {
+                        "type": "string"
+                      },
+                      "selection": {
+                        "type": "string"
+                      }
+                    },
+                    "type": "object"
+                  },
+                  "type": "array"
+                },
+                "labelId": {
+                  "type": "string"
+                }
+              },
+              "type": "object"
+            },
+            "type": "array"
+          },
+          "historyId": {
+            "type": "string"
+          },
+          "id": {
+            "type": "string"
+          },
+          "internalDate": {
+            "type": "string"
+          },
+          "labelIds": {
+            "items": {
+              "type": "string"
+            },
+            "type": "array"
+          },
+          "payload": {
+            "properties": {
+              "body": {
+                "properties": {
+                  "attachmentId": {
+                    "type": "string"
+                  },
+                  "data": {
+                    "type": "string"
+                  },
+                  "size": {
+                    "type": "integer"
+                  }
+                },
+                "type": "object"
+              },
+              "filename": {
+                "type": "string"
+              },
+              "headers": {
+                "items": {
+                  "properties": {
+                    "name": {
+                      "type": "string"
+                    },
+                    "value": {
+                      "type": "string"
+                    }
+                  },
+                  "type": "object"
+                },
+                "type": "array"
+              },
+              "mimeType": {
+                "type": "string"
+              },
+              "partId": {
+                "type": "string"
+              },
+              "parts": {
+                "items": {
+                  "properties": {
+                    "body": {
+                      "type": "object"
+                    },
+                    "filename": {
+                      "type": "string"
+                    },
+                    "headers": {
+                      "items": {
+                        "type": "object"
+                      },
+                      "type": "array"
+                    },
+                    "mimeType": {
+                      "type": "string"
+                    },
+                    "partId": {
+                      "type": "string"
+                    },
+                    "parts": {
+                      "items": {
+                        "type": "object"
+                      },
+                      "type": "array"
+                    }
+                  },
+                  "type": "object"
+                },
+                "type": "array"
+              }
+            },
+            "type": "object"
+          },
+          "raw": {
+            "type": "string"
+          },
+          "sizeEstimate": {
+            "type": "integer"
+          },
+          "snippet": {
+            "type": "string"
+          },
+          "threadId": {
+            "type": "string"
+          }
+        },
+        "type": "object"
+      },
+      "type": "array"
+    },
+    "snippet": {
+      "type": "string"
+    }
+  },
+  "type": "object"
+}

First observedOct 26, 2026

TDQS

A3.9/5.0

Behavior4/5

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

With no annotations, the description carries the full behavioral burden and does well: it discloses that this is a mutation, that it affects every message in the thread, that it is refused under readonly safety profiles, and that it returns the API response resource as JSON. It does not mention required OAuth scopes or error conditions, but the key mutation and safety behavior is disclosed.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is front-loaded with the core purpose and scope, then adds mutation, return, request-body, and sibling information. It is somewhat dense and includes a documentation link and sibling list, but those details are relevant rather than filler.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

The tool has an output schema, full parameter description coverage, and a clear mutation-oriented description. Given that structured data already covers parameters and return shape, the description is complete enough for correct invocation, with only auth/scope details missing.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so the parameters are already well documented by the schema itself. The description adds some useful framing by naming ModifyThreadRequest and its addLabelIds/removeLabelIds fields and by explaining that the body can be passed via params or body_file, but this largely restates schema-provided information.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description states a specific verb and resource: it modifies labels applied to a thread, and explicitly notes that this applies to all messages in the thread. That scope statement distinguishes it clearly from message-level modification and from the listed thread siblings.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines3/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description names sibling operations over the same resource, which gives some orientation, but it does not explain when to choose thread modification versus message modification or batchModify. Usage is implied by the verb and scope, not explicitly guided.

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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