diff --git a/doc/cp.txt b/doc/cp.txt
index bb0f0f4..f730423 100644
--- a/doc/cp.txt
+++ b/doc/cp.txt
@@ -148,6 +148,7 @@ Here's an example configuration with lazy.nvim: >lua
             scrapers = { 'atcoder', 'codeforces', 'cses' },
             filename = default_filename,  -- <contest id> + <problem id>
             run_panel = {
+                ansi = true,
                 diff_mode = 'vim',
                 next_test_key = '<c-n>',
                 prev_test_key = '<c-p>',
@@ -199,6 +200,12 @@ Here's an example configuration with lazy.nvim: >lua
 
                                                         *cp.RunPanelConfig*
     Fields: ~
+        {ansi}            (boolean, default: true) Enable ANSI color parsing and
+                          highlighting. When true, compiler output and test results
+                          display with colored syntax highlighting. When false,
+                          ANSI escape codes are stripped for plain text display.
+                          Requires vim.g.terminal_color_* to be configured for
+                          proper color display.
         {diff_mode}       (string, default: "vim") Diff backend: "vim" or "git".
                           Git provides character-level precision, vim uses
                           built-in diff.
diff --git a/lua/cp/ansi.lua b/lua/cp/ansi.lua
index d8116f0..c8e2a01 100644
--- a/lua/cp/ansi.lua
+++ b/lua/cp/ansi.lua
@@ -4,6 +4,8 @@
 
 local M = {}
 
+local logger = require('cp.log')
+
 ---@param raw_output string|table
 ---@return string
 function M.bytes_to_string(raw_output)
@@ -192,6 +194,21 @@ function M.setup_highlight_groups()
     BrightWhite = vim.g.terminal_color_15,
   }
 
+  local missing_color = false
+  for _, terminal_color in pairs(color_map) do
+    if terminal_color == nil then
+      missing_color = true
+      break
+    end
+  end
+
+  if missing_color or #color_map == 0 then
+    logger.log(
+      'ansi terminal colors (vim.g.terminal_color_*) not configured. . ANSI colors will not display properly. ',
+      vim.log.levels.WARN
+    )
+  end
+
   local combinations = {
     { bold = false, italic = false },
     { bold = true, italic = false },
@@ -202,7 +219,7 @@ function M.setup_highlight_groups()
   for _, combo in ipairs(combinations) do
     for color_name, terminal_color in pairs(color_map) do
       local parts = { 'CpAnsi' }
-      local opts = { fg = terminal_color }
+      local opts = { fg = terminal_color or 'NONE' }
 
       if combo.bold then
         table.insert(parts, 'Bold')
diff --git a/lua/cp/config.lua b/lua/cp/config.lua
index 1a52a5c..a1564fd 100644
--- a/lua/cp/config.lua
+++ b/lua/cp/config.lua
@@ -30,6 +30,7 @@
 ---@field setup_code? fun(ctx: ProblemContext)
 
 ---@class RunPanelConfig
+---@field ansi boolean Enable ANSI color parsing and highlighting
 ---@field diff_mode "vim"|"git" Diff backend to use
 ---@field next_test_key string Key to navigate to next test case
 ---@field prev_test_key string Key to navigate to previous test case
@@ -97,6 +98,7 @@ M.defaults = {
   scrapers = constants.PLATFORMS,
   filename = nil,
   run_panel = {
+    ansi = true,
     diff_mode = 'vim',
     next_test_key = '<c-n>',
     prev_test_key = '<c-p>',
@@ -186,6 +188,11 @@ function M.setup(user_config)
   })
 
   vim.validate({
+    ansi = {
+      config.run_panel.ansi,
+      'boolean',
+      'ansi color parsing must be enabled xor disabled',
+    },
     diff_mode = {
       config.run_panel.diff_mode,
       function(value)
diff --git a/lua/cp/init.lua b/lua/cp/init.lua
index 2e3a742..7560f01 100644
--- a/lua/cp/init.lua
+++ b/lua/cp/init.lua
@@ -8,7 +8,7 @@ local scrape = require('cp.scrape')
 local snippets = require('cp.snippets')
 
 if not vim.fn.has('nvim-0.10.0') then
-  vim.notify('[cp.nvim]: requires nvim-0.10.0+', vim.log.levels.ERROR)
+  logger.log('[cp.nvim]: requires nvim-0.10.0+', vim.log.levels.ERROR)
   return {}
 end
 
