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Python
Hybrid

calendar_update_event

Update an existing calendar event; only non-empty fields change. For recurring events, choose scope (this/following/all) to set which occurrences update.

Instructions

Update an existing calendar event. For a recurring event, 'scope' controls which occurrences this touches: 'this' (default) affects only the given event_id; 'following' splits the series so this instance and every later one get the changes, leaving earlier ones untouched; 'all' updates the entire series. Only the fields you pass non-empty change; guests cannot be edited here. Returns {id, title, start_time, end_time, html_link}, plus conference_link when the event has a Google Meet. Use calendar_set_event_color or calendar_set_event_visibility to change only the color or visibility. Requires user approval.

Input Schema

NameRequiredDescriptionDefault
colorNoNew event color id (1-11) or name, e.g. "Tomato" -- see calendar_list_colors. Empty leaves the color unchanged.
roomsNoComma-separated room resource email addresses to book, from calendar_list_rooms (its resource_email field); they replace the rooms already booked. Empty leaves the rooms unchanged.
scopeNoFor a recurring event: 'this', 'following', or 'all'. Ignored (has no other meaning) for a non-recurring event.this
titleNoNew title. Empty leaves the title unchanged.
reasonYesOne sentence: why are you calling this tool right now?
end_timeNoNew end, same format as start_time. Empty leaves the end unchanged.
event_idYesId of the event, from calendar_list_events (its id field).
locationNoNew location, replacing the current one. Empty leaves it unchanged.
start_timeNoNew start as an RFC 3339 timestamp, e.g. '2026-10-15T09:00:00+02:00'; a time without an offset uses the event's own time zone (UTC if it has none). Empty leaves the start unchanged.
calendar_idYesId of the calendar, from calendar_list_calendars (its id field), or 'primary' for the user's main calendar.
descriptionNoNew description, replacing the current one. Empty leaves it unchanged.
send_updatesNoWho gets a notification email about this change: 'none', 'all', or 'externalOnly'. Omit to use Calendar's own default.
add_google_meetNoSet to true to add a Google Meet link (skipped if one already exists)

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed9 schema fields changed
    • addedInput schema / properties / calendar_id / description
      Added value: +"Id of the calendar, from calendar_list_calendars (its id field), or 'primary' for the user's main calendar."
    • changedInput schema / properties / color / description
      Previous value: -"Event color id (1-11) or name, e.g. \"Tomato\" -- see calendar_list_colors"New value: +"New event color id (1-11) or name, e.g. \"Tomato\" -- see calendar_list_colors. Empty leaves the color unchanged."
    • addedInput schema / properties / description / description
      Added value: +"New description, replacing the current one. Empty leaves it unchanged."
    • addedInput schema / properties / end_time / description
      Added value: +"New end, same format as start_time. Empty leaves the end unchanged."
    • addedInput schema / properties / event_id / description
      Added value: +"Id of the event, from calendar_list_events (its id field)."
    • addedInput schema / properties / location / description
      Added value: +"New location, replacing the current one. Empty leaves it unchanged."
    • changedInput schema / properties / rooms / description
      Previous value: -"Comma-separated room resource email addresses to book"New value: +"Comma-separated room resource email addresses to book, from calendar_list_rooms (its resource_email field); they replace the rooms already booked. Empty leaves the rooms unchanged."
    • addedInput schema / properties / start_time / description
      Added value: +"New start as an RFC 3339 timestamp, e.g. '2026-10-15T09:00:00+02:00'; a time without an offset uses the event's own time zone (UTC if it has none). Empty leaves the start unchanged."
    • addedInput schema / properties / title / description
      Added value: +"New title. Empty leaves the title unchanged."
  2. First observedv5.3.0

TDQS

A4.6/5.0
Behavior5/5

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

Adds substantial context beyond the annotations (readOnly=false, idempotent=false, destructive=false): partial-update semantics ('Only the fields you pass non-empty change'), a hard limitation ('guests cannot be edited here'), the exact return shape including conference_link, and an explicit 'Requires user approval' gate. These are exactly the behavioral facts an agent cannot derive from the schema or annotations.

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?

Front-loads purpose, then scope semantics, then mutation/return behavior – a logical order with no filler sentences. It is a dense single paragraph, though, and the three-way scope explanation would scan faster as a short list; a small structure cost.

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?

For a 13-parameter mutation tool with no output schema, the description covers the mutation model, the one ambiguous parameter's real-world effect, an unsupported operation, the return fields, and the approval requirement. Nothing an agent needs to invoke it correctly 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 the baseline is 3, but the description goes further by explaining what 'scope' actually does to a recurring series ('following' splits the series, leaving earlier occurrences untouched) – detail not present in the schema's terser enum explanation. Other parameters are left to the schema, which is adequate here.

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?

Opens with a specific verb+resource ('Update an existing calendar event') and explicitly distinguishes itself from the color/visibility-only siblings by naming calendar_set_event_color and calendar_set_event_visibility. An agent can route to or away from this tool without opening the 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 clear conditional guidance: use the dedicated color/visibility tools when only those fields change, and it explains when each 'scope' value applies. It does not state prerequisites (e.g., required permissions) or when to prefer create/delete over update, so it falls short of full when/when-not coverage.

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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