diff --git a/README.md b/README.md
index fa62174..f6d7df9 100644
--- a/README.md
+++ b/README.md
@@ -398,6 +398,8 @@ which is where this is usually installed by `snap`.
 Highlight groups that are user configurable to change the appearance of certain UI elements.
 
 - `FlutterToolsOutlineIndentGuides` - indent guides for the outline window
+- `FlutterToolsDimmed` - de-emphasised text: closing tags, outline return types and menu hints.
+  Links to Nvim 0.13's built-in `Dimmed` group where available, and to `Comment` otherwise.
 
 #### Widget guides
 
diff --git a/ftplugin/dart/init.lua b/ftplugin/dart/init.lua
index 3220e12..23ec60e 100644
--- a/ftplugin/dart/init.lua
+++ b/ftplugin/dart/init.lua
@@ -9,7 +9,7 @@ local path = require("flutter-tools.utils.path")
 
 vim.opt_local.comments = [[sO:*\ -,mO:*\ \ ,exO:*/,s1:/*,mb:*,ex:*/,:///,://]]
 vim.opt_local.commentstring = [[//%s]]
-vim.opt.includeexpr = "v:lua.require('flutter-tools.resolve_url').resolve_url(v:fname)"
+vim.opt_local.includeexpr = "v:lua.require('flutter-tools.resolve_url').resolve_url(v:fname)"
 
 local full_path = vim.fn.expand("%:p")
 -- Prevent writes to files in the pub cache and FVM folder.
diff --git a/lua/flutter-tools/config.lua b/lua/flutter-tools/config.lua
index bbc42ca..6d1b6de 100644
--- a/lua/flutter-tools/config.lua
+++ b/lua/flutter-tools/config.lua
@@ -115,7 +115,7 @@ local config = {
     register_configurations = nil,
   },
   closing_tags = {
-    highlight = "Comment",
+    highlight = ui.DIM_HL,
     prefix = "// ",
     priority = 10,
     enabled = true,
diff --git a/lua/flutter-tools/dev_tools.lua b/lua/flutter-tools/dev_tools.lua
index 584cc93..6fb26b6 100644
--- a/lua/flutter-tools/dev_tools.lua
+++ b/lua/flutter-tools/dev_tools.lua
@@ -45,19 +45,8 @@ end
 
 ---@param url string
 local function open_dev_tools(url)
-  local open_command, args = utils.open_command()
-  if not open_command then
-    return ui.notify(
-      "Sorry your Operating System is not supported, please raise an issue",
-      ui.ERROR
-    )
-  end
-  table.insert(args, url)
-  Job:new({
-    command = open_command,
-    args = args,
-    detached = true,
-  }):start()
+  local _, err = vim.ui.open(url)
+  if err then return ui.notify(err, ui.ERROR) end
 end
 
 local function start_browser()
diff --git a/lua/flutter-tools/lsp/color/init.lua b/lua/flutter-tools/lsp/color/init.lua
index 746dbbd..46e4fee 100644
--- a/lua/flutter-tools/lsp/color/init.lua
+++ b/lua/flutter-tools/lsp/color/init.lua
@@ -10,7 +10,7 @@ function M.document_color()
 
   local client = lsp_utils.get_dartls_client()
   if client and client.server_capabilities.colorProvider then
-    client.request("textDocument/documentColor", params, nil, 0)
+    client:request("textDocument/documentColor", params, nil, 0)
   end
 end
 
diff --git a/lua/flutter-tools/lsp/color/utils.lua b/lua/flutter-tools/lsp/color/utils.lua
index 2d15b99..db5c68c 100644
--- a/lua/flutter-tools/lsp/color/utils.lua
+++ b/lua/flutter-tools/lsp/color/utils.lua
@@ -109,7 +109,7 @@ end
 ---@param start_pos number
 ---@param end_pos number
 local function hl_range(bufnr, namespace, hlname, start_pos, end_pos)
-  local hl = vim.highlight
+  local hl = vim.hl
   hl.range(bufnr, namespace, hlname, start_pos, end_pos, { priority = hl.priorities.user })
 end
 
diff --git a/lua/flutter-tools/lsp/commands.lua b/lua/flutter-tools/lsp/commands.lua
index 22a7c97..b2f4fc1 100644
--- a/lua/flutter-tools/lsp/commands.lua
+++ b/lua/flutter-tools/lsp/commands.lua
@@ -19,7 +19,7 @@ function M.refactor_perform(command, ctx)
     prompt = "Enter a name for the variable: "
     default = "newVariable"
   else
-    client.request("workspace/executeCommand", command)
+    client:request("workspace/executeCommand", command)
     return
   end
 
