m365-mcp

Update Event

calendar_update_event

Idempotent

Modify an Outlook calendar event's time, title, location, description, reminder, or attendees. Set confirm=true to send attendee updates when required.

Instructions

Change an event's time, title, location, description, reminder or attendees. If the event has attendees, or you add some, Outlook emails them an update, so confirm=true is then required. Returns the updated event.

Input Schema

TableJSON Schema

Name	Required	Description
`changes`	Yes	Fields to change (at least one).
`confirm`	No	Must be true to send updates to the attendees; set only after the user approves.
`event_id`	Yes	Event to change.
`account_id`	No	Account ID or email address. Omit when only one account is signed in.

Output Schema

TableJSON Schema

Name	Required	Description
`event`	Yes
`summary`	Yes	One-line human summary. The tool's text content is this result serialized as JSON (summary included), so a client that ignores structuredContent still sees every field.
`changed_fields`	Yes
`attendees_notified`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

Changed18 schema fields changedv1.0.0Sep 29, 2026

addedInput schema / $schema

Added value: +"https://json-schema.org/draft/2020-12/schema"

addedInput schema / additionalProperties
```
Added value: +false
```

addedInput schema / properties / account_id / description

Added value: +"Account ID or email address. Omit when only one account is signed in."

addedInput schema / properties / account_id / maxLength
```
Added value: +320
```
addedInput schema / properties / account_id / minLength
```
Added value: +1
```

addedInput schema / properties / changes

Added value: +{
+  "additionalProperties": false,
+  "description": "Fields to change (at least one).",
+  "minProperties": 1,
+  "properties": {
+    "attendees_add": {
+      "description": "Attendees to add.",
+      "items": {
+        "additionalProperties": false,
+        "description": "Meeting attendee.",
+        "properties": {
+          "address": {
+            "description": "Email address, e.g. jane@example.com.",
+            "format": "email",
+            "maxLength": 320,
+            "minLength": 3,
+            "type": "string"
+          },
+          "name": {
+            "description": "Display name.",
+            "maxLength": 255,
+            "type": "string"
+          },
+          "type": {
+            "default": "required",
+            "description": "Attendance type.",
+            "enum": [
+              "required",
+              "optional"
+            ],
+            "type": "string"
+          }
+        },
+        "required": [
+          "address"
+        ],
+        "type": "object"
+      },
+      "maxItems": 500,
+      "minItems": 1,
+      "type": "array"
+    },
+    "attendees_remove": {
+      "description": "Attendee addresses to remove.",
+      "items": {
+        "description": "Email address, e.g. jane@example.com.",
+        "format": "email",
+        "maxLength": 320,
+        "minLength": 3,
+        "type": "string"
+      },
+      "maxItems": 500,
+      "minItems": 1,
+      "type": "array",
+      "uniqueItems": true
+    },
+    "attendees_set": {
+      "description": "Replace the attendee list.",
+      "items": {
+        "additionalProperties": false,
+        "description": "Meeting attendee.",
+        "properties": {
+          "address": {
+            "description": "Email address, e.g. jane@example.com.",
+            "format": "email",
+            "maxLength": 320,
+            "minLength": 3,
+            "type": "string"
+          },
+          "name": {
+            "description": "Display name.",
+            "maxLength": 255,
+            "type": "string"
+          },
+          "type": {
+            "default": "required",
+            "description": "Attendance type.",
+            "enum": [
+              "required",
+              "optional"
+            ],
+            "type": "string"
+          }
+        },
+        "required": [
+          "address"
+        ],
+        "type": "object"
+      },
+      "maxItems": 500,
+      "type": "array"
+    },
+    "body": {
+      "description": "Description.",
+      "maxLength": 100000,
+      "type": "string"
+    },
+    "body_format": {
+      "default": "text",
+      "description": "Format of the body text you supply.",
+      "enum": [
+        "text",
+        "html"
+      ],
+      "type": "string"
+    },
+    "end": {
+      "description": "RFC 3339 date-time with offset, e.g. 2026-10-01T09:00:00+09:30.",
+      "format": "date-time",
+      "type": "string"
+    },
+    "is_all_day": {
+      "description": "All-day event (start and end at midnight in time_zone).",
+      "type": "boolean"
+    },
+    "location": {
+      "description": "Location text.",
+      "maxLength": 255,
+      "type": "string"
+    },
+    "reminder_minutes": {
+      "description": "Reminder before start, in minutes.",
+      "maximum": 40320,
+      "minimum": 0,
+      "type": "integer"
+    },
+    "show_as": {
+      "description": "How the time shows in your calendar.",
+      "enum": [
+        "free",
+        "tentative",
+        "busy",
+        "oof",
+        "workingElsewhere"
+      ],
+      "type": "string"
+    },
+    "start": {
+      "description": "RFC 3339 date-time with offset, e.g. 2026-10-01T09:00:00+09:30.",
+      "format": "date-time",
+      "type": "string"
+    },
+    "subject": {
+      "description": "Title.",
+      "maxLength": 255,
+      "minLength": 1,
+      "type": "string"
+    },
+    "time_zone": {
+      "description": "IANA time-zone name, e.g. Australia/Adelaide. Defaults to the mailbox time zone.",
+      "maxLength": 64,
+      "minLength": 1,
+      "type": "string"
+    }
+  },
+  "type": "object"
+}

