diff --git a/runtime/doc/options.txt b/runtime/doc/options.txt
index 7ab2390823..c477423ed7 100644
--- a/runtime/doc/options.txt
+++ b/runtime/doc/options.txt
@@ -6588,24 +6588,20 @@ A jump table for the options with a short description can be found at |Q_op|.
 				*'swapfile'* *'swf'* *'noswapfile'* *'noswf'*
 'swapfile' 'swf'	boolean	(default on)
 			local to buffer
-	Use a swapfile for the buffer.  This option can be reset when a
-	swapfile is not wanted for a specific buffer.  For example, with
-	confidential information that even root must not be able to access.
-	Careful: All text will be in memory:
-		- Don't use this for big files.
-		- Recovery will be impossible!
-	A swapfile will only be present when 'updatecount' is non-zero and
-	'swapfile' is set.
-	When 'swapfile' is reset, the swap file for the current buffer is
-	immediately deleted.  When 'swapfile' is set, and 'updatecount' is
-	non-zero, a swap file is immediately created.
-	Also see |swap-file|.
-	If you want to open a new buffer without creating a swap file for it,
-	use the |:noswapfile| modifier.
-	See 'directory' for where the swap file is created.
+	Use a |swap-file| for the buffer (if 'updatecount' is non-zero). The
+	'directory' option decides where swapfiles are stored.
 
-	This option is used together with 'bufhidden' and 'buftype' to
-	specify special kinds of buffers.   See |special-buffers|.
+	To open a new buffer without creating a swapfile, use |:noswapfile|.
+	To disable for an existing buffer, reset its 'swapfile' option.
+	Careful:
+		- Recovery will be impossible!
+		- The entire file will be in memory.
+
+	When reset, the swapfile for the current buffer is immediately
+	deleted.  When re-enabled (and 'updatecount' is non-zero), a swapfile
+	is immediately created.
+
+	Used with 'bufhidden' and 'buftype' to specify |special-buffers|.
 
 						*'switchbuf'* *'swb'*
 'switchbuf' 'swb'	string	(default "uselast")
@@ -7135,17 +7131,15 @@ A jump table for the options with a short description can be found at |Q_op|.
 						*'updatecount'* *'uc'*
 'updatecount' 'uc'	number	(default 200)
 			global
-	After typing this many characters the swap file will be written to
-	disk.  When zero, no swap file will be created at all (see chapter on
-	recovery |crash-recovery|).  'updatecount' is set to zero by starting
-	Vim with the "-n" option, see |startup|.  When editing in readonly
-	mode this option will be initialized to 10000.
-	The swapfile can be disabled per buffer with 'swapfile'.
-	When 'updatecount' is set from zero to non-zero, swap files are
-	created for all buffers that have 'swapfile' set.  When 'updatecount'
-	is set to zero, existing swap files are not deleted.
-	This option has no meaning in buffers where 'buftype' is "nofile" or
-	"nowrite".
+	The |swap-file| will be written after typing this many characters.
+
+	- Ignored in buffers where 'buftype' is "nofile" or "nowrite".
+	- Initialized to 10000 when editing in readonly |-R| mode.
+	- To disable swapfiles per-buffer, unset the 'swapfile' option.
+	- To disable swapfiles globally, set this option to zero (or start
+	  with |-n|). See |crash-recovery|. Existing swapfiles are not deleted.
+	- When re-enabled (from zero to non-zero), swapfiles are created for
+	  all buffers that have 'swapfile' set.
 