@@ -34,7 +34,7 @@ function M.refactor_perform(command, ctx)
     -- see more: https://github.com/dart-lang/sdk/blob/e995cb5f7cd67d39c1ee4bdbe95c8241db36725f/pkg/analysis_server/lib/src/lsp/handlers/commands/perform_refactor.dart#L53
     local optionsIndex = 6
     command.arguments[optionsIndex] = { name = name }
-    client.request("workspace/executeCommand", command)
+    client:request("workspace/executeCommand", command)
   end)
 end
 
diff --git a/lua/flutter-tools/lsp/init.lua b/lua/flutter-tools/lsp/init.lua
index e95672d..7132b0c 100644
--- a/lua/flutter-tools/lsp/init.lua
+++ b/lua/flutter-tools/lsp/init.lua
@@ -119,15 +119,9 @@ local function get_defaults(opts)
     handlers = {
       -- TODO: can this be replaced with the initialized capability
       ["$/progress"] = handle_progress,
-      ["dart/textDocument/publishClosingLabels"] = utils.lsp_handler(
-        require("flutter-tools.labels").closing_tags
-      ),
-      ["dart/textDocument/publishOutline"] = utils.lsp_handler(
-        require("flutter-tools.outline").document_outline
-      ),
-      ["dart/textDocument/publishFlutterOutline"] = utils.lsp_handler(
-        require("flutter-tools.guides").widget_guides
-      ),
+      ["dart/textDocument/publishClosingLabels"] = require("flutter-tools.labels").closing_tags,
+      ["dart/textDocument/publishOutline"] = require("flutter-tools.outline").document_outline,
+      ["dart/textDocument/publishFlutterOutline"] = require("flutter-tools.guides").widget_guides,
       ["textDocument/documentColor"] = require("flutter-tools.lsp.color").on_document_color,
       ["dart/reanalyze"] = function() end, -- returns: None
       ["dart/textDocument/super"] = handle_super,
@@ -156,13 +150,15 @@ end
 
 function M.restart()
   local client = lsp_utils.get_dartls_client()
-  if client then
-    local bufs = lsp.get_buffers_by_client_id(client.id)
-    lsp.stop_client(client.id)
-    local client_id = lsp.start_client(client.config)
-    for _, buf in pairs(bufs) do
-      if client_id then lsp.buf_attach_client(buf, client_id) end
-    end
+  if not client then return end
+  local client_config = client.config
+  local bufs = vim.tbl_keys(client.attached_buffers)
+  client:stop()
+  -- `Client:stop()` marks the client as stopping synchronously, so the default
+  -- `reuse_client` predicate will not hand the dying client back to us here. The
+  -- first `start` spawns the replacement, the rest attach to it.
+  for _, buf in ipairs(bufs) do
+    if api.nvim_buf_is_valid(buf) then lsp.start(client_config, { bufnr = buf }) end
   end
 end
 
@@ -215,7 +211,7 @@ function M.dart_lsp_super()
       character = lsp_col, -- 0-based character position
     },
   }
-  client.request("dart/textDocument/super", params, nil, 0)
+  client:request("dart/textDocument/super", params, nil, 0)
 end
 
 function M.dart_reanalyze() lsp.buf_request(0, "dart/reanalyze") end
@@ -254,11 +250,7 @@ local function get_server_config(user_config, callback)
     config.commands = merge_config(defaults.commands, config.commands)
 
