diff --git a/README.md b/README.md
index 5611c97..09c1528 100644
--- a/README.md
+++ b/README.md
@@ -15,7 +15,7 @@ that information can be useful. For example, in statuslines and the tabline.
     - [Using mini.deps and mini.statusline](#using-minideps-and-ministatusline)
   - [Configuration](#configuration)
     - [Formatters](#formatters)
-      - [The "extended" built-in](#the-extended-built-in)
+      - [The "default" built-in](#the-default-built-in)
       - [The "short" built-in](#the-short-built-in)
       - [Customize a built-in](#customize-a-built-in)
       - [Use a custom formatter](#use-a-custom-formatter)
@@ -39,6 +39,8 @@ that information can be useful. For example, in statuslines and the tabline.
 ![1710925071](https://github.com/abeldekat/harpoonline/assets/58370433/4b911ed1-428d-4a64-ba9d-f67ba6438ce7)
 *Custom statusline in NvChad v2.5*
 
+*Note*: The video demonstrates the first release and will become outdated.
+
 ## Features
 
 - Supports multiple [harpoon2] lists.
@@ -101,7 +103,7 @@ local function config()
     if MiniStatusline.is_truncated(args.trunc_width) or isnt_normal_buffer() then
       return ""
     end
-    return Harpoonline.format() ---->  produce the info
+    return Harpoonline.format()
   end
   local function active() -- Hook, see mini.statusline setup
     -- copy any lines from mini.statusline, H.default_content_active:
@@ -140,42 +142,37 @@ The following configuration is implied when calling `setup` without arguments:
 ```lua
 ---@class HarpoonLineConfig
 Harpoonline.config = {
-  -- other nice icons: "󰀱", "", "󱡅"
+  -- other nice icons: "󰀱", "", "󱡅", "󰛢"
   ---@type string
   icon = '󰀱', -- An empty string disables showing the icon
 
-  -- Harpoon:list(), without a name, retrieves the default list:
+  -- Harpoon:list(), when name is nil, retrieves the default list:
   -- default_list_name: Configures the display name for the default list.
   ---@type string
   default_list_name = '',
 
-  ---@type "extended" | "short"
-  formatter = 'extended', -- use a built-in formatter
+  ---@type "default" | "short"
+  formatter = 'default', -- use a built-in formatter
 
   formatter_opts = {
-    extended = {
-      -- An indicator corresponds to a position in the harpoon list
-      -- Suggestion: Add an indicator for each configured "select" keybinding
-      indicators = { ' 1 ', ' 2 ', ' 3 ', ' 4 ' },
-      active_indicators = { '[1]', '[2]', '[3]', '[4]' },
-
-      -- 1 More indicators than items in the harpoon list:
-      empty_slot = '', -- ' · ', -- middledot. Disable using empty string
-
-      -- 2 Less indicators than items in the harpoon list
-      more_marks_indicator = ' … ', -- horizontal elipsis. Disable using empty string
-      more_marks_active_indicator = '[…]', -- Disable using empty string
+    default = {
+      inactive = ' %s ', -- including spaces
+      active = '[%s]',
+      -- Max number of slots to display:
+      max_slots = 4, -- Suggestion: as many as there are "select" keybindings
+      -- The number of items in the harpoon list exceeds max_slots:
+      more = '…', -- horizontal elipsis. Disable using empty string
     },
     short = {
       inner_separator = '|',
     },
   },
 
-  ---@type fun():string|nil
+  ---@type HarpoonlineFormatter
   custom_formatter = nil, -- use this formatter when configured
 
   ---@type fun()|nil
-  on_update = nil, -- optional action to perform after update
+  on_update = nil, -- Recommended: trigger the client when the line has been rebuild.
 }
 ```
 
@@ -188,9 +185,9 @@ Scenario's:
 - A: 3 marks, the current buffer is not harpooned
 - B: 3 marks, the current buffer is harpooned on mark 2
 
-#### The "extended" built-in
+#### The "default" built-in
 
-This is the default formatter. Default options: `config.formatter_opts.extended`
+Default options: `config.formatter_opts.default`
 