 						*'updatetime'* *'ut'*
 'updatetime' 'ut'	number	(default 4000)
diff --git a/runtime/lua/vim/_core/proc.lua b/runtime/lua/vim/_core/proc.lua
new file mode 100644
index 0000000000..36bde5309a
--- /dev/null
+++ b/runtime/lua/vim/_core/proc.lua
@@ -0,0 +1,20 @@
+-- OS/process utils.
+
+local M = {}
+
+--- Counts (approximate) open file descriptors for this process. Works on Linux/macOS/BSD.
+---@return integer? # Number of open fds, or nil if `/dev/fd` failed (fds exhausted, or unavailable/Windows).
+function M.count_open_fds()
+  local n = 0
+  for _, _, err in vim.fs.dir('/dev/fd', { err = true }) do
+    -- If `/dev/fd` scan failed (e.g. EMFILE when fds exhausted), count would be misleading.
+    if err then
+      return nil
+    end
+    n = n + 1
+  end
+  -- Discount the scan's own descriptor.
+  return math.max(0, n - 1)
+end
+
+return M
diff --git a/runtime/lua/vim/_meta/options.gen.lua b/runtime/lua/vim/_meta/options.gen.lua
index a647755522..d8773efc3b 100644
--- a/runtime/lua/vim/_meta/options.gen.lua
+++ b/runtime/lua/vim/_meta/options.gen.lua
@@ -7023,24 +7023,20 @@ vim.o.sua = vim.o.suffixesadd
 vim.bo.suffixesadd = vim.o.suffixesadd
 vim.bo.sua = vim.bo.suffixesadd
 
---- Use a swapfile for the buffer.  This option can be reset when a
---- swapfile is not wanted for a specific buffer.  For example, with
---- confidential information that even root must not be able to access.
---- Careful: All text will be in memory:
---- 	- Don't use this for big files.
---- 	- Recovery will be impossible!
---- A swapfile will only be present when 'updatecount' is non-zero and
---- 'swapfile' is set.
---- When 'swapfile' is reset, the swap file for the current buffer is
---- immediately deleted.  When 'swapfile' is set, and 'updatecount' is
---- non-zero, a swap file is immediately created.
---- Also see `swap-file`.
---- If you want to open a new buffer without creating a swap file for it,
---- use the `:noswapfile` modifier.
---- See 'directory' for where the swap file is created.
+--- Use a `swap-file` for the buffer (if 'updatecount' is non-zero). The
+--- 'directory' option decides where swapfiles are stored.
 ---
---- This option is used together with 'bufhidden' and 'buftype' to
---- specify special kinds of buffers.   See `special-buffers`.
+--- To open a new buffer without creating a swapfile, use `:noswapfile`.
+--- To disable for an existing buffer, reset its 'swapfile' option.
+--- Careful:
+--- 	- Recovery will be impossible!
+--- 	- The entire file will be in memory.
+---
+--- When reset, the swapfile for the current buffer is immediately
+--- deleted.  When re-enabled (and 'updatecount' is non-zero), a swapfile
+--- is immediately created.
+---
+--- Used with 'bufhidden' and 'buftype' to specify `special-buffers`.
 ---
 --- @type boolean
 vim.o.swapfile = true
@@ -7702,17 +7698,15 @@ vim.o.ur = vim.o.undoreload
 vim.go.undoreload = vim.o.undoreload
 vim.go.ur = vim.go.undoreload
 
---- After typing this many characters the swap file will be written to
---- disk.  When zero, no swap file will be created at all (see chapter on
---- recovery `crash-recovery`).  'updatecount' is set to zero by starting
---- Vim with the "-n" option, see `startup`.  When editing in readonly
---- mode this option will be initialized to 10000.
---- The swapfile can be disabled per buffer with 'swapfile'.
---- When 'updatecount' is set from zero to non-zero, swap files are
---- created for all buffers that have 'swapfile' set.  When 'updatecount'
---- is set to zero, existing swap files are not deleted.
---- This option has no meaning in buffers where 'buftype' is "nofile" or
---- "nowrite".
+--- The `swap-file` will be written after typing this many characters.
+---
+--- - Ignored in buffers where 'buftype' is "nofile" or "nowrite".
+--- - Initialized to 10000 when editing in readonly `-R` mode.
+--- - To disable swapfiles per-buffer, unset the 'swapfile' option.
+--- - To disable swapfiles globally, set this option to zero (or start
+---   with `-n`). See `crash-recovery`. Existing swapfiles are not deleted.
+--- - When re-enabled (from zero to non-zero), swapfiles are created for
+---   all buffers that have 'swapfile' set.
 ---
 --- @type integer
 vim.o.updatecount = 200
diff --git a/runtime/lua/vim/health/health.lua b/runtime/lua/vim/health/health.lua
index 2b26baf3bd..09b3882d40 100644
--- a/runtime/lua/vim/health/health.lua
+++ b/runtime/lua/vim/health/health.lua
@@ -208,6 +208,61 @@ local function check_watchers()
   )
 end
 