@@ -537,8 +537,10 @@ local function toggle_run_panel(is_debug)
   refresh_run_panel()
 
   vim.schedule(function()
-    local ansi = require('cp.ansi')
-    ansi.setup_highlight_groups()
+    if config.run_panel.ansi then
+      local ansi = require('cp.ansi')
+      ansi.setup_highlight_groups()
+    end
     if current_diff_layout then
       update_diff_panes()
     end
diff --git a/lua/cp/run.lua b/lua/cp/run.lua
index 3303cbd..ddd2346 100644
--- a/lua/cp/run.lua
+++ b/lua/cp/run.lua
@@ -241,9 +241,13 @@ local function run_single_test_case(ctx, contest_config, cp_config, test_case)
   local actual_highlights = {}
 
   if actual_output ~= '' then
-    local parsed = ansi.parse_ansi_text(actual_output)
-    actual_output = table.concat(parsed.lines, '\n')
-    actual_highlights = parsed.highlights
+    if cp_config.run_panel.ansi then
+      local parsed = ansi.parse_ansi_text(actual_output)
+      actual_output = table.concat(parsed.lines, '\n')
+      actual_highlights = parsed.highlights
+    else
+      actual_output = actual_output:gsub('\027%[[%d;]*[a-zA-Z]', '')
+    end
   end
 
   local max_lines = cp_config.run_panel.max_output_lines
@@ -362,11 +366,18 @@ end
 
 function M.handle_compilation_failure(compilation_output)
   local ansi = require('cp.ansi')
+  local config = require('cp.config').setup()
 
-  -- Always parse the compilation output - it contains everything now
-  local parsed = ansi.parse_ansi_text(compilation_output or '')
-  local clean_text = table.concat(parsed.lines, '\n')
-  local highlights = parsed.highlights
+  local clean_text
+  local highlights = {}
+
+  if config.run_panel.ansi then
+    local parsed = ansi.parse_ansi_text(compilation_output or '')
+    clean_text = table.concat(parsed.lines, '\n')
+    highlights = parsed.highlights
+  else
+    clean_text = (compilation_output or ''):gsub('\027%[[%d;]*[a-zA-Z]', '')
+  end
 
   for _, test_case in ipairs(run_panel_state.test_cases) do
     test_case.status = 'fail'
diff --git a/spec/ansi_spec.lua b/spec/ansi_spec.lua
index 0b7faf8..ff7a96b 100644
--- a/spec/ansi_spec.lua
+++ b/spec/ansi_spec.lua
@@ -212,4 +212,33 @@ describe('ansi parser', function()
       assert.is_nil(state.foreground)
     end)
   end)
+
+  describe('setup_highlight_groups', function()
+    it('creates highlight groups with fallback colors when terminal colors are nil', function()
+      local original_colors = {}
+      for i = 0, 15 do
+        original_colors[i] = vim.g['terminal_color_' .. i]
+        vim.g['terminal_color_' .. i] = nil
+      end
+
+      ansi.setup_highlight_groups()
+
+      local highlight = vim.api.nvim_get_hl(0, { name = 'CpAnsiRed' })
+      -- When 'NONE' is set, nvim_get_hl returns nil for that field
+      assert.is_nil(highlight.fg)
+
+      for i = 0, 15 do
+        vim.g['terminal_color_' .. i] = original_colors[i]
+      end
+    end)
+
+    it('creates highlight groups with proper colors when terminal colors are set', function()
+      vim.g.terminal_color_1 = '#ff0000'
+
+      ansi.setup_highlight_groups()
+
+      local highlight = vim.api.nvim_get_hl(0, { name = 'CpAnsiRed' })
+      assert.equals(0xff0000, highlight.fg)
+    end)
+  end)
 end)
diff --git a/spec/config_spec.lua b/spec/config_spec.lua
index 7fc049b..8c4c79c 100644
--- a/spec/config_spec.lua
+++ b/spec/config_spec.lua
@@ -81,6 +81,16 @@ describe('cp.config', function()
     end)
 
