Record a slowdown, then compare before and after

Steps

1. 01Step 1 of 10

   Step 1. Start recording

   Press ⇧⌘R, or click Record in the title bar. Black bars close in on the stage with a running clock, and the bottom of the window shows REC. Recording works from any page.

   OverviewUnderstand what your Mac is doing, and what is using its resources.

   SummaryDashboardSearch or jump to…⌘KPauseStop

   Rec00:01:2442 samples · system 2s

   Live10:42:18

   No warning in assessed readings.

   Lumen Edit uses 212.4% CPU across 6 processes, where 100% is one core.

   Pressure NormalThermal Nominal

   486 processes · 3,912 threadsUp 4d 3h · swap 0 bytes

   Export Visual Snapshot…

   Apple M4 Prosystem on chip · 14 CPU cores · 48 GB unified memory

   CPUwhole Mac · every 2s

   24%

   User17.6%System6.4%Idle76.0%

   GPUevery 5s

   18%

   Renderer16%

   Tiler9%

   Neural Engine

   0.42W

   power, not utilizationpeak 2.31 W · 120 s

   Unified memoryshared by CPU, GPU and Neural Engine

   21.4GBestimated used of 48 GB · 44.6%

   App14.2 GBWired4.1 GBCompressed3.1 GB

   Cache12.8 GBFree13.8 GB

   Component power

   14.2Wpeak 31.6 W

   CPU 9.6 · GPU 4.2 · ANE 0.42 W

   Diskevery 2s

   Read2.1 MB/s

   Write1.1 MB/s

   Networkevery 2s

   Received1.6 MB/s

   Sent210 KB/s

   Recording to SessionsStop with ⇧⌘R

   Live timelineLatest 120 seconds on one clock · hover to rewind the stage, click to pin · gaps stay visible

   CPUevery 2s

   24%User 17.6% · System 6.4%

   100%0

   GPUevery 5s

   18%Renderer 16% · Tiler 9%

   100%0

   Neural Engineevery 5s

   0.42 Wpower, not utilization

   2.5 W0

   Memoryevery 2s

   21.4 GBPressure Normal

   48 GB0

   Diskevery 2s

   3.2 MB/sRead 2.1 · Write 1.1 MB/s

   ↑ 20 MB/s↓ 20 MB/s

   Networkevery 2s

   1.8 MB/sReceived 1.6 MB/s · Sent 210 KB/s

   ↑ 5 MB/s↓ 5 MB/s

   Apps using CPUApp helpers are included · 100% means one busy core

   L

   Lumen Edit6 processes

   212.4%

   K

   Kite Browser23 processes

   38.6%

   F

   Forge IDE14 processes

   24.9%

   H

   Harbor9 processes

   18.2%

   R

   Roundtable5 processes

   9.8%

   Sample 10:42:18Explore all processes

   What the numbers meanObservations from the displayed sample

   Info

   Lumen Edit leads measured CPU usageIt uses 212.4% CPU across 6 processes, where 100% is one core.

   Info

   Memory pressure is normalmacOS is meeting demand without heavy compression or swap.

2. 02Step 2 of 10

   Step 2. Do the slow thing, then stop

   Repeat what was slow. When it is over, press ⇧⌘R again. On the Sessions page (⌘8) you can watch the recording grow while it runs: the clock, the number of samples and how much room is left before a limit.

   SessionsRecord, replay, export, and compare monitoring sessions.

   Search or jump to…⌘KPauseStop

   Rec00:01:2442 samples · system 2s

   Recording10:42:18

   Recording since 10:40:54.

   Recording: Session 13 Oct 2026 at 10:40

   Recordings retain sampled system and process measurements, including exited processes.

   Sessions remain in ~/Library/Application Support/app.activity…/Profile/Sessions.

   00:01:24

   42 samples · 1.8 MB compressed · system 2sapproximately 23h 58m remaining at the current write rate

   Stop

   Saved sessions4most recent 13 Oct 2026 at 10:40

   Recording limitsChange in Settings

   24 hoursduration2 GiBcompressed86,400system samples100 millionprocess records

   Settings changes apply to the next recording.

