Modify an existing local Calendar.app event by UID to update its title, start/end time, location, notes, or calendar; get the UID from apple_calendar_list_events.
Modify an existing local Calendar.app event. Obtain the uid from apple_calendar_list_events.
| Name | Required | Description | Default |
|---|---|---|---|
| end | No | ||
| uid | Yes | ||
| notes | No | ||
| start | No | ||
| title | No | ||
| allDay | No | ||
| calendar | Yes | Calendar name. | |
| location | No |
Changes observed during successful MCP inspections.
v3.0.0Input schema / properties / end / patternPrevious value: -"^(?:(?:\\d\\d[2468][048]|\\d\\d[13579][26]|\\d\\d0[48]|[02468][048]00|[13579][26]00)-02-29|\\d{4}-(?:(?:0[13578]|1[02])-(?:0[1-9]|[12]\\d|3[01])|(?:0[469]|11)-(?:0[1-9]|[12]\\d|30)|(?:02)-(?:0[1-9]|1\\d|2[0-8])))T(?:(?:[01]\\d|2[0-3]):[0-5]\\d(?::[0-5]\\d(?:\\.\\d+)?)?(?:Z|([+-](?:[01]\\d|2[0-3]):[0-5]\\d)))$"New value: +"^(?:(?:\\d\\d[2468][048]|\\d\\d[13579][26]|\\d\\d0[48]|[02468][048]00|[13579][26]00)-02-29|\\d{4}-(?:(?:0[13578]|1[02])-(?:0[1-9]|[12]\\d|3[01])|(?:0[469]|11)-(?:0[1-9]|[12]\\d|30)|(?:02)-(?:0[1-9]|1\\d|2[0-8])))T(?:(?:[01]\\d|2[0-3]):[0-5]\\d:[0-5]\\d(?:\\.\\d+)?(?:Z|([+-](?:[01]\\d|2[0-3]):[0-5]\\d)))$"Input schema / properties / start / patternPrevious value: -"^(?:(?:\\d\\d[2468][048]|\\d\\d[13579][26]|\\d\\d0[48]|[02468][048]00|[13579][26]00)-02-29|\\d{4}-(?:(?:0[13578]|1[02])-(?:0[1-9]|[12]\\d|3[01])|(?:0[469]|11)-(?:0[1-9]|[12]\\d|30)|(?:02)-(?:0[1-9]|1\\d|2[0-8])))T(?:(?:[01]\\d|2[0-3]):[0-5]\\d(?::[0-5]\\d(?:\\.\\d+)?)?(?:Z|([+-](?:[01]\\d|2[0-3]):[0-5]\\d)))$"New value: +"^(?:(?:\\d\\d[2468][048]|\\d\\d[13579][26]|\\d\\d0[48]|[02468][048]00|[13579][26]00)-02-29|\\d{4}-(?:(?:0[13578]|1[02])-(?:0[1-9]|[12]\\d|3[01])|(?:0[469]|11)-(?:0[1-9]|[12]\\d|30)|(?:02)-(?:0[1-9]|1\\d|2[0-8])))T(?:(?:[01]\\d|2[0-3]):[0-5]\\d:[0-5]\\d(?:\\.\\d+)?(?:Z|([+-](?:[01]\\d|2[0-3]):[0-5]\\d)))$"v2.1.1Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint=false, destructiveHint=true, idempotentHint=true, so the safety profile is covered and the description's 'Modify' is consistent with it. The description adds the uid-sourcing workflow but says nothing about whether omitted fields are preserved, whether this is a partial or full replacement, or what the destructive aspect actually destroys.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
Two short sentences, front-loaded with the action and immediately followed by the one prerequisite the agent needs. No filler.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
For a destructive, 8-parameter mutation with no output schema, the description is far too thin: it does not explain partial-update semantics, field replacement behavior, or what the destructive hint applies to. An agent has almost no guidance beyond the tool name.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema description coverage is 13% (only 'calendar' is documented) across 8 parameters, so the description carries the compensation burden and does not meet it. It clarifies where uid comes from but adds no meaning for start/end, title, notes, location, or allDay, nor whether they are optional partial updates.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
States a specific verb (Modify) and resource (an existing local Calendar.app event), and 'existing' implicitly distinguishes it from apple_calendar_create_event and apple_calendar_delete_event. It does not, however, distinguish it from the other calendar mutators (set_recurrence, add_alarm, set_url).
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
Gives one concrete prerequisite – obtain the uid from apple_calendar_list_events – which is a real workflow pointer. It never says when to use this tool versus the narrower siblings that mutate a single aspect of an event (add_alarm, set_recurrence, set_url), so usage is implied rather than stated.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.