     describe('run_panel config validation', function()
+      it('validates ansi is boolean', function()
+        local invalid_config = {
+          run_panel = { ansi = 'invalid' },
+        }
+
+        assert.has_error(function()
+          config.setup(invalid_config)
+        end, 'ansi: expected ansi color parsing must be enabled xor disabled, got string')
+      end)
+
       it('validates diff_mode values', function()
         local invalid_config = {
           run_panel = { diff_mode = 'invalid' },
@@ -114,6 +124,7 @@ describe('cp.config', function()
       it('accepts valid run_panel config', function()
         local valid_config = {
           run_panel = {
+            ansi = false,
             diff_mode = 'git',
             next_test_key = 'j',
             prev_test_key = 'k',
diff --git a/spec/extmark_spec.lua b/spec/extmark_spec.lua
new file mode 100644
index 0000000..6383d55
--- /dev/null
+++ b/spec/extmark_spec.lua
@@ -0,0 +1,215 @@
+describe('extmarks', function()
+  local spec_helper = require('spec.spec_helper')
+  local highlight
+
+  before_each(function()
+    spec_helper.setup()
+    highlight = require('cp.highlight')
+  end)
+
+  after_each(function()
+    spec_helper.teardown()
+  end)
+
+  describe('buffer deletion', function()
+    it('clears namespace on buffer delete', function()
+      local bufnr = 1
+      local namespace = 100
+      local mock_clear = stub(vim.api, 'nvim_buf_clear_namespace')
+      local mock_extmark = stub(vim.api, 'nvim_buf_set_extmark')
+
+      highlight.apply_highlights(bufnr, {
+        {
+          line = 0,
+          col_start = 0,
+          col_end = 5,
+          highlight_group = 'CpDiffAdded',
+        },
+      }, namespace)
+
+      assert.stub(mock_clear).was_called_with(bufnr, namespace, 0, -1)
+      mock_clear:revert()
+      mock_extmark:revert()
+    end)
+
+    it('handles invalid buffer gracefully', function()
+      local bufnr = 999
+      local namespace = 100
+      local mock_clear = stub(vim.api, 'nvim_buf_clear_namespace')
+      local mock_extmark = stub(vim.api, 'nvim_buf_set_extmark')
+
+      mock_clear.on_call_with(bufnr, namespace, 0, -1).invokes(function()
+        error('Invalid buffer')
+      end)
+
+      local success = pcall(highlight.apply_highlights, bufnr, {
+        {
+          line = 0,
+          col_start = 0,
+          col_end = 5,
+          highlight_group = 'CpDiffAdded',
+        },
+      }, namespace)
+
+      assert.is_false(success)
+      mock_clear:revert()
+      mock_extmark:revert()
+    end)
+  end)
+
+  describe('namespace isolation', function()
+    it('creates unique namespaces', function()
+      local mock_create = stub(vim.api, 'nvim_create_namespace')
+      mock_create.on_call_with('cp_diff_highlights').returns(100)
+      mock_create.on_call_with('cp_test_list').returns(200)
+      mock_create.on_call_with('cp_ansi_highlights').returns(300)
+
+      local diff_ns = highlight.create_namespace()
+      local test_ns = vim.api.nvim_create_namespace('cp_test_list')
+      local ansi_ns = vim.api.nvim_create_namespace('cp_ansi_highlights')
+
+      assert.equals(100, diff_ns)
+      assert.equals(200, test_ns)
+      assert.equals(300, ansi_ns)
+
+      mock_create:revert()
+    end)
+
+    it('clears specific namespace independently', function()
+      local bufnr = 1
+      local ns1 = 100
+      local ns2 = 200
+      local mock_clear = stub(vim.api, 'nvim_buf_clear_namespace')
+      local mock_extmark = stub(vim.api, 'nvim_buf_set_extmark')
+
+      highlight.apply_highlights(bufnr, {
+        { line = 0, col_start = 0, col_end = 5, highlight_group = 'CpDiffAdded' },
+      }, ns1)
+
+      highlight.apply_highlights(bufnr, {
+        { line = 1, col_start = 0, col_end = 3, highlight_group = 'CpDiffRemoved' },
+      }, ns2)
+
+      assert.stub(mock_clear).was_called_with(bufnr, ns1, 0, -1)
+      assert.stub(mock_clear).was_called_with(bufnr, ns2, 0, -1)
+      assert.stub(mock_clear).was_called(2)
+
+      mock_clear:revert()
+      mock_extmark:revert()
+    end)
+  end)
+
+  describe('multiple updates', function()
+    it('clears previous extmarks on each update', function()
+      local bufnr = 1
+      local namespace = 100
+      local mock_clear = stub(vim.api, 'nvim_buf_clear_namespace')
+      local mock_extmark = stub(vim.api, 'nvim_buf_set_extmark')
+
+      highlight.apply_highlights(bufnr, {
+        { line = 0, col_start = 0, col_end = 5, highlight_group = 'CpDiffAdded' },
+      }, namespace)
+