 Output A: :anchor:  ` 1  2  3 `
 
@@ -198,7 +195,7 @@ Output B: :anchor:  ` 1 [2] 3 `
 
 **Note**: Five marks, the fifth mark is the active buffer:
 
-Output B: 󰛢  ` 1  2  3  4 […] `
+Output B: :anchor:  ` 1  2  3  4 […] `
 
 #### The "short" built-in
 
@@ -212,66 +209,90 @@ Output B: :anchor:  `[2|3]`
 
 ```lua
 Harpoonline.setup({
-  -- formatter = "extended", -- configure the default formatter
+  -- config
   formatter_opts = {
-    extended = { -- remove all spaces...
-      indicators = { "1", "2", "3", "4" },
-      empty_slot = "·",
-      more_marks_indicator = "…", -- horizontal elipsis. Disable with empty string
-      more_marks_active_indicator = "[…]", -- Disable with empty string
+    default = { -- remove all spaces...
+      inactive = "%s",
+      active = "[%s]",
     },
   },
-  on_update = on_update,
+  -- more config
 })
 ```
 
-Output A: :anchor:  `123·`
+Output A: :anchor:  `123`
 
-Output B: :anchor:  `1[2]3·`
+Output B: :anchor:  `1[2]3`
 
 #### Use a custom formatter
 
 The following data is kept up-to-date internally, to be processed by formatters:
 
 ```lua
----@class HarpoonLineData
-H.data = {
-  -- Harpoon's default list is in use when list_name = nil
-  --- @type string|nil
-  list_name = nil, -- the name of the current list
-  --- @type number
-  list_length = 0, -- the length of the current list
-  --- @type number|nil
-  buffer_idx = nil, -- the mark of the current buffer if harpooned
-}
+---@class HarpoonlineData
+---@field list_name string|nil -- the name of the current list
+---@field items HarpoonItem[] -- the items of the current list
+---@field active_idx number|nil -- the harpoon index of the current buffer
 ```
 
-Example:
+Example "very short":
 
 ```lua
-local Harpoonline = require("harpoonline")
 Harpoonline.setup({
-  custom_formatter = Harpoonline.gen_formatter(
-    ---@param data HarpoonLineData
-    ---@return string
-    function(data)
-      return string.format( -- very short, without the length of the harpoon list
-        "%s%s%s",
-        "➡️ ",
-        data.list_name and string.format("%s ", data.list_name) or "",
-        data.buffer_idx and string.format("%d", data.buffer_idx) or "-"
-      )
-    end
-  ),
+  -- config
+  ---@param data HarpoonlineData
+  ---@param opts HarpoonLineConfig
+  ---@return string
+  custom_formatter = function(data,opts)
+    return string.format( -- very short, without the length of the harpoon list
+      "%s%s%s",
+      opts.icon .. " ",
+      data.list_name and string.format("%s ", data.list_name) or "",
+      data.active_idx and string.format("%d", data.active_idx) or "-"
+    )
+  end
+  -- more config
 })
 ```
 
-Output A: :arrow_right:  `-`
+Output A: :anchor:  `-`
 
-Output B: :arrow_right:  `2`
+Output B: :anchor:  `2`
+
+Example "letters":
+
+```lua
+Harpoonline.setup({
+  -- config
+  ---@param data HarpoonlineData
+  ---@param opts HarpoonLineConfig
+  ---@return string
+  custom_formatter = function(data, opts)
+    local letters = { "j", "k", "l", "h" }
+    local idx = data.active_idx
+    local slot = 0
+    local slots = vim.tbl_map(function(letter)
+      slot = slot + 1
+      return idx and idx == slot and string.upper(letter) or letter
+    end, vim.list_slice(letters, 1, math.min(#letters, #data.items)))
+
+    local name = data.list_name and data.list_name or opts.default_list_name
+    local header = string.format("%s%s%s", opts.icon, name == "" and "" or " ", name)
+    return header .. " " .. table.concat(slots)
+  end,
+  -- more config
+})
+```
+
+Output A: :anchor:  `jkl`
+
+Output B: :anchor:  `jKl`
+
+*Note*:
 