   Recording to SessionsStop with ⇧⌘R

   Saved sessionsRefresh

   A strip draws average CPU by minute for the sessions you open.

   Search recording names and markers

   Session 13 Oct 2026 at 10:4013 Oct 2026 at 10:40 · 42 samples

   Name & markers…

   Recording

   After update13 Oct 2026 at 10:28 · 159 samples

   Replay

   00:05:18Complete

   2 markers · Started export · Export finished

   Before update12 Oct 2026 at 16:05 · 162 samples

   Replay

   00:05:24Complete

   2 markers · Started export · Export finished

   Session 11 Oct 2026 at 09:1411 Oct 2026 at 09:14 · 428 samples

   Replay

   00:14:16Complete

   Newest first · Session trash: /Users/sam/Library/Application Support/app.activity.desktop/Profile/Sessions/TrashExports…

   New recordings use compressed, disk-backed pages. Limits can stop a recording earlier; the reason is preserved. Saved sessions are never automatically deleted.

   Replay

   No session is being replayedChoose Replay on a saved session to review its complete recording, page through its detail samples, and compare it with the comparison baseline.

   No comparison baselineChoose Use as Comparison Baseline from a saved session’s menu, then replay another session to compare measured averages and workload changes.

   Portable and recoverableRecordings may contain executable paths, process owners, interface names, and sampled diagnostics. Exports include the full saved history. Moving a session to the session trash keeps its files in /Users/sam/Library/Application Support/app.activity.desktop/Profile/Sessions/Trash; nothing is permanently erased by l/Activity.

3. 03Step 3 of 10

   Step 3. Give it a name you will recognise

   The new recording appears at the top of Saved sessions. Open its … menu and choose Name & markers….

   SessionsRecord, replay, export, and compare monitoring sessions.

   Search or jump to…⌘KPauseRecord

   Ready10:42:18

   Record what this Mac does, then replay it.

   Recordings retain sampled system and process measurements, including exited processes.

   Sessions remain in ~/Library/Application Support/app.activity…/Profile/Sessions.

   Record

   Capture a baseline, make a change, then record a second session.

   Saved sessions3most recent 13 Oct 2026 at 10:28

   New recording limitsChange in Settings

   24 hoursduration2 GiBcompressed86,400system samples100 millionprocess records

   Saved sessionsRefresh

   A strip draws average CPU by minute for the sessions you open.

   Search recording names and markers

   After update13 Oct 2026 at 10:28 · 159 samples

   Replay

   Name & markers…

   Use as Comparison Baseline

   Export Full JSON…

   Export Full CSV…

   Move to Session Trash

   00:05:18Complete

   2 markers · Started export · Export finished

   Before update12 Oct 2026 at 16:05 · 162 samples

   Replay

   00:05:24Complete

   2 markers · Started export · Export finished

   Session 11 Oct 2026 at 09:1411 Oct 2026 at 09:14 · 428 samples

   Replay

   00:14:16Complete

   Newest first · Session trash: /Users/sam/Library/Application Support/app.activity.desktop/Profile/Sessions/TrashExports…

   New recordings use compressed, disk-backed pages. Limits can stop a recording earlier; the reason is preserved. Saved sessions are never automatically deleted.

   Replay

   No session is being replayedChoose Replay on a saved session to review its complete recording, page through its detail samples, and compare it with the comparison baseline.

   No comparison baselineChoose Use as Comparison Baseline from a saved session’s menu, then replay another session to compare measured averages and workload changes.

   Portable and recoverableRecordings may contain executable paths, process owners, interface names, and sampled diagnostics. Exports include the full saved history. Moving a session to the session trash keeps its files in /Users/sam/Library/Application Support/app.activity.desktop/Profile/Sessions/Trash; nothing is permanently erased by l/Activity.

