--- title: "How Sentinely measures memory and fixes · MacMelon" description: "What Sentinely measures, what a receipt means, how fixes stay safe, and what it never does: memory footprint, pressure, swap-in rate, no invented percentages." url: "https://macmelon.com/how-sentinely-measures" --- # How Sentinely measures Sentinely tells you why your Mac feels slow, fixes it carefully, and shows you a measured before-and-after. This page explains what we measure, what the numbers mean, and what we will never do. ## Why a Mac feels slow On a modern Mac, the usual cause of "it feels slow" is not the processor. It is memory. When apps together want more memory than the Mac has, macOS works harder to make room. The kernel tracks this as a [memory pressure](https://macmelon.com/glossary/memory-pressure) level. macOS first [compresses](https://macmelon.com/glossary/compressed-memory) memory that has not been used recently. That costs some processor time each time the data is needed again. When compression is not enough, macOS writes memory to disk as [swap](https://macmelon.com/glossary/swap-memory). The pause you feel when you switch back to an app is often macOS reading its memory back in. ## What we measure **Memory footprint.** The memory a process is responsible for, including its compressed memory. It is the number macOS itself uses to account for a process. We do not use resident size (RSS), which misses compressed memory and double-counts shared pages. See [memory footprint](https://macmelon.com/glossary/memory-footprint). **Pressure level.** The kernel's own memory-pressure state. It says whether the Mac is actually struggling, not just using a lot of memory. Using memory is normal. **Swap-in rate.** How often memory is being read back from swap. This is closest to what you feel. A large swap file that is not being read is mostly harmless. **Swap used.** How much memory has been written out to disk. Context for the swap-in rate, and one input to the restart rule below. A diagnosis names specific apps or groups of processes and estimates how much memory they hold. If nothing is wrong, Sentinely says so. ## What a receipt means Every fix produces a [measured receipt](https://macmelon.com/glossary/measured-receipt) with two results. **Freed** is the memory footprint of the processes that are now gone. It is measured at least ten seconds after the fix, from a fresh reading, and confirmed again at sixty seconds. **Felt** is what changed for you: memory pressure and swap-in rate before versus after, over the same window. Before a fix, estimates for a group of processes, such as an Electron app, are shown as "up to", because processes in a group share some memory. The receipt reports what was measured afterwards, which may be less. We do not convert results into time saved or a percentage faster. We cannot measure that honestly, so we do not claim it. Lifetime totals add up only bytes that were measured. ## How the freeze warning works macOS shows the Force Quit window (“Your system has run out of application memory”) when it can no longer find room for memory: swap is nearly full and the disk cannot take much more. Sentinely cannot read the kernel's exact limit, so it watches the signals that come before it. Every reading records swap in use, the swap space macOS has set aside so far, free disk space, the [memory pressure](https://macmelon.com/glossary/memory-pressure) level and the swap-in rate. From the last ten minutes it works out how fast swap is growing and how much room is left, and turns that into an estimated time. On screen it always says “estimate”. **Warning** means swap is filling and a freeze is likely if nothing changes. **Critical** is shown only when macOS also reports elevated pressure, or when swap is within about 1 GB of full on a disk that cannot hold more. We calibrated it on a real Force Quit window, and we would rather warn a little late than cry wolf, because a warning people learn to ignore protects no one. A warning arrives at most once per level, again only if things get worse, and never more than every few minutes. With Pro, Autopilot may act at **critical** without first waiting for memory to stay tight, but only with fixes you have approved before. It never quits an app on its own. ## How fixes stay safe - **Your processes only.** Sentinely acts only on processes running as you. It never touches system processes or anything owned by another user. - **Identity re-check.** Just before acting, including when Autopilot acts, Sentinely re-checks that each process is still the one it diagnosed. If anything changed, it does nothing. - **Graceful first.** Apps are asked to quit normally, so they can save your work. Chat apps are not quit while your microphone or camera is in use. - **You approve.** Manual fixes run when you choose Fix. Autopilot, in Pro, only acts on rules you have approved, after memory pressure has stayed high rather than on a brief spike, with daily limits and cool-downs. It only stops helpers you have already stopped once by hand, never quits apps, tells you after every action, and can be paused at any time. - **Restart advice is rare.** Sentinely suggests a restart only when pressure stays elevated after the recoverable problems are dealt with, and swap is at least half your memory or less than 2 GB of swap space is free. Never because of uptime alone. ## What we never do - No button that empties memory for show. Empty memory is not a goal; macOS uses spare memory as cache on purpose. - No freezing or suspending anything behind your back. Hold pauses an AI agent or a build only when you choose it, closes nothing, and resumes it on its own after 20 minutes. - No root helper, no admin password, and no kernel extensions. - No restart advice based on how long your Mac has been on. - No speed scores or invented percentages. - Nothing leaves your Mac except the license check, the update check, and fetching the current price and offers. ## Privacy of command lines To tell a stale dev server from a running one, Sentinely looks at process command lines. Command lines can contain secrets such as API keys, tokens, and passwords in URLs. - Secrets are redacted on your Mac, at the lowest level, before the rest of the app sees them. - Command lines are never stored, never shown raw, never exported, and never sent anywhere. - Receipts and the recovery history are kept locally in your user folder, readable only by you. ## Limitations - **Multi-process apps are estimates.** Electron apps and similar spread memory across many processes that share pages. Before a fix, Sentinely can only say "up to". The receipt shows what was measured. - **Memory is not everything.** A Mac can also be slow because of a full disk, heat, or a single process stuck at full CPU. Sentinely's fixes and receipts are about memory. For disk space, see [Disk Housekeeper](https://macmelon.com/apps/disk-housekeeper). - **Results vary.** If an app reopens or a stopped helper is started again, the memory comes back. A receipt measures that moment. It is not a promise. ## Questions about a measurement If a number looks wrong to you, write to harishganapathi@sevenhillshq.com with what you saw. We read everything. - [Sentinely](https://macmelon.com/apps/sentinely) - [How to find what's slowing down your Mac](https://macmelon.com/guides/how-to-find-what-is-slowing-down-your-mac) - [Why Sentinely won't "free your RAM"](https://macmelon.com/blog/why-sentinely-wont-free-your-ram)