> For clean Markdown of any page, append .md to the page URL.
> For a complete documentation index, see https://docs.cessy.ai/inspect-and-operate/llms.txt.
> For AI client integration (Claude Code, Cursor, etc.), connect to the MCP server at https://docs.cessy.ai/_mcp/server.

# Data And Activity

> Inspect Cessy runtime state, events, projections, commands, policies, webhooks, agents, and errors during builder verification.

Use Data Explorer and Activity together. Data Explorer shows current read state. Activity explains how the app got there.

## Data Explorer

Use Data Explorer to inspect published projection state:

* verify command results after smoke tests
* inspect list and detail projections used by custom pages
* check filters, sorting, and pagination behavior
* compare preview or test environments with production

If projection data looks wrong, inspect the event history and projection definition before changing frontend code.

## Activity

Use Activity to follow runtime behavior:

* command requests
* emitted events
* policy executions
* webhook handling
* subscription delivery
* adapter calls
* runtime agent actions
* errors and retries

Activity is the first place to look when a command succeeds but downstream behavior does not happen.

## Builder verification loop

After publish:

1. execute one representative command
2. confirm the expected event was emitted
3. confirm the projection changed
4. confirm policy, webhook, adapter, or subscription effects
5. check errors before handing off

## Agent-assisted debugging

A Design MCP agent can inspect the model and explain likely causes. A Runtime MCP agent can operate the published app. Keep those roles separate during debugging so the investigation does not accidentally mutate design state.

> Inspect Cessy runtime state, events, projections, commands, policies, webhooks, agents, and errors during builder verification.

## Docs

- [Observability](https://docs.cessy.ai/inspect-and-operate/observability.md): Observe Cessy command execution, events, projections, policies, adapters, webhooks, subscriptions, agents, pages, and errors.
- [Errors](https://docs.cessy.ai/inspect-and-operate/errors.md): Understand Cessy error statuses, response envelopes, command failures, policy failures, webhook failures, and troubleshooting order.