+      highlight.apply_highlights(bufnr, {
+        { line = 1, col_start = 0, col_end = 3, highlight_group = 'CpDiffRemoved' },
+      }, namespace)
+
+      assert.stub(mock_clear).was_called(2)
+      assert.stub(mock_clear).was_called_with(bufnr, namespace, 0, -1)
+      assert.stub(mock_extmark).was_called(2)
+
+      mock_clear:revert()
+      mock_extmark:revert()
+    end)
+
+    it('handles empty highlights', function()
+      local bufnr = 1
+      local namespace = 100
+      local mock_clear = stub(vim.api, 'nvim_buf_clear_namespace')
+      local mock_extmark = stub(vim.api, 'nvim_buf_set_extmark')
+
+      highlight.apply_highlights(bufnr, {
+        { line = 0, col_start = 0, col_end = 5, highlight_group = 'CpDiffAdded' },
+      }, namespace)
+
+      highlight.apply_highlights(bufnr, {}, namespace)
+
+      assert.stub(mock_clear).was_called(2)
+      assert.stub(mock_extmark).was_called(1)
+
+      mock_clear:revert()
+      mock_extmark:revert()
+    end)
+
+    it('skips invalid highlights', function()
+      local bufnr = 1
+      local namespace = 100
+      local mock_clear = stub(vim.api, 'nvim_buf_clear_namespace')
+      local mock_extmark = stub(vim.api, 'nvim_buf_set_extmark')
+
+      highlight.apply_highlights(bufnr, {
+        { line = 0, col_start = 5, col_end = 5, highlight_group = 'CpDiffAdded' },
+        { line = 1, col_start = 7, col_end = 3, highlight_group = 'CpDiffAdded' },
+        { line = 2, col_start = 0, col_end = 5, highlight_group = 'CpDiffAdded' },
+      }, namespace)
+
+      assert.stub(mock_clear).was_called_with(bufnr, namespace, 0, -1)
+      assert.stub(mock_extmark).was_called(1)
+      assert.stub(mock_extmark).was_called_with(bufnr, namespace, 2, 0, {
+        end_col = 5,
+        hl_group = 'CpDiffAdded',
+        priority = 100,
+      })
+
+      mock_clear:revert()
+      mock_extmark:revert()
+    end)
+  end)
+
+  describe('error handling', function()
+    it('fails when clear_namespace fails', function()
+      local bufnr = 1
+      local namespace = 100
+      local mock_clear = stub(vim.api, 'nvim_buf_clear_namespace')
+      local mock_extmark = stub(vim.api, 'nvim_buf_set_extmark')
+
+      mock_clear.on_call_with(bufnr, namespace, 0, -1).invokes(function()
+        error('Namespace clear failed')
+      end)
+
+      local success = pcall(highlight.apply_highlights, bufnr, {
+        { line = 0, col_start = 0, col_end = 5, highlight_group = 'CpDiffAdded' },
+      }, namespace)
+
+      assert.is_false(success)
+      assert.stub(mock_extmark).was_not_called()
+
+      mock_clear:revert()
+      mock_extmark:revert()
+    end)
+  end)
+
+  describe('parse_and_apply_diff cleanup', function()
+    it('clears namespace before applying parsed diff', function()
+      local bufnr = 1
+      local namespace = 100
+      local mock_clear = stub(vim.api, 'nvim_buf_clear_namespace')
+      local mock_extmark = stub(vim.api, 'nvim_buf_set_extmark')
+      local mock_set_lines = stub(vim.api, 'nvim_buf_set_lines')
+      local mock_get_option = stub(vim.api, 'nvim_get_option_value')
+      local mock_set_option = stub(vim.api, 'nvim_set_option_value')
+
+      mock_get_option.returns(false)
+
+      highlight.parse_and_apply_diff(bufnr, '+hello {+world+}', namespace)
+
+      assert.stub(mock_clear).was_called_with(bufnr, namespace, 0, -1)
+
+      mock_clear:revert()
+      mock_extmark:revert()
+      mock_set_lines:revert()
+      mock_get_option:revert()
+      mock_set_option:revert()
+    end)
+  end)
+end)
diff --git a/spec/run_spec.lua b/spec/run_spec.lua
new file mode 100644
index 0000000..e70f4f7
--- /dev/null
+++ b/spec/run_spec.lua
@@ -0,0 +1,27 @@
+describe('run module', function()
+  local run = require('cp.run')
+
+  describe('basic functionality', function()
+    it('has required functions', function()
+      assert.is_function(run.load_test_cases)
+      assert.is_function(run.run_test_case)
+      assert.is_function(run.run_all_test_cases)
+      assert.is_function(run.get_run_panel_state)
+      assert.is_function(run.handle_compilation_failure)
+    end)
+
+    it('can get panel state', function()
+      local state = run.get_run_panel_state()
+      assert.is_table(state)
+      assert.is_table(state.test_cases)
+    end)
+
+    it('handles compilation failure', function()
+      local compilation_output = 'error.cpp:1:1: error: undefined variable'
+
+      assert.does_not_error(function()
+        run.handle_compilation_failure(compilation_output)
+      end)
+    end)
+  end)
+end)