4. 04Step 4 of 10

   Step 4. Mark the moments that matter

   Type a name and click Save Name. Then add markers: a label such as "Started export" and the number of seconds from the start. Markers show on the recording, can be searched, and can be used as starting points when you compare.

   SessionsRecord, replay, export, and compare monitoring sessions.

   Search or jump to…⌘KPauseRecord

   Replaying a saved session · 13 Oct 2026 at 10:31:06Return to Live

   Ready10:42:18

   Record what this Mac does, then replay it.

   Recordings retain sampled system and process measurements, including exited processes.

   Sessions remain in ~/Library/Application Support/app.activity…/Profile/Sessions.

   Record

   Capture a baseline, make a change, then record a second session.

   Saved sessions3most recent 13 Oct 2026 at 10:28

   New recording limitsChange in Settings

   24 hoursduration2 GiBcompressed86,400system samples100 millionprocess records

   Saved sessionsRefresh

   A strip draws average CPU by minute for the sessions you open.

   Search recording names and markers

   After update13 Oct 2026 at 10:28 · 159 samples

   Replay

   00:05:18Complete

   2 markers · Started export · Export finished

   Replay

   Before update12 Oct 2026 at 16:05 · 162 samples

   Replay

   00:05:24Complete

   2 markers · Started export · Export finished

   Session 11 Oct 2026 at 09:1411 Oct 2026 at 09:14 · 428 samples

   Replay

   00:14:16Complete

   Newest first · Session trash: /Users/sam/Library/Application Support/app.activity.desktop/Profile/Sessions/TrashExports…

   New recordings use compressed, disk-backed pages. Limits can stop a recording earlier; the reason is preserved. Saved sessions are never automatically deleted.

   Replay: After update159 recovered samples

   Complete

   159 detail samples on this page · 159 in recordingEarlierLater

   Complete recording overview

   Explore timelineReturn to Live

   No comparison baselineChoose Use as Comparison Baseline from a saved session’s menu, then replay another session to compare measured averages and workload changes.

   Portable and recoverableRecordings may contain executable paths, process owners, interface names, and sampled diagnostics. Exports include the full saved history. Moving a session to the session trash keeps its files in /Users/sam/Library/Application Support/app.activity.desktop/Profile/Sessions/Trash; nothing is permanently erased by l/Activity.

   Recording name & markers

   After updateSave Name

   Markers describe what you did. They do not change samples or establish a cause.

   Marker, e.g. Started export186seconds

   Use inspected timeAdd Marker

   0–318 seconds · up to 64 markers · labels up to 160 characters

   10:28:42Started exportInspectRemove

   10:33:18Export finishedInspectRemove

   Done

5. 05Step 5 of 10

   Step 5. Make your change and record again

   Update the app, change the setting, close the other apps, whatever you want to test. Then record the same task a second time and name it.

6. 06Step 6 of 10

   Step 6. Choose the baseline

   On the earlier recording, open … and choose Use as Comparison Baseline. A chip on it now reads Comparison baseline.

   SessionsRecord, replay, export, and compare monitoring sessions.

   Search or jump to…⌘KPauseRecord

   Ready10:42:18

   Record what this Mac does, then replay it.

   Recordings retain sampled system and process measurements, including exited processes.

   Sessions remain in ~/Library/Application Support/app.activity…/Profile/Sessions.

   Record

   Capture a baseline, make a change, then record a second session.

   Saved sessions3most recent 13 Oct 2026 at 10:28

   New recording limitsChange in Settings

   24 hoursduration2 GiBcompressed86,400system samples100 millionprocess records

   Saved sessionsRefresh

   A strip draws average CPU by minute for the sessions you open.

