Exploring MCP tool quality

Any MCP server instrumented with PostHog's MCP analytics SDK emits a $mcp_tool_call event on the shared events table every time an agent invokes a tool. There is no dedicated ClickHouse table — every field lives as a $mcp_* property on events, and every tool-quality metric (error rate, latency percentiles, reach) is an aggregation over this one event. This is the data behind the MCP analytics dashboard and tool-quality screens.

For a single tool, prefer the typed tools — posthog:query-mcp-tool-stats (calls, errors, p50/p95, users, sessions, intents), posthog:query-mcp-tool-failures (top error messages by harness), and posthog:query-mcp-tool-daily-stats (day-by-day trend). Each takes a toolName + dateRange, runs the same query runner as the tool-detail UI, and is gated behind the mcp-analytics flag — no hand-written SQL needed.