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chat.spaces.messages.reactions.create

Creates an emoji reaction on a Google Chat message so users can respond directly to specific message content.

Instructions

Creates a reaction and adds it to a message. For an example, see Add a reaction to a message. Requires user authentication with one of the following authorization scopes: - https://www.googleapis.com/auth/chat.messages.reactions.create - https://www.googleapis.com/auth/chat.messages.reactions - https://www.googleapis.com/auth/chat.messages - https://www.goog [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 Reaction object accepting emoji, name, user; pass it via paramsor whole viabody_file` Siblings over the same resource: delete, list.

Input Schema

Name	Required	Description
`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.
`parent`	Yes	[URL path segment] Required. The message where the reaction is created. Format: `spaces/{space}/messages/{message}`
`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 Reaction object.
`request_body`	No	Request body of type Reaction: pass it via `params` (merged into the built body) or whole via `body_file`.

Output Schema

Name	Required	Description	Default
`name`	No
`user`	No
`emoji`	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 Reaction object."

addedInput schema / properties / request_body

Added value: +{
+  "description": "Request body of type Reaction: pass it via `params` (merged into the built body) or whole via `body_file`.",
+  "properties": {
+    "emoji": {
+      "properties": {
+        "customEmoji": {
+          "properties": {
+            "emojiName": {
+              "type": "string"
+            },
+            "name": {
+              "type": "string"
+            },
+            "payload": {
+              "properties": {
+                "fileContent": {
+                  "type": "string"
+                },
+                "filename": {
+                  "type": "string"
+                }
+              },
+              "type": "object"
+            },
+            "temporaryImageUri": {
+              "type": "string"
+            },
+            "uid": {
+              "type": "string"
+            }
+          },
+          "type": "object"
+        },
+        "unicode": {
+          "type": "string"
+        }
+      },
+      "type": "object"
+    },
+    "name": {
+      "type": "string"
+    },
+    "user": {
+      "properties": {
+        "avatarUrl": {
+          "type": "string"
+        },
+        "displayName": {
+          "type": "string"
+        },
+        "domainId": {
+          "type": "string"
+        },
+        "email": {
+          "type": "string"
+        },
+        "isAnonymous": {
+          "type": "boolean"
+        },
+        "name": {
+          "type": "string"
+        },
+        "type": {
+          "enum": [
+            "TYPE_UNSPECIFIED",
+            "HUMAN",
+            "BOT"
+          ],
+          "type": "string"
+        }
+      },
+      "type": "object"
+    }
+  },
+  "type": "object"
+}

Changed3 schema fields changedOct 26, 2026

changedInput schema / properties / parent / description

Previous value: -"Required. The message where the reaction is created. Format: `spaces/{space}/messages/{message}`"New value: +"[URL path segment] Required. The message where the reaction is created. Format: `spaces/{space}/messages/{message}`"

addedInput schema / properties / parent / pattern
```
Added value: +"^spaces/[^/]+/messages/[^/]+$"
```

changedOutput schema / (root)

Previous value: -nullNew value: +{
+  "properties": {
+    "emoji": {
+      "properties": {
+        "customEmoji": {
+          "properties": {
+            "emojiName": {
+              "type": "string"
+            },
+            "name": {
+              "type": "string"
+            },
+            "payload": {
+              "properties": {
+                "fileContent": {
+                  "type": "string"
+                },
+                "filename": {
+                  "type": "string"
+                }
+              },
+              "type": "object"
+            },
+            "temporaryImageUri": {
+              "type": "string"
+            },
+            "uid": {
+              "type": "string"
+            }
+          },
+          "type": "object"
+        },
+        "unicode": {
+          "type": "string"
+        }
+      },
+      "type": "object"
+    },
+    "name": {
+      "type": "string"
+    },
+    "user": {
+      "properties": {
+        "avatarUrl": {
+          "type": "string"
+        },
+        "displayName": {
+          "type": "string"
+        },
+        "domainId": {
+          "type": "string"
+        },
+        "email": {
+          "type": "string"
+        },
+        "isAnonymous": {
+          "type": "boolean"
+        },
+        "name": {
+          "type": "string"
+        },
+        "type": {
+          "enum": [
+            "TYPE_UNSPECIFIED",
+            "HUMAN",
+            "BOT"
+          ],
+          "type": "string"
+        }
+      },
+      "type": "object"
+    }
+  },
+  "type": "object"
+}

First observedOct 26, 2026

TDQS

A4/5.0

Behavior4/5

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

With no annotations supplied, the description carries the burden and does substantial work: it discloses the HTTP POST method, readonly-profile refusal, required user authentication with enumerated authorization scopes, and that the API response resource is returned as JSON. The scope list is truncated ('https://www.goog'), which blunts an otherwise strong disclosure.

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

Conciseness3/5

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

Purpose is front-loaded, which is good, but the definition is cluttered by a broken/truncated scope URL and a stack of concatenated metadata (method note, return note, sibling note). The truncation is dead weight that hurts an otherwise serviceable structure.

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?

Covers auth needs, safety/host-profile behavior, body shape and siblings, and an output schema exists so return-value detail isn't required. The cut-off scope list leaves one gap, but an agent has enough to invoke it correctly.

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 schema already documents parent format, query, params, dry_run and body_file. The description adds only that the body is a JSON Reaction object accepting emoji, name, user and that it can be passed via params or body_file — marginal reinforcement rather than new meaning.

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?

States a specific verb and resource: 'Creates a reaction and adds it to a message.' It also names the sibling operations over the same resource (delete, list), so the agent can separate this from chat.spaces.messages.reactions.delete/list and messagePins tools.

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

Usage Guidelines4/5

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

Gives clear context (creating a reaction on a message) and flags that the operation is refused under --readonly safety profiles, which is a real usage constraint. It does not spell out a when-not-to-use condition or a distinct alternative path, so it falls just short of a 5.

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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