# Check GA4 event parameters actually populate

> Tier: recipe. Operating recipe: real tool sequence, core rules, known traps.

Event parameters read for coverage: what the schema promises versus what events carry.

**Intent.** Declared parameters versus filled ones, the metadata truth.

## When to use

- Before parameter-based reports.
- After tagging changes.

## When not to use

- No specific contraindication beyond the preconditions below.

## Sources

Required: Google Analytics 4

## Preconditions

- The account is ticked in the dashboard, confirmed via list_accounts.

## Inputs

- `window`: Analysis window. Default: last 30 days.

## Procedure

1. Read declared parameters and custom definitions. — tools: `ga4_get_event_parameters`, `ga4_get_custom_definitions`
2. Verify population rates on the ones analyses need. — tools: `ga4_run_report`

## Decision rules

- **When** A registered dimension's parameter rarely populates → **conclude** Reports on it sample the minority: quantify the fill rate in every finding that uses it.

## Evidence requirements

- Every figure carries its account, metric and window.
- Anything below a readable sample size is reported as unjudged, not as zero.

## Human approval boundary

- The readout changes nothing. Any change it motivates goes through Safe Writes: preview, human confirmation, then apply.

## Failure modes

- Unregistered parameters are invisible to reports even when they populate.

## Output

- **Readout**: The figures, with windows and accounts named.
- **Flags**: What deserves a deeper skill or a human decision.