Query traces with MCP
Contents
The PostHog MCP server lets your AI coding agent query LLM traces directly from your code editor. Check costs, monitor errors, and analyze model performance – without switching to the PostHog app.
This works in any MCP client – Cursor, Codex, Claude Code, Windsurf, VS Code, and others.
How it works
With MCP, your coding agent can:
- Check costs before and after deploys – "What's my LLM spend today vs yesterday?" to catch cost regressions
- Monitor error rates – "Are there any LLM errors in the last hour?" to detect issues early
- Compare models – "Compare latency between GPT-4 and Claude for the chat feature" to evaluate model choices
- Investigate specific traces – "Show me the most expensive LLM call from today" to find optimization opportunities
AI Observability tools
The MCP server provides these tools for working with LLM traces:
| Tool | Description |
|---|---|
get-llm-total-costs-for-project | Get total LLM costs for the project, broken down by model. Useful for monitoring spend and detecting cost anomalies. |
query-run | Run a custom HogQL query against your LLM trace data. Supports filtering by model, feature, cost, latency, error status, and time range. |
A typical workflow starts with get-llm-total-costs-for-project to check overall spend and identify which models are most expensive, then uses query-run with a HogQL query to drill into specific traces by feature, time range, or cost threshold.
Querying prompts and completions? The large content fields –
$ai_input,$ai_output_choices,$ai_input_state,$ai_output_state, and$ai_tools– live only on theposthog.ai_eventstable, notevents. Queryposthog.ai_eventsand anchor ontrace_idto read them. Metadata like model, cost, token counts, and trace IDs stays onevents. Rows inposthog.ai_eventsare dropped after the retention period (30 days by default), but rows ineventshave the same retention policy as product analytics events.
Example prompts
Try these with your MCP-enabled agent:
What are my total LLM costs this week, broken down by model?Find the most expensive LLM calls from the last 24 hours.Are there any LLM errors today?Compare token usage between GPT-4 and Claude for the search feature.How has LLM latency changed over the past 7 days?Show me traces where a single call cost more than $0.50.
Install the MCP server
The recommended way to install is with the AI wizard:
The wizard supports Claude, Cursor, Windsurf, VS Code, and more. You can also configure it manually.
See the MCP server docs for full setup instructions.