Your PC has been keeping a dated list of everything that has gone wrong on it, and you have almost certainly never seen it. It is not hidden, exactly.
It just is not anywhere you would think to look, and it turns "it has been playing up lately" into an actual date.
I pulled the count off this machine before writing, and there were 271 entries sitting in it.
Opening it, and the command that does it
One line, because the menus will not get you there.
Documented by Microsoft in its perfmon reference, the switch is listed plainly: "/rel | Starts the Reliability Monitor."
⭐ Press Windows key and R, type `perfmon /rel`, press Enter. That is the fastest route. No administrator prompt is needed.
⚡ Searching Start for "reliability" also finds it, under the name View reliability history.
⚠️ Give it ten or twenty seconds on first open. It builds the chart as it loads. An empty window is not a fault.
Ours: 271 events already recorded
The number that makes the point.
Ours, read straight off the machine used for this page. Windows had 271 reliability records stored, going back over the life of this installation. I read the count rather than opening the chart, because this machine was in use at the time.
⚡ Ask your own machine for the number. Nothing is written:
(Get-CimInstance Win32_ReliabilityRecords).Count⭐ Nobody set this up. Windows has been recording it on your machine since the day it was installed. Whether or not anyone ever looks.
What the line on the graph means
The bit that looks like a score and is not quite one.
Microsoft's definition, from its stability index page: "The System Stability Index is a number from 1 (least stable) to 10 (most stable) and is a weighted measurement derived from the number of specified failures seen over a rolling historical period."
And how it recovers: "Recent failures are weighted more heavily than past failures, allowing an improvement over time to be reflected in an ascending System Stability Index once a reliability issue has been resolved."
⭐ So a dip that climbs back means your problem stopped. That is more useful than the number itself.
⚠️ Microsoft also states that "Days when the system is powered off or in a sleep state are not used when calculating the System Stability Index." A laptop that lives closed has gaps rather than perfect days.
⚡ A dotted line means not enough data yet: "If there is not enough data to calculate a steady System Stability Index, the graphed line will be dotted."
Reading it properly takes one minute
How to actually use the thing.
⭐ Click the day where the line first drops. The panel underneath lists what happened on that date. By name.
⭐ The rows are grouped: application failures, Windows failures, miscellaneous failures, warnings, and information.
⚡ Information rows are the gold. Successful updates and driver installs appear there. That is how you match a crash to whatever went in the day before.
⚠️ Ours, and marked as ours: read the day before the drop, not the day of it. Whatever broke usually arrived first and failed later.
Why this beats Event Viewer for the question you have
Being fair to both tools.
⛔ Event Viewer holds far more and shows you all of it. That is exactly the problem when you only want to know what changed.
⭐ Reliability Monitor is filtered down to things that actually failed, laid out by date, with the updates alongside them.
⚡ Use it first. Then go to Event Viewer if you need the detail behind a specific row.
What it will not tell you
Honest, because this is a diary rather than a diagnosis.
⛔ It does not explain anything. It records that a program stopped responding, not why.
⚠️ A blue screen appears here as a Windows failure with a stop code. That number is the part that narrows the cause, and this screen only gives you the date it started.
⚠️ Hardware faults show up sideways or not at all. Device Manager carries the codes that name those.
⭐ And a machine that is merely slow may have a perfect score. Slowness is rarely a failure and it is measured differently.
The documentation is older than the feature deserves
Saying so, because it explains why nobody mentions this tool.
⚠️ We could not find a current consumer page for Reliability Monitor. The fullest description Microsoft publishes is archived documentation labelled for Windows Server 2008 and Windows Vista.
⭐ The tool itself is present and working on your Windows 11 machine. The archived pages still describe it accurately.
⚡ That gap is most of the reason this is unknown. A feature with no current page rarely turns up in an answer.
Status: read against Microsoft's perfmon reference and its archived System Stability Index documentation, 25 August 2026, on Windows 11. The perfmon reference gives the /rel switch, and the archived pages give the definition and range of the stability index, the weighting of recent failures, the treatment of powered-off days and the meaning of a dotted line. The count of 271 stored records was read on this PC.
How do I open Reliability Monitor in Windows 11?
Press Windows key and R, type perfmon /rel and press Enter. Microsoft documents that switch. Searching Start for reliability also finds it, listed as View reliability history.
What does the reliability score out of 10 mean?
It is the System Stability Index. Microsoft defines it as a weighted measurement from 1 to 10 derived from the failures your PC has recorded over a rolling period. Recent failures count for more, so the line climbs again once a problem stops.
Why does my graph have gaps or a dotted line?
Days when your PC was off or asleep are not counted. A machine that is rarely on has gaps. A dotted line means Windows does not yet have enough data to draw a steady index.
Is Reliability Monitor better than Event Viewer?
For the question "what changed just before this started", yes. It is filtered to actual failures and lays them out by date next to your updates. Event Viewer has far more detail. Go there once you know which day to look at.
The Short Version
- Windows key and R, then perfmon /rel, opens it. Microsoft documents that switch.
- This PC had 271 reliability records stored without anyone ever enabling it.
- The line is the System Stability Index, from 1 least stable to 10 most stable.
- Recent failures are weighted more heavily, so the line recovers once a fault stops.
- Days the PC was off or asleep are not counted, which is why graphs have gaps.
- Click the day the line first drops, then read the day before it.
- Information rows list successful updates and driver installs, which is the match you want.
- Microsoft's fullest documentation for it is archived under Windows Vista.
Where to Next
Press Windows key and R and run perfmon /rel right now. Ten seconds, and you will see a timeline of your own machine you have never looked at.
Find the day the line first dropped and read the rows underneath it. That date is usually the answer to what changed.
Then check the information rows for the day before. An update or a driver install sitting there is usually the culprit.
Anyone whose chart pinned a problem to a specific update, tell me which one in the comments. Those dates are worth comparing.
Isaac Smith is the founder and editor of PC Glance, a website that covers computers, laptops, and technology. He is a tech enthusiast and a computer geek who loves to share his insights and help his readers make smart choices when buying tech gadgets or laptops. He is always curious and updated about the latest tech trends.