gcal

update_event

Update an existing event by eventId. Dates/times are interpreted in the provided timezone. Can update individual fields (summary, description, location) OR update times (must provide all: startDate, endDate, and optionally startTime, endTime). WARNING: Empty strings/arrays CLEAR fields. The attendees param REPLACES the entire guest list and resets everyone's RSVP to needsAction — to accept/decline/tentatively respond for yourself, use respond_to_event instead. Cannot move between calendars. Returns updated event {id, summary, start, end, updated, ...}.

Input Schema

TableJSON Schema

Name	Required	Description	Default
`endDate`	No	End date in YYYY-MM-DD format (e.g., "2024-01-16" for all-day or "2024-01-15" for timed). Required if updating time
`endTime`	No	End time in HH:MM:SS format (e.g., "15:00:00"). Omit for all-day events
`eventId`	Yes	Event ID to update
`summary`	No	Event title/summary
`location`	No	Event location
`timeZone`	Yes	Timezone for interpreting dates and times (e.g., "America/Los_Angeles", "UTC", "Europe/London")
`attendees`	No	Array of attendee email addresses (replaces existing attendees)
`startDate`	No	Start date in YYYY-MM-DD format (e.g., "2024-01-15"). Required if updating time
`startTime`	No	Start time in HH:MM:SS format (e.g., "14:00:00"). Omit for all-day events
`calendarId`	Yes	Calendar ID from list_calendars
`description`	No	Event description
`sendUpdates`	No	Whether to send update notifications (all: notify all attendees, externalOnly: only non-Google Calendar users, none: no notifications)	all

Output Schema

TableJSON Schema

Name	Required	Description	Default
`id`	Yes
`end`	Yes
`start`	Yes
`status`	No
`summary`	Yes
`updated`	No
`htmlLink`	No
`location`	No
`attendees`	No
`description`	No
`hangoutLink`	No
`conferenceData`	No

Schema Changelog

Changes observed during successful MCP inspections.

Changed2 schema fields changedApr 18, 2026

addedOutput schema / properties / conferenceData

Added value: +{
+  "additionalProperties": false,
+  "properties": {
+    "conferenceId": {
+      "type": "string"
+    },
+    "conferenceSolution": {
+      "additionalProperties": false,
+      "properties": {
+        "iconUri": {
+          "type": "string"
+        },
+        "name": {
+          "type": "string"
+        }
+      },
+      "type": "object"
+    },
+    "entryPoints": {
+      "items": {
+        "additionalProperties": false,
+        "properties": {
+          "entryPointType": {
+            "type": "string"
+          },
+          "label": {
+            "type": "string"
+          },
+          "uri": {
+            "type": "string"
+          }
+        },
+        "required": [
+          "entryPointType",
+          "uri"
+        ],
+        "type": "object"
+      },
+      "type": "array"
+    }
+  },
+  "type": "object"
+}

addedOutput schema / properties / hangoutLink
```
Added value: +{
+  "type": "string"
+}
```

Changed8 schema fields changedApr 7, 2026
- removedInput schema / additionalProperties
```
Removed value: -false
```
- addedOutput schema / properties / attendees / items / properties / responseStatus / anyOf
```
Added value: +[
+  {
+    "type": "string"
+  },
+  {
+    "type": "null"
+  }
+]
```
- removedOutput schema / properties / attendees / items / properties / responseStatus / type
```
Removed value: -[
-  "string",
-  "null"
-]
```
- removedOutput schema / properties / end / $ref
```
Removed value: -"#/properties/start"
```
- addedOutput schema / properties / end / additionalProperties
```
Added value: +false
```
- addedOutput schema / properties / end / properties
```
Added value: +{
+  "date": {
+    "type": "string"
+  },
+  "dayOfWeek": {
+    "type": "string"
+  },
+  "time": {
+    "type": "string"
+  },
+  "timezone": {
+    "type": "string"
+  }
+}
```
- addedOutput schema / properties / end / required
```
Added value: +[
+  "date",
+  "dayOfWeek"
+]
```
- addedOutput schema / properties / end / type
```
Added value: +"object"
```

Changed1 schema field changedFeb 9, 2026

changedOutput schema / (root)

Previous value: -nullNew value: +{
+  "$schema": "http://json-schema.org/draft-07/schema#",
+  "additionalProperties": false,
+  "properties": {
+    "attendees": {
+      "items": {
+        "additionalProperties": false,
+        "properties": {
+          "email": {
+            "type": "string"
+          },
+          "responseStatus": {
+            "type": [
+              "string",
+              "null"
+            ]
+          }
+        },
+        "required": [
+          "email"
+        ],
+        "type": "object"
+      },
+      "type": "array"
+    },
+    "description": {
+      "type": "string"
+    },
+    "end": {
+      "$ref": "#/properties/start"
+    },
+    "htmlLink": {
+      "type": "string"
+    },
+    "id": {
+      "type": "string"
+    },
+    "location": {
+      "type": "string"
+    },
+    "start": {
+      "additionalProperties": false,
+      "properties": {
+        "date": {
+          "type": "string"
+        },
+        "dayOfWeek": {
+          "type": "string"
+        },
+        "time": {
+          "type": "string"
+        },
+        "timezone": {
+          "type": "string"
+        }
+      },
+      "required": [
+        "date",
+        "dayOfWeek"
+      ],
+      "type": "object"
+    },
+    "status": {
+      "type": "string"
+    },
+    "summary": {
+      "type": "string"
+    },
+    "updated": {
+      "type": "string"
+    }
+  },
+  "required": [
+    "id",
+    "summary",
+    "start",
+    "end"
+  ],
+  "type": "object"
+}

First observedJan 31, 2026

TDQS

A4.9/5.0

Behavior5/5

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

Annotations only indicate readOnlyHint=false and destructiveHint=false, but the description discloses critical behaviors: dates/times interpreted in provided timezone, empty strings/arrays clear fields, attendees param replaces the entire guest list and resets RSVP, and cannot move between calendars. This goes well beyond annotations and is essential for safe use.

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

Conciseness5/5

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

The description is concise yet information-dense. It front-loads the core purpose, then delivers each behavioral nuance in a single sentence per concept: timezone handling, field vs time updates, clearing warning, attendees replacement, calendar constraint, and return format. No filler.

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

Completeness5/5

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

Given 12 parameters and multiple update modes, the description covers all critical decision points and side effects. It explains the time update constraint, clearing behavior, attendee replacement, cross-calendar restriction, and mentions the return object. With an output schema present, nothing essential is missing.

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

Parameters4/5

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

Schema coverage is 100%, so baseline is 3. However, the description adds semantic value by clarifying the all-or-nothing requirement for time updates, the clearing behavior with empty strings, and that attendees replaces the list and resets RSVP. These insights are not fully apparent from the schema alone.

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 clearly states the verb 'Update' with a specific resource 'existing event by eventId'. It also specifies the scope of what can be updated (fields or times) and differentiates from respond_to_event and the inability to move calendars, making it distinct from siblings.

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

Usage Guidelines5/5

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

Explicitly provides when to use this tool vs alternatives: 'to accept/decline/tentatively respond for yourself, use respond_to_event instead.' Also specifies the conditions for updating times (must provide all startDate/endDate) and warns about clearing fields with empty strings, giving clear context for correct invocation.

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

All gcal tools Inspect

Try in Browser

One endpoint for every MCP toolRayrun runs every MCP server behind one URL and holds the credentials. Each call is decided per client, tool, and argument, then recorded.ray.runAd

Glama MCP Gateway

Add one secure layer between your agents and this server.