-*Note*: You can also use inner highlights in the formatter function.
+- You can also use inner highlights in the formatter function.
 See the example recipe for NvChad.
+- You can use the `harpoon` information inside each `data.items`
 
 ## Harpoon lists
 
@@ -413,7 +434,6 @@ return M
 
 - @theprimeagen: Harpoon is the most important part of my workflow.
 - @echasnovski: The structure of this plugin is heavily based on [mini.nvim]
-- @letieu: The `extended` formatter is inspired by plugin [harpoon-lualine]
 
 [harpoon2]: https://github.com/ThePrimeagen/harpoon/tree/harpoon2
 [mini.statusline]: https://github.com/echasnovski/mini.statusline
diff --git a/lua/harpoonline/init.lua b/lua/harpoonline/init.lua
index 846ac0f..6daccb1 100644
--- a/lua/harpoonline/init.lua
+++ b/lua/harpoonline/init.lua
@@ -1,4 +1,12 @@
--- Module definition ==========================================================
+-- Moddefinition ==========================================================
+
+---@class HarpoonlineData
+---@field list_name string|nil -- the name of the current list
+---@field items HarpoonItem[] -- the items of the current list
+---@field active_idx number|nil -- the harpoon index of the current buffer
+
+--The signature of a formatter function:
+---@alias HarpoonlineFormatter fun(data: HarpoonlineData, opts: HarpoonLineConfig): string
 
 ---@class HarpoonLine
 local Harpoonline = {}
@@ -10,13 +18,19 @@ Harpoonline.setup = function(config)
   if not has_harpoon then return end
 
   H.harpoon_plugin = Harpoon
+  H.apply_config(H.setup_config(config))
+
+  H.produce() -- initialize the line
+  if H.get_config().on_update then
+    local produce = H.produce
+    H.produce = function() -- composition: add on_update
+      produce()
+      H.get_config().on_update() -- notify clients
+    end
+  end
 
-  config = H.setup_config(config)
-  H.apply_config(config)
   H.create_autocommands()
-
   H.create_extensions(require('harpoon.extensions'))
-  H.initialize()
 end
 
 ---@class HarpoonLineConfig
@@ -25,91 +39,68 @@ Harpoonline.config = {
   ---@type string
   icon = '󰀱', -- An empty string disables showing the icon
 
-  -- Harpoon:list(), without a name, retrieves the default list:
+  -- Harpoon:list(), when name is nil, retrieves the default list:
   -- default_list_name: Configures the display name for the default list.
   ---@type string
   default_list_name = '',
 
-  ---@type "extended" | "short"
-  formatter = 'extended', -- use a builtin formatter
+  ---@type "default" | "short"
+  formatter = 'default', -- use a builtin formatter
 
   formatter_opts = {
-    extended = {
-      -- An indicator corresponds to a position in the harpoon list
-      -- Suggestion: Add an indicator for each configured "select" keybinding
-      indicators = { ' 1 ', ' 2 ', ' 3 ', ' 4 ' },
-      active_indicators = { '[1]', '[2]', '[3]', '[4]' },
-
-      -- 1 More indicators than items in the harpoon list:
-      empty_slot = '', -- ' · ', -- middledot. Disable using empty string
-
-      -- 2 Less indicators than items in the harpoon list
-      more_marks_indicator = ' … ', -- horizontal elipsis. Disable using empty string
-      more_marks_active_indicator = '[…]', -- Disable using empty string
+    default = {
+      inactive = ' %s ', -- including spaces
+      active = '[%s]',
+      -- Number of slots to display:
+      max_slots = 4, -- Suggestion: as many as there are "select" keybindings
+      -- The number of items in the harpoon list exceeds max_slots:
+      more = '…', -- horizontal elipsis. Disable using empty string
     },
     short = {
       inner_separator = '|',
     },
   },
 