     config.on_init = function(client, _)
-      if vim.fn.has("nvim-0.12") == 0 then
-        return client.notify("workspace/didChangeConfiguration", { settings = config.settings })
-      else
-        return client:notify("workspace/didChangeConfiguration", { settings = config.settings })
-      end
+      return client:notify("workspace/didChangeConfiguration", { settings = config.settings })
     end
     callback(config)
   end)
diff --git a/lua/flutter-tools/lsp/rename.lua b/lua/flutter-tools/lsp/rename.lua
index 6b2e90a..b44a3f2 100644
--- a/lua/flutter-tools/lsp/rename.lua
+++ b/lua/flutter-tools/lsp/rename.lua
@@ -67,7 +67,7 @@ function M.rename(new_name, opts)
     local params = util.make_position_params(win, client.offset_encoding) --[[@as lsp.RenameParams]]
     params.newName = name
     local handler = client.handlers["textDocument/rename"] or lsp.handlers["textDocument/rename"]
-    client.request("textDocument/rename", params, function(...)
+    client:request("textDocument/rename", params, function(...)
       handler(...)
       if result then lsp.util.apply_workspace_edit(result, client.offset_encoding) end
 
@@ -93,7 +93,7 @@ function M.rename(new_name, opts)
         },
       }
 
-      client.request("workspace/willRenameFiles", params, function(err, result)
+      client:request("workspace/willRenameFiles", params, function(err, result)
         if err then
           ui.notify(err.message or "Error on getting lsp rename results!", ui.ERROR)
           return
@@ -106,9 +106,9 @@ function M.rename(new_name, opts)
   end
 
   -- Try to use prepare rename first
-  if client.supports_method("textDocument/prepareRename") then
+  if client:supports_method("textDocument/prepareRename") then
     local params = util.make_position_params(win, client.offset_encoding)
-    client.request("textDocument/prepareRename", params, function(err, result)
+    client:request("textDocument/prepareRename", params, function(err, result)
       if err or result == nil then
         if err then
           ui.notify(("Error on prepareRename: %s"):format(err.message), ui.ERROR)
@@ -142,7 +142,7 @@ function M.rename(new_name, opts)
       end)
     end, bufnr)
   else
-    assert(client.supports_method("textDocument/rename"), "Client must support textDocument/rename")
+    assert(client:supports_method("textDocument/rename"), "Client must support textDocument/rename")
     if new_name then
       rename_fix_imports(new_name)
       return
diff --git a/lua/flutter-tools/menu.lua b/lua/flutter-tools/menu.lua
index 943c7df..5e5adac 100644
--- a/lua/flutter-tools/menu.lua
+++ b/lua/flutter-tools/menu.lua
@@ -39,7 +39,7 @@ local function command_entry_maker(max_width)
     })
 
     local items = { { en.label, "Type" } }
-    if has_hint then table.insert(items, { en.hint, "Comment" }) end
+    if has_hint then table.insert(items, { en.hint, ui.DIM_HL }) end
     return displayer(items)
   end
   return function(entry)
diff --git a/lua/flutter-tools/outline.lua b/lua/flutter-tools/outline.lua
index 6581124..1feb982 100644
--- a/lua/flutter-tools/outline.lua
+++ b/lua/flutter-tools/outline.lua
@@ -56,7 +56,7 @@ local icon_highlights = {
   [icons.GETTER] = { name = "Getter", link = "Function" },
   [icons.ENUM] = { name = "Enum", link = "Type" },
   [icons.ENUM_CONSTANT] = { name = "EnumConstant", link = "Type" },
-  [icons.DEFAULT] = { name = "Default", link = "Comment" },
+  [icons.DEFAULT] = { name = "Default", link = ui.DIM_HL },
 }
 
 api.nvim_set_hl(0, MARKER_HL, { default = true, link = "NonText" })
@@ -149,7 +149,7 @@ local function parse_outline(result, node, indent, marker)
   local length = #table.concat(display_str, " ")
 
   local return_type = element.returnType and element.returnType .. " "
-  length = add_segment(text, hl, return_type, "Comment", length)
+  length = add_segment(text, hl, return_type, ui.DIM_HL, length)
   length = add_segment(text, hl, element.name, "None", length)
   length = add_segment(text, hl, element.typeParameters, "Type", length)
   length = add_segment(text, hl, element.parameters, "Bold", length)
diff --git a/lua/flutter-tools/ui.lua b/lua/flutter-tools/ui.lua
index 8067be1..99ee37a 100644
--- a/lua/flutter-tools/ui.lua
+++ b/lua/flutter-tools/ui.lua
@@ -30,6 +30,16 @@ local api = vim.api
 local namespace_id = api.nvim_create_namespace("flutter_tools_popups")
 M.entry_type = entry_type
 