+--- Reads a single integer from a file (e.g. a `/proc/sys` entry).
+---@param path string
+---@return integer?
+local function read_int(path)
+  local ok, lines = pcall(vim.fn.readfile, path, '', 1)
+  local v = ok and lines[1] and tonumber(lines[1])
+  return v or nil
+end
+
+-- Note: this is part of check_performance().
+local function check_limits()
+  -- 'ulimit -n' (RLIMIT_NOFILE): each Nvim buffer may hold an open swapfile. Sockets, channels, filewatchers also consume file descriptors.
+  if vim.fn.has('win32') == 0 then
+    local ok, out = system({ 'sh', '-c', 'ulimit -Sn' }) -- Must use a shell.
+    out = vim.trim(out or '')
+    local soft = tonumber(out)
+    local used = require('vim._core.proc').count_open_fds()
+    local used_str = used and (', currently open: %d'):format(used) or ''
+    local raise_advice = {
+      '\'swapfile\' buffers, sockets, channels, and file-watchers consume file descriptors. A low limit causes "(libuv) kqueue(): Too many open files" (EMFILE) errors.',
+      'Increase the limit: add `ulimit -n 8192` to your shell rc. On macOS see also `launchctl limit maxfiles`; on Linux see `/etc/security/limits.conf` and systemd `LimitNOFILE`.',
+    }
+    if out == 'unlimited' then
+      health.ok(('ulimit -n (max open files): unlimited%s'):format(used_str))
+    elseif not ok or soft == nil then
+      health.info(('ulimit -n (max open files): unknown (%s)%s'):format(out, used_str))
+    elseif soft < 1024 then
+      health.warn(('ulimit -n (max open files) is low: %d%s'):format(soft, used_str), raise_advice)
+    elseif used and used > soft * 0.8 then
+      health.warn(
+        ('Open files near the limit: %d of %d (ulimit -n)'):format(used, soft),
+        raise_advice
+      )
+    else
+      health.ok(('ulimit -n (max open files): %d%s'):format(soft, used_str))
+    end
+  end
+
+  -- Linux inotify limits filewatchers (LSP, vim._watch). Exhausting them reports ENOSPC ("no space on device").
+  if vim.uv.os_uname().sysname == 'Linux' then
+    local watches = read_int('/proc/sys/fs/inotify/max_user_watches')
+    local instances = read_int('/proc/sys/fs/inotify/max_user_instances')
+    if watches and watches < 8192 then
+      health.warn(('fs.inotify.max_user_watches is low: %d'):format(watches), {
+        'Filewatchers may fail with ENOSPC. To increase the limit: `sysctl fs.inotify.max_user_watches=524288` (persist in /etc/sysctl.conf).',
+      })
+    end
+    if instances and instances < 128 then
+      health.warn(('fs.inotify.max_user_instances is low: %d'):format(instances), {
+        'To increase the limit: `sysctl fs.inotify.max_user_instances=512` (persist in /etc/sysctl.conf).',
+      })
+    end
+  end
+end
+
 local function check_performance()
   health.start('Performance')
 
@@ -240,6 +295,7 @@ local function check_performance()
   end
 
   check_watchers()
+  check_limits()
 end
 
 -- Load the remote plugin manifest file and check for unregistered plugins
diff --git a/runtime/lua/vim/pack/health.lua b/runtime/lua/vim/pack/health.lua
index 1590530fba..dff67ffffd 100644
--- a/runtime/lua/vim/pack/health.lua
+++ b/runtime/lua/vim/pack/health.lua
@@ -243,8 +243,13 @@ local function check_plug_dir()
 