-  ---@type fun():string|nil
+  ---@type HarpoonlineFormatter
   custom_formatter = nil, -- use this formatter when configured
 
   ---@type fun()|nil
-  on_update = nil, -- optional action to perform after update
+  on_update = nil, -- Recommended: trigger the client when the line has been rebuild.
 }
 
+-- Module functionality =======================================================
+
 ---@class HarpoonlineFormatterConfig
 Harpoonline.formatters = {
-  extended = function() return H.builtin_extended end,
+  default = function() return H.builtin_default end,
   short = function() return H.builtin_short end,
 }
 
--- Module functionality =======================================================
-
--- Given a formatter function, return a wrapper function that can be invoked
--- by consumers.
----@param formatter fun(data: HarpoonLineData):string
----@return function
-Harpoonline.gen_formatter = function(formatter)
-  return function() return formatter(H.data) end
-end
-
 -- Return true is the current buffer is harpooned, false otherwise
 -- Useful for extra highlighting
 ---@return boolean
-Harpoonline.is_buffer_harpooned = function() return H.data.buffer_idx ~= nil end
+Harpoonline.is_buffer_harpooned = function() return H.active_idx ~= nil end
 
 -- The function to be used by consumers
 ---@return string
-Harpoonline.format = function()
-  if not H.cached_result then H.cached_result = H.formatter and H.formatter() or '' end
-  return H.cached_result
-end
+Harpoonline.format = function() return H.cached_line end
 
 -- Helper data ================================================================
 
 H.harpoon_plugin = nil
 
+---@type HarpoonlineFormatter
+H.formatter = nil
+
 ---@type HarpoonLineConfig
 H.default_config = vim.deepcopy(Harpoonline.config)
 
----@class HarpoonLineData
-H.data = {
-  -- Harpoon's default list is in use when list_name = nil
-  --- @type string|nil
-  list_name = nil, -- the name of the current list
-  --- @type number
-  list_length = 0, -- the length of the current list
-  --- @type number|nil
-  buffer_idx = nil, -- the mark of the current buffer if harpooned
-}
-
--- @type string|nil
-H.cached_result = nil
-
----@type fun():string|nil
-H.formatter = nil
+---@type string
+H.cached_line = ''
+---@type string | nil
+H.list_name = nil
+---@type number | nil
+H.active_idx = nil
 
 -- Helper functionality =======================================================
 
@@ -131,17 +122,17 @@ end
 -- Sets the final config to use.
 -- If config.custom_formatter is configured, this will be the final formatter.
 -- Otherwise, use builtin config.formatter if its valid.
--- Otherwise, fallback to the "extended" builint formatter
+-- Otherwise, fallback to the "extended" builtin formatter
 ---@param config HarpoonLineConfig
 H.apply_config = function(config)
+  Harpoonline.config = config
+
   if config.custom_formatter then
     H.formatter = config.custom_formatter
   else
-    local is_valid = vim.tbl_contains(vim.tbl_keys(Harpoonline.formatters), config.formatter)
-    local key = is_valid and config.formatter or 'extended'
-    H.formatter = Harpoonline.gen_formatter(Harpoonline.formatters[key]())
+    local builtin = Harpoonline.formatters[config.formatter]
+    H.formatter = builtin and builtin() or H.builtin_default
   end
-  Harpoonline.config = config
 end
 
 ---@return HarpoonLineConfig
@@ -150,21 +141,21 @@ H.get_config = function() return Harpoonline.config end
 -- Update the data on each BufEnter event
 -- Update the name of the list on custom event HarpoonSwitchedList
 H.create_autocommands = function()
-  local augroup = vim.api.nvim_create_augroup('HarpoonLine', {})
+  local augroup = vim.api.nvim_create_augroup('Harpoonline', {})
 
   vim.api.nvim_create_autocmd('User', {
     group = augroup,
     pattern = 'HarpoonSwitchedList',
     callback = function(event)
-      H.data.list_name = event.data
-      H.update()
+      H.list_name = event.data
+      H.produce()
     end,
   })
 
   vim.api.nvim_create_autocmd({ 'BufEnter' }, {
     group = augroup,
     pattern = '*',
-    callback = H.update,
+    callback = H.produce,
   })
 end
 
