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AddEvent MCP by usefulapi
io.usefulapi/addevent in the official MCP registry.
Endpoint https://addevent.usefulapi.io/mcp. Source: github.com/m190/usefulapi-mcp.
The registry describes it as: Read AddEvent calendars, events, RSVPs and subscribers; create and update calendars and events.
We read its 18 tools on 2026-10-22. Nothing in them matched our tool-poisoning rules. It also sets server instructions, text a client puts in front of the model on connect; those were read too.
A clean read means these rules found nothing, not that the server is harmless. A server can change its tools at any time, which is why the index reads it again every week.
Tools it advertises
addevent_list_calendars addevent_get_calendar addevent_create_calendar addevent_update_calendar addevent_list_events addevent_get_event addevent_create_event addevent_update_event addevent_list_rsvp_attendees addevent_get_rsvp_attendee addevent_create_rsvp_attendee addevent_update_rsvp_attendee addevent_list_calendar_subscribers addevent_get_calendar_subscriber addevent_list_rsvp_forms addevent_list_event_templates addevent_list_calendar_templates addevent_list_timezones
Run this server? Show the check in your README
The badge reflects the latest weekly read: 
[](https://lazaretto.dev/mcp-registry/io-usefulapi-addevent)How this was checked
Lazaretto connects to the endpoint the way any MCP client does, asks the server to introduce itself and list its tools, and reads every name, description, parameter schema and server instruction for tool poisoning: hidden directive blocks, orders to read local secrets, parameters built to carry secrets or the conversation out, orders that redirect another server's tools, and invisible characters. It never calls a tool. What we found across the registry.
To run the same check every time Claude Code adds a server, install the free lazaretto-guard plugin. Browse every server in the index.