+---Highlight group for de-emphasised text (closing tags, outline chrome, menu hints).
+---Nvim 0.13 ships a core `Dimmed` group for exactly this; below that we fall back to
+---`Comment`, which is what `Dimmed` itself links to by default. Declared with
+---`default = true` so a colorscheme or user definition always wins.
+M.DIM_HL = "FlutterToolsDimmed"
+utils.highlight(M.DIM_HL, {
+  default = true,
+  link = vim.fn.has("nvim-0.13") == 1 and "Dimmed" or "Comment",
+})
+
 function M.clear_highlights(buf_id, ns_id, line_start, line_end)
   line_start = line_start or 0
   line_end = line_end or -1
@@ -44,14 +54,14 @@ function M.add_highlights(buf_id, lines, ns_id)
   ns_id = ns_id or namespace_id
   if not lines then return end
   for _, line in ipairs(lines) do
-    api.nvim_buf_add_highlight(
-      buf_id,
-      ns_id,
-      line.highlight,
-      line.line_number,
-      line.column_start,
-      line.column_end
-    )
+    -- NOTE: `strict = false` so an end column past the end of the line is clamped
+    -- rather than raising, matching the behaviour callers relied on previously.
+    api.nvim_buf_set_extmark(buf_id, ns_id, line.line_number, line.column_start, {
+      end_row = line.line_number,
+      end_col = line.column_end,
+      hl_group = line.highlight,
+      strict = false,
+    })
   end
 end
 
diff --git a/lua/flutter-tools/utils/init.lua b/lua/flutter-tools/utils/init.lua
index 29c69d5..0a5e213 100644
--- a/lua/flutter-tools/utils/init.lua
+++ b/lua/flutter-tools/utils/init.lua
@@ -3,7 +3,6 @@ local fn = vim.fn
 local api = vim.api
 
 local lazy = require("flutter-tools.lazy")
-local path = lazy.require("flutter-tools.utils.path") ---@module "flutter-tools.utils.path"
 
 --- if every item in a table is an empty value return true
 function M.list_is_empty(tbl)
@@ -82,54 +81,13 @@ function M.executable(bin) return fn.executable(bin) > 0 end
 ---Get the attribute value of a specified highlight
 ---@param name string
 ---@param attribute string
----@return string?
-function M.get_hl(name, attribute)
-  if api.nvim_get_hl then
-    local hl = api.nvim_get_hl(0, { name = name })
-    return hl[attribute]
-  else
-    local ok, hl = pcall(api.nvim_get_hl_by_name, name, true)
-    if not ok then return end
-    hl.foreground = hl.foreground and "#" .. bit.tohex(hl.foreground, 6)
-    hl.background = hl.background and "#" .. bit.tohex(hl.background, 6)
-    local attr = ({ bg = "background", fg = "foreground" })[attribute] or attribute
-    return hl[attr]
-  end
-end
-
-function M.open_command()
-  if path.is_mac then return "open", {} end
-  if path.is_linux then return "xdg-open", {} end
-  if path.is_windows then return "cmd.exe", { "/c", "start" } end
-  return nil, nil
-end
+---@return string|integer|boolean|nil
+function M.get_hl(name, attribute) return api.nvim_get_hl(0, { name = name })[attribute] end
 
 ---@param lines string[]
 ---@return string
 function M.join(lines) return table.concat(lines, "\n") end
 
----Create an lsp handler compatible with the new handler signature
----see: https://github.com/neovim/neovim/pull/15504/
----@param func function
----@return function
-function M.lsp_handler(func)
-  return function(...)
-    local config_or_client_id = select(4, ...)
-    local is_new = type(config_or_client_id) ~= "number"
-    if is_new then
-      func(...)
-    else
-      local err = select(1, ...)
-      local method = select(2, ...)
-      local result = select(3, ...)
-      local client_id = select(4, ...)
-      local bufnr = select(5, ...)
-      local config = select(6, ...)
-      func(err, result, { method = method, client_id = client_id, bufnr = bufnr }, config)
-    end
-  end
-end
-
 ---@enum Events
 M.events = {
   PROJECT_CONFIG_CHANGED = "FlutterToolsProjectConfigChanged",