@@ -172,20 +163,19 @@ end
 -- Needed because those actions can be done without leaving the buffer.
 -- All other update scenarios are covered by listening to the BufEnter event.
 H.create_extensions = function(Extensions)
-  H.harpoon_plugin:extend({ [Extensions.event_names.ADD] = H.update })
-  H.harpoon_plugin:extend({ [Extensions.event_names.REMOVE] = H.update })
+  H.harpoon_plugin:extend({ [Extensions.event_names.ADD] = H.produce })
+  H.harpoon_plugin:extend({ [Extensions.event_names.REMOVE] = H.produce })
 end
 
----@return HarpoonList
-H.get_list = function() return H.harpoon_plugin:list(H.data.list_name) end
-
 -- If the current buffer is harpooned, return the index of the harpoon mark
 -- Otherwise, return nil
 ---@param list HarpoonList
 ---@return number|nil
-H.buffer_idx = function(list)
+H.find_active_idx = function(list)
   if vim.bo.buftype ~= '' then return end -- not a normal buffer
-  if list:length() == 0 then return end -- no items in the list
+
+  -- if list:length() == 0 --  NOTE: Harpoon issue #555
+  if #list.items == 0 then return end -- no items in the list
 
   local current_file = vim.fn.expand('%:p:.')
   for idx, item in ipairs(list.items) do
@@ -193,23 +183,23 @@ H.buffer_idx = function(list)
   end
 end
 
----@param list HarpoonList
-H.update_data = function(list)
-  H.data.list_length = list:length()
-  H.data.buffer_idx = H.buffer_idx(list)
-end
-
 -- To be invoked on any harpoon-related event
 -- Performs action on_update if present
-H.update = function()
-  H.update_data(H.get_list())
-  H.cached_result = nil -- the format function should recompute
-
-  local on_update = H.get_config().on_update
-  if on_update then on_update() end
+H.produce = function()
+  ---@type HarpoonList
+  local list = H.harpoon_plugin:list(H.list_name)
+  H.active_idx = H.find_active_idx(list)
+
+  H.cached_line = H.formatter({
+    list_name = H.list_name,
+    -- list_length = list:length(), -- NOTE: Harpoon issue #555
+    items = list.items,
+    active_idx = H.active_idx,
+  }, H.get_config())
 end
 
-H.initialize = function() H.update_data(H.get_list()) end
+-- Returns the name of the list, or the configured default_list_name
+H.make_list_name = function(name) return name and name or H.get_config().default_list_name end
 
 -- Return either the icon or an empty string
 ---@return string
@@ -218,61 +208,46 @@ H.make_icon = function()
   return icon ~= '' and icon or ''
 end
 
----@param data HarpoonLineData
+---@param data HarpoonlineData
+---@param opts HarpoonLineConfig
 ---@return string
-H.builtin_short = function(data)
-  local opts = H.get_config().formatter_opts.short
+H.builtin_short = function(data, opts)
   local icon = H.make_icon()
-  local list_name = data.list_name and data.list_name or H.get_config().default_list_name
+  local list_name = H.make_list_name(data.list_name)
+
+  local o = opts.formatter_opts.short
   return string.format(
     '%s%s%s[%s%d]',
     icon,
     icon == '' and '' or ' ',
     list_name, -- no space after list name...
-    data.buffer_idx and string.format('%s%s', data.buffer_idx, opts.inner_separator) or '',
-    data.list_length
+    data.active_idx and string.format('%s%s', data.active_idx, o.inner_separator) or '',
+    #data.items
   )
 end
 