   Search recording names and markers

   After update13 Oct 2026 at 10:28 · 159 samples

   Replay

   00:05:18Complete

   2 markers · Started export · Export finished

   Before update12 Oct 2026 at 16:05 · 162 samples

   Replay

   00:05:24Complete

   2 markers · Started export · Export finished

   Session 11 Oct 2026 at 09:1411 Oct 2026 at 09:14 · 428 samples

   Replay

   00:14:16Complete

   Newest first · Session trash: /Users/sam/Library/Application Support/app.activity.desktop/Profile/Sessions/TrashExports…

   New recordings use compressed, disk-backed pages. Limits can stop a recording earlier; the reason is preserved. Saved sessions are never automatically deleted.

   Replay

   No session is being replayedChoose Replay on a saved session to review its complete recording, page through its detail samples, and compare it with the comparison baseline.

   No comparison baselineChoose Use as Comparison Baseline from a saved session’s menu, then replay another session to compare measured averages and workload changes.

   Portable and recoverableRecordings may contain executable paths, process owners, interface names, and sampled diagnostics. Exports include the full saved history. Moving a session to the session trash keeps its files in /Users/sam/Library/Application Support/app.activity.desktop/Profile/Sessions/Trash; nothing is permanently erased by l/Activity.

7. 07Step 7 of 10

   Step 7. Replay the other one

   Click Replay on the later recording. l/Activity opens it in History, where you can step through it like live history. Press ⌘8 to come back to Sessions.

   SessionsRecord, replay, export, and compare monitoring sessions.

   Search or jump to…⌘KPauseRecord

   Ready10:42:18

   Record what this Mac does, then replay it.

   Recordings retain sampled system and process measurements, including exited processes.

   Sessions remain in ~/Library/Application Support/app.activity…/Profile/Sessions.

   Record

   Capture a baseline, make a change, then record a second session.

   Saved sessions3most recent 13 Oct 2026 at 10:28

   New recording limitsChange in Settings

   24 hoursduration2 GiBcompressed86,400system samples100 millionprocess records

   Saved sessionsRefresh

   A strip draws average CPU by minute for the sessions you open.

   Search recording names and markers

   After update13 Oct 2026 at 10:28 · 159 samples

   Replay

   00:05:18Complete

   2 markers · Started export · Export finished

   Before update12 Oct 2026 at 16:05 · 162 samples

   Replay

   00:05:24Complete

   2 markers · Started export · Export finished

   Session 11 Oct 2026 at 09:1411 Oct 2026 at 09:14 · 428 samples

   Replay

   00:14:16Complete

   Newest first · Session trash: /Users/sam/Library/Application Support/app.activity.desktop/Profile/Sessions/TrashExports…

   New recordings use compressed, disk-backed pages. Limits can stop a recording earlier; the reason is preserved. Saved sessions are never automatically deleted.

   Replay

   No session is being replayedChoose Replay on a saved session to review its complete recording, page through its detail samples, and compare it with the comparison baseline.

   No comparison baselineChoose Use as Comparison Baseline from a saved session’s menu, then replay another session to compare measured averages and workload changes.

   Portable and recoverableRecordings may contain executable paths, process owners, interface names, and sampled diagnostics. Exports include the full saved history. Moving a session to the session trash keeps its files in /Users/sam/Library/Application Support/app.activity.desktop/Profile/Sessions/Trash; nothing is permanently erased by l/Activity.

8. 08Step 8 of 10

   Step 8. Read the whole-recording comparison

   With a baseline set and a replay open, the right side fills in. Complete recording comparison sets the two recordings side by side: average CPU, GPU, power, energy, network and disk.

   SessionsRecord, replay, export, and compare monitoring sessions.

   Search or jump to…⌘KPauseRecord

   Replaying a saved session · 13 Oct 2026 at 10:28:00Return to Live

   Saved sessionsRefresh

   A strip draws average CPU by minute for the sessions you open.