addedInput schema / properties / confirm

Added value: +{
+  "default": false,
+  "description": "Must be true to send updates to the attendees; set only after the user approves.",
+  "type": "boolean"
+}

addedInput schema / properties / event_id / description
```
Added value: +"Event to change."
```
addedInput schema / properties / event_id / maxLength
```
Added value: +1024
```
addedInput schema / properties / event_id / minLength
```
Added value: +1
```

removedInput schema / properties / updates

Removed value: -{
-  "additionalProperties": true,
-  "type": "object"
-}

changedInput schema / required

Previous value: -[
-  "event_id",
-  "updates",
-  "account_id"
-]New value: +[
+  "event_id",
+  "changes"
+]

addedOutput schema / $defs

Added value: +{
+  "attendee": {
+    "additionalProperties": false,
+    "description": "Event attendee and their response.",
+    "properties": {
+      "address": {
+        "type": "string"
+      },
+      "name": {
+        "anyOf": [
+          {
+            "type": "string"
+          },
+          {
+            "type": "null"
+          }
+        ]
+      },
+      "response": {
+        "enum": [
+          "none",
+          "organizer",
+          "tentativelyAccepted",
+          "accepted",
+          "declined",
+          "notResponded"
+        ]
+      },
+      "type": {
+        "enum": [
+          "required",
+          "optional",
+          "resource"
+        ]
+      }
+    },
+    "required": [
+      "name",
+      "address",
+      "type",
+      "response"
+    ],
+    "type": "object"
+  },
+  "event_detail": {
+    "additionalProperties": false,
+    "description": "Event from m365_get. recurrence is a read-only human summary.",
+    "properties": {
+      "attendee_count": {
+        "minimum": 0,
+        "type": "integer"
+      },
+      "attendees": {
+        "items": {
+          "$ref": "#/$defs/attendee"
+        },
+        "type": "array"
+      },
+      "body": {
+        "anyOf": [
+          {
+            "type": "string"
+          },
+          {
+            "type": "null"
+          }
+        ]
+      },
+      "body_truncated": {
+        "type": "boolean"
+      },
+      "calendar_id": {
+        "anyOf": [
+          {
+            "type": "string"
+          },
+          {
+            "type": "null"
+          }
+        ]
+      },
+      "end": {
+        "format": "date-time",
+        "type": "string"
+      },
+      "id": {
+        "type": "string"
+      },
+      "is_all_day": {
+        "type": "boolean"
+      },
+      "is_organizer": {
+        "type": "boolean"
+      },
+      "location": {
+        "anyOf": [
+          {
+            "type": "string"
+          },
+          {
+            "type": "null"
+          }
+        ]
+      },
+      "my_response": {
+        "enum": [
+          "none",
+          "organizer",
+          "tentativelyAccepted",
+          "accepted",
+          "declined",
+          "notResponded"
+        ]
+      },
+      "organizer": {
+        "anyOf": [
+          {
+            "$ref": "#/$defs/recipient"
+          },
+          {
+            "type": "null"
+          }
+        ]
+      },
+      "preview": {
+        "anyOf": [
+          {
+            "maxLength": 255,
+            "type": "string"
+          },
+          {
+            "type": "null"
+          }
+        ]
+      },
+      "recurrence": {
+        "anyOf": [
+          {
+            "type": "string"
+          },
+          {
+            "type": "null"
+          }
+        ]
+      },
+      "show_as": {
+        "enum": [
+          "free",
+          "tentative",
+          "busy",
+          "oof",
+          "workingElsewhere",
+          "unknown"
+        ]
+      },
+      "start": {
+        "format": "date-time",
+        "type": "string"
+      },
+      "subject": {
+        "anyOf": [
+          {
+            "type": "string"
+          },
+          {
+            "type": "null"
+          }
+        ]
+      },
+      "time_zone": {
+        "type": "string"
+      },
+      "web_link": {
+        "anyOf": [
+          {
+            "type": "string"
+          },
+          {
+            "type": "null"
+          }
+        ]
+      }
+    },
+    "required": [
+      "id",
+      "subject",
+      "start",
+      "end",
+      "time_zone",
+      "is_all_day",
+      "location",
+      "organizer",
+      "is_organizer",
+      "my_response",
+      "show_as",
+      "attendee_count",
+      "calendar_id",
+      "preview",
+      "body",
+      "body_truncated",
+      "attendees",
+      "web_link",
+      "recurrence"
+    ],
+    "type": "object"
+  },
+  "recipient": {
+    "additionalProperties": false,
+    "description": "A person's name and address.",
+    "properties": {
+      "address": {
+        "type": "string"
+      },
+      "name": {
+        "anyOf": [
+          {
+            "type": "string"
+          },
+          {
+            "type": "null"
+          }
+        ]
+      }
+    },
+    "required": [
+      "name",
+      "address"
+    ],
+    "type": "object"
+  }
+}

