# Diagnose a Google Ads CPA spike fast

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

The Google CPA-spike sequence: conversions first, then mix shifts, then auction, then bid changes.

**Intent.** Why Google CPA jumped: measurement, mix, competition or bids.

## When to use

- CPA jumped beyond noise on meaningful spend.

## When not to use

- Windows inside conversion lag: wait it out or say so.

## Sources

Required: Google Ads

## Preconditions

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

## Inputs

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

## Procedure

1. Split the spike: spend up, conversions down, or both. — tools: `google_ads_get_insights`
2. Check conversion actions for measurement moves. — tools: `google_ads_get_conversion_actions`
3. Check mix: did spend shift toward expensive campaigns or terms. — tools: `google_ads_get_search_terms`
4. Check bid strategy and target changes. — tools: `google_ads_get_change_events`, `google_ads_get_bidding_strategies`

## Decision rules

- **When** Conversions fell while clicks held → **conclude** Measurement or site first: route to tracking-audit before touching bids.
- **When** A target change predates the spike → **conclude** The strategy obeys its new number: the spike is the setting, working.

## 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

- Attribution lag makes the last 72h spike artificially: trim before judging.

## Output

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

## Related

- Skill: [tracking-audit](https://www.getmcpads.com/skills/tracking-audit.md)
- Skill: [campaign-anomaly-investigation](https://www.getmcpads.com/skills/campaign-anomaly-investigation.md)