   Search recording names and markers

   After update13 Oct 2026 at 10:28 · 159 samples

   Replay

   00:05:18Complete

   2 markers · Started export · Export finished

   Replay

   Before update12 Oct 2026 at 16:05 · 162 samples

   Replay

   00:05:24Complete

   2 markers · Started export · Export finished

   Comparison baseline

   Session 11 Oct 2026 at 09:1411 Oct 2026 at 09:14 · 428 samples

   Replay

   00:14:16Complete

   Newest first · Session trash: /Users/sam/Library/Application Support/app.activity.desktop/Profile/Sessions/TrashExports…

   New recordings use compressed, disk-backed pages. Limits can stop a recording earlier; the reason is preserved. Saved sessions are never automatically deleted.

   Replay: After update159 recovered samples

   Complete

   159 detail samples on this page · 159 in recordingEarlierLater

   Complete recording overview

   Explore timelineReturn to Live

   Complete recording comparisonBaselineReplay

   System totals cover all saved pages. Missing source intervals are excluded. Totals depend on recording length; averages cover only measured time.

   MeasurementBaselineReplayCompare

   Average CPU61.2%38.4%

   Average device GPU44.7%41.9%

   Average CPU + GPU + ANE power38.62 W27.14 W

   Measured component energy3.48 Wh2.40 Wh

   Power coverage324 s318 s

   Physical network received18.4 MB16.9 MB

   Physical network sent2.1 MB1.9 MB

   Disk read4.82 GB4.79 GB

   Disk written9.64 GB9.61 GB

   Component energy excludes the rest of the Mac and wall-power losses. It is not per-app energy. Repeated cached source readings are counted once.

   Match comparison intervalsClear comparison baseline

   Choose the same duration in each recording. Paging through replay leaves this selection unchanged.

   Baseline: Before update

   Start42seconds from startUse Marker

   Replay: After update

   Start42seconds from startUse Marker

   Duration60seconds · maximum 300

   Baseline 12 Oct 2026 at 16:05:42–16:06:42Replay 13 Oct 2026 at 10:28:42–10:29:42

9. 09Step 9 of 10

   Step 9. Compare like with like

   Two recordings rarely start at the same instant. In Match comparison intervals, set a Start for each, by hand or with Use Marker, and a Duration of up to 300 seconds. Changes within selected intervals then shows the difference for the Mac and for each app, in percentage points.

   SessionsRecord, replay, export, and compare monitoring sessions.

   Search or jump to…⌘KPauseRecord

   Replaying a saved session · 13 Oct 2026 at 10:28:00Return to Live

   Match comparison intervalsClear comparison baseline

   Choose the same duration in each recording. Paging through replay leaves this selection unchanged.

   Baseline: Before update

   Start42seconds from startUse Marker

   Replay: After update

   Start42seconds from startUse Marker

   Duration60seconds · maximum 300

   Baseline 12 Oct 2026 at 16:05:42–16:06:42Replay 13 Oct 2026 at 10:28:42–10:29:42

   Measured coverage

   Equal elapsed intervals can have different sample coverage. Gaps, first baselines and unavailable readings contribute no rates.

   Baseline: 31 samples · CPU measured 60.0 of 60.0 sObserved samples 16:05:42–16:06:42

   Replay: 31 samples · CPU measured 60.0 of 60.0 sObserved samples 10:28:42–10:29:42

   Each selected interval keeps up to 600 system samples and 120,000 process records. Indexed recordings also cap decoded system data at 32 MiB per input. A clipped input remains explicitly partial.

   Changes within selected intervals

   Both inputs use the equal-duration ranges selected above. Averages are weighted by measured time; missing intervals and unmatched workloads remain unavailable. Complete-recording system totals are shown separately.

   Mac CPU change−22.8pp

   Baseline duration60.0s

   Replay duration60.0s

   WorkloadAverage CPU changeAverage memory change

   Lumen Edit−284.6 pp−1.2 GB

   Kite Browser+6.4 pp+310 MB

   Northwind Sync · new——

   CPU change in percentage points of one core · memory is sampled footprint; shared pages can overlap

10. 10Step 10 of 10

    Step 10. Export if you need to share it

    The … menu of any finished recording has Export Full JSON… and Export Full CSV…. Progress is listed under Exports… at the foot of the list.