----@param data HarpoonLineData
+---@param data HarpoonlineData
+---@param opts HarpoonLineConfig
 ---@return string
-H.builtin_extended = function(data)
-  local opts = H.get_config().formatter_opts.extended
-  local show_empty_slots = opts.empty_slot and opts.empty_slot ~= ''
-
-  -- build prefix
-  local show_prefix = true -- show_empty_slots or data.number_of_tags > 0
-  local icon = H.make_icon()
-  local list_name = data.list_name and data.list_name or H.get_config().default_list_name
-  local prefix = not show_prefix and ''
-    or string.format(
-      '%s%s%s', --
-      icon,
-      list_name == '' and '' or ' ',
-      list_name
-    )
-
-  -- build slots
-  local nr_of_slots = #opts.indicators
-  local status = {}
-  for i = 1, nr_of_slots do
-    if i > data.list_length then -- more slots then ...
-      if show_empty_slots then table.insert(status, opts.empty_slot) end
-    elseif i == data.buffer_idx then
-      table.insert(status, opts.active_indicators[i])
-    else
-      table.insert(status, opts.indicators[i])
+H.builtin_default = function(data, opts)
+  local list_name = H.make_list_name(data.list_name)
+  local header = string.format('%s%s%s', H.make_icon(), list_name == '' and '' or ' ', list_name)
+
+  local o = opts.formatter_opts.default
+  local idx = data.active_idx
+  local slot = 0
+  local slots = vim.tbl_map(function()
+    slot = slot + 1
+    return string.format(idx and idx == slot and o.active or o.inactive, slot)
+  end, vim.list_slice(data.items, 1, math.min(o.max_slots, #data.items)))
+
+  if #data.items > o.max_slots then
+    if o.more and o.more ~= '' then
+      local fmt = idx and idx > o.max_slots and o.active or o.inactive
+      table.insert(slots, string.format(fmt, o.more))
     end
   end
-  -- add more marks indicator
-  if data.list_length > nr_of_slots then -- more marks then...
-    local ind = opts.more_marks_indicator
-    if data.buffer_idx and data.buffer_idx > nr_of_slots then ind = opts.more_marks_active_indicator end
-    if ind and ind ~= '' then table.insert(status, ind) end
-  end
-
-  prefix = prefix == '' and prefix or prefix .. ' '
-  return prefix .. table.concat(status)
+  return header .. (header == '' and '' or ' ') .. table.concat(slots)
 end
 