addedOutput schema / $schema

Added value: +"https://json-schema.org/draft/2020-12/schema"

changedOutput schema / additionalProperties
```
Previous value: -trueNew value: +false
```
addedOutput schema / description
```
Added value: +"The updated event."
```

addedOutput schema / properties

Added value: +{
+  "attendees_notified": {
+    "type": "boolean"
+  },
+  "changed_fields": {
+    "items": {
+      "type": "string"
+    },
+    "type": "array"
+  },
+  "event": {
+    "$ref": "#/$defs/event_detail"
+  },
+  "summary": {
+    "description": "One-line human summary. The tool's text content is this result serialized as JSON (summary included), so a client that ignores structuredContent still sees every field.",
+    "type": "string"
+  }
+}

addedOutput schema / required

Added value: +[
+  "event",
+  "attendees_notified",
+  "changed_fields",
+  "summary"
+]

First observedv0.2.3Jun 10, 2026

TDQS

A4.2/5.0

Behavior4/5

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

Annotations cover the safety profile (readOnly=false, idempotent=true, destructive=false, openWorld=true), and the description adds a side effect the annotations cannot express: attendee notification emails, gated by confirm=true. That is exactly the extra context the annotations omit. It still does not state permission requirements or atomicity if a partial change fails.

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?

Two sentences, zero filler, and the mutation surface is front-loaded before the confirm-gate caveat. Nothing here is repeated boilerplate.

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?

An output schema exists, so explaining return values is unnecessary, and the description correctly spends its words on the confirm/notification behavior an agent must know before calling. It is nearly complete, missing only failure-mode context (e.g. what happens if confirm is false while attendees exist).

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%, with every field (start/end RFC 3339 format, time_zone IANA name, attendees_add/set/remove, reminder_minutes bounds) documented inline. The description only restates the field families at a high level and adds no syntax or format meaning beyond the schema, so the baseline 3 applies.

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 (change) and resource (event) and enumerates the mutable field families: time, title, location, description, reminder, attendees. This clearly distinguishes it from the sibling calendar_create_event without needing to open either schema.

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 an explicit conditional rule: if the event has attendees (or you add some), Outlook emails them and confirm=true is required. That is genuine when-to-do-what guidance. It stops short of routing the agent away from alternatives (e.g. calendar_respond for RSVPs), but no misleading or missing context.

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