> ## Documentation Index
> Fetch the complete documentation index at: https://docs.mutagent.io/llms.txt
> Use this file to discover all available pages before exploring further.
# Diagnose
> Stage ④ — root-cause the failures on evidence and rank the remedies. Failures come from Evaluate; fixes go to Optimize.
Stage ④ of the loop · owned by the **Diagnostics** skill, which ships as part of [Helix](/helix/what-is-helix).
**Diagnose** takes the failures that [Evaluate](/helix/lifecycle/evaluate) flagged and finds *why*
they happened — grounded in your real traces, not guesses — then ranks the fixes.
It runs a set of **analyzer agents in parallel** across a slice of your traces; each returns findings
tied to specific runs, which Helix merges, de-duplicates, and ranks by expected impact.
## Run it
Point Helix at what's failing:
```text theme={null}
Diagnose why the Refund Processing agent keeps failing the policy check on partial refunds.
```
Other ways people ask:
* *Run a root cause analysis on the Deep Research agent's low-scoring runs and rank the fixes worth trying.*
* *Find the traces where the Refund Processing agent mis-read the dispute amount and surface the common pattern.*
## What you get
* **Root causes**, each tied to evidence from your traces.
* **Ranked remedies** — the changes most likely to move the verdict, in priority order.
Diagnose proposes; it doesn't apply. Remedies hand off to [Optimize](/helix/lifecycle/optimize),
which applies them only after you approve.
## Use it on its own
You don't have to run the whole loop to use this stage. Once Helix is installed, point Diagnose at
your agent's traces and it returns evidence-grounded root causes and ranked remedies on its own —
no spec, build, or evaluate pass required first.
Apply an approved remedy and re-run the loop.