 return Harpoonline
diff --git a/tests/test_harpoonline.lua b/tests/test_harpoonline.lua
index 77281ba..496dcd5 100644
--- a/tests/test_harpoonline.lua
+++ b/tests/test_harpoonline.lua
@@ -76,77 +76,56 @@ T['format()'] = new_set()
 --          ╭─────────────────────────────────────────────────────────╮
 --          │                    Default formatter                    │
 --          ╰─────────────────────────────────────────────────────────╯
-T['format()']['extended'] = new_set()
-T['format()']['extended']['one harpoon'] = function()
+T['format()']['default'] = new_set()
+T['format()']['default']['one harpoon'] = function()
   child.lua([[M.setup()]])
   add_files_to_list({ '1' })
   eq(child.lua_get([[ M.format() ]]), icon .. ' [1]')
 end
-T['format()']['extended']['four harpoons'] = function()
+T['format()']['default']['four harpoons'] = function()
   child.lua([[M.setup()]])
   add_files_to_list({ '1', '2', '3', '4' })
   eq(child.lua_get([[ M.format() ]]), icon .. '  1  2  3 [4]')
 end
-T['format()']['extended']['six harpoons'] = function()
+T['format()']['default']['six harpoons'] = function()
   child.lua([[M.setup()]])
   add_files_to_list({ '1', '2', '3', '4', '5', '6' })
   eq(child.lua_get([[ M.format() ]]), icon .. '  1  2  3  4 [' .. more .. ']')
 end
-T['format()']['extended']['custom indicators'] = function()
+T['format()']['default']['more marks'] = function()
   child.lua([[
     M.setup({
-      formatter_opts = { extended = {
-        indicators = {"A", "B"}, active_indicators = {"-A-", "-B-"}
-      }}
-    })
-  ]])
-  add_files_to_list({ '1', '2' })
-  eq(child.lua_get([[ M.format() ]]), icon .. ' A-B-')
-end
-T['format()']['extended']['empty slots'] = function()
-  child.lua([[
-    M.setup({
-      formatter_opts = { extended = {
-        empty_slot = ' · '
-      }}
-    })
-  ]])
-  add_files_to_list({ '1', '2' })
-  eq(child.lua_get([[ M.format() ]]), icon .. '  1 [2] ·  · ')
-end
-T['format()']['extended']['more marks'] = function()
-  child.lua([[
-    M.setup({
-      formatter_opts = { extended = {
-        more_marks_indicator = '', more_marks_active_indicator = '',
+      formatter_opts = { default = {
+        more = ""
       }}
     })
   ]])
   add_files_to_list({ '1', '2', '3', '4', '5', '6' })
   eq(child.lua_get([[ M.format() ]]), icon .. '  1  2  3  4 ')
 end
-T['format()']['extended']['buffer not harpooned'] = function()
+T['format()']['default']['buffer not harpooned'] = function()
   child.lua([[M.setup()]])
   add_files_to_list({ '1', '2', '3', '4', '5' })
   edit('9')
   eq(child.lua_get([[ M.format() ]]), icon .. '  1  2  3  4  ' .. more .. ' ')
 end
-T['format()']['extended']['remove item'] = function()
+T['format()']['default']['remove item'] = function()
   child.lua([[M.setup()]])
   add_files_to_list({ '1', '2', '3' })
   child.lua([[ require("harpoon"):list():remove_at(3) ]])
   eq(child.lua_get([[ M.format() ]]), icon .. '  1  2 ')
 end
-T['format()']['extended']['remove all items'] = function()
+T['format()']['default']['remove all items'] = function()
   child.lua([[M.setup()]])
   add_files_to_list({ '1', '2' })
   child.lua([[ require("harpoon"):list():remove_at(2) ]])
   child.lua([[ require("harpoon"):list():remove_at(1) ]])
-  eq(child.lua_get([[ M.format() ]]), icon .. '  1 ') -- should be empty
+  eq(child.lua_get([[ M.format() ]]), icon .. ' ') -- should be empty
 
-  MiniTest.add_note('Incorrect, not empty!  See harpoon issue #555')
+  -- eq(child.lua_get([[ M.format() ]]), icon .. '  1 ') -- should be empty
+  -- MiniTest.add_note('Incorrect, not empty!  See harpoon issue #555')
 end
-T['format()']['extended']['switch list'] = function()
+T['format()']['default']['switch list'] = function()
   child.lua([[M.setup()]])
   add_files_to_list({ '1', '2' }, 'dev')
   child.lua([[
@@ -156,7 +135,7 @@ T['format()']['extended']['switch list'] = function()
   ]])
   eq(child.lua_get([[ M.format() ]]), icon .. ' dev  1 [2]')
 end
-T['format()']['extended']['default_list_name'] = function()
+T['format()']['default']['default_list_name'] = function()
   child.lua([[M.setup({default_list_name="mainlist"})]])
   add_files_to_list({ '1', '2' })
   eq(child.lua_get([[ M.format() ]]), icon .. ' mainlist  1 [2]')
@@ -215,16 +194,14 @@ end
 T['format()']['custom'] = function()
   child.lua([[
     M.setup({
-      custom_formatter = M.gen_formatter(
-        function(data)
-          return string.format("%s%s%s%s",
-            "Harpoonline: ",
-            data.buffer_idx and "Buffer is harpooned " or "Buffer is not harpooned ",
-            "in list ",
-            data.list_name and data.list_name or "default"
-          )
-        end
-      )
+      custom_formatter = function(data, _)
+        return string.format("%s%s%s%s",
+          "Harpoonline: ",
+          data.active_idx and "Buffer is harpooned " or "Buffer is not harpooned ",
+          "in list ",
+          data.list_name and data.list_name or "default"
+        )
+      end
     })
   ]])
   add_files_to_list({ '1', '2' })