   local is_good = true
   local plug_dir = get_plug_dir()
-  for plug_name, _ in vim.fs.dir(plug_dir) do
-    is_good = check_installed_plugin(plug_name) and is_good
+  for plug_name, _, err in vim.fs.dir(plug_dir, { err = true }) do
+    if err then
+      health.error(err)
+      is_good = false
+    else
+      is_good = check_installed_plugin(plug_name) and is_good
+    end
   end
 
   if is_good then
diff --git a/src/nvim/options.lua b/src/nvim/options.lua
index 20c000479c..ab6d99f1ce 100644
--- a/src/nvim/options.lua
+++ b/src/nvim/options.lua
@@ -9071,24 +9071,20 @@ local options = {
       cb = 'did_set_swapfile',
       defaults = true,
       desc = [=[
-        Use a swapfile for the buffer.  This option can be reset when a
-        swapfile is not wanted for a specific buffer.  For example, with
-        confidential information that even root must not be able to access.
-        Careful: All text will be in memory:
-        	- Don't use this for big files.
-        	- Recovery will be impossible!
-        A swapfile will only be present when 'updatecount' is non-zero and
-        'swapfile' is set.
-        When 'swapfile' is reset, the swap file for the current buffer is
-        immediately deleted.  When 'swapfile' is set, and 'updatecount' is
-        non-zero, a swap file is immediately created.
-        Also see |swap-file|.
-        If you want to open a new buffer without creating a swap file for it,
-        use the |:noswapfile| modifier.
-        See 'directory' for where the swap file is created.
+        Use a |swap-file| for the buffer (if 'updatecount' is non-zero). The
+        'directory' option decides where swapfiles are stored.
 
-        This option is used together with 'bufhidden' and 'buftype' to
-        specify special kinds of buffers.   See |special-buffers|.
+        To open a new buffer without creating a swapfile, use |:noswapfile|.
+        To disable for an existing buffer, reset its 'swapfile' option.
+        Careful:
+        	- Recovery will be impossible!
+        	- The entire file will be in memory.
+
+        When reset, the swapfile for the current buffer is immediately
+        deleted.  When re-enabled (and 'updatecount' is non-zero), a swapfile
+        is immediately created.
+
+        Used with 'bufhidden' and 'buftype' to specify |special-buffers|.
       ]=],
       full_name = 'swapfile',
       redraw = { 'statuslines' },
@@ -9942,17 +9938,15 @@ local options = {
       cb = 'did_set_updatecount',
       defaults = 200,
       desc = [=[
-        After typing this many characters the swap file will be written to
-        disk.  When zero, no swap file will be created at all (see chapter on
-        recovery |crash-recovery|).  'updatecount' is set to zero by starting
-        Vim with the "-n" option, see |startup|.  When editing in readonly
-        mode this option will be initialized to 10000.
-        The swapfile can be disabled per buffer with 'swapfile'.
-        When 'updatecount' is set from zero to non-zero, swap files are
-        created for all buffers that have 'swapfile' set.  When 'updatecount'
-        is set to zero, existing swap files are not deleted.
-        This option has no meaning in buffers where 'buftype' is "nofile" or
-        "nowrite".
+        The |swap-file| will be written after typing this many characters.
+
+        - Ignored in buffers where 'buftype' is "nofile" or "nowrite".
+        - Initialized to 10000 when editing in readonly |-R| mode.
+        - To disable swapfiles per-buffer, unset the 'swapfile' option.
+        - To disable swapfiles globally, set this option to zero (or start
+          with |-n|). See |crash-recovery|. Existing swapfiles are not deleted.
+        - When re-enabled (from zero to non-zero), swapfiles are created for
+          all buffers that have 'swapfile' set.
       ]=],
       full_name = 'updatecount',
       scope = { 'global' },
diff --git a/test/functional/core/main_spec.lua b/test/functional/core/main_spec.lua
index 7db780c425..90affba31b 100644
--- a/test/functional/core/main_spec.lua
+++ b/test/functional/core/main_spec.lua
@@ -228,6 +228,7 @@ describe('vim._core', function()
       'vim._core.help',
       'vim._core.log',
       'vim._core.options',
+      'vim._core.proc',
       'vim._core.server',
       'vim._core.shared',
       'vim._core.spell',