diff --git a/.github/workflows/lint.yml b/.github/workflows/lint.yml
new file mode 100644
index 0000000..54e0686
--- /dev/null
+++ b/.github/workflows/lint.yml
@@ -0,0 +1,23 @@
+name: Lint
+on: [push, pull_request]
+jobs:
+  stylua:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: Check formatting
+        uses: JohnnyMorganz/stylua-action@v5
+        with:
+          token: ${{ secrets.GITHUB_TOKEN }}
+          # Keep in sync with the rev in .pre-commit-config.yaml.
+          version: 2.5.2
+          args: --check .
+
+  luacheck:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: Lint
+        uses: lunarmodules/luacheck@v1
+        with:
+          args: .
diff --git a/.luacheckrc b/.luacheckrc
new file mode 100644
index 0000000..bf470d4
--- /dev/null
+++ b/.luacheckrc
@@ -0,0 +1,44 @@
+-- Luacheck configuration for md-render.nvim
+-- Docs: https://luacheck.readthedocs.io/en/stable/config.html
+
+-- Neovim embeds LuaJIT.
+std = "luajit"
+cache = true
+
+-- Globals injected at runtime by Neovim and optional integrations.
+read_globals = {
+  "vim",
+  "Snacks", -- folke/snacks.nvim (optional image backend)
+}
+
+-- `vim.<subtable>.foo = ...` assignments are legitimate. Declaring the mutable
+-- subtables as writable globals stops luacheck reporting them as writes to a
+-- read-only field of the `vim` global.
+globals = {
+  "vim.g",
+  "vim.b",
+  "vim.w",
+  "vim.o",
+  "vim.bo",
+  "vim.wo",
+  "vim.go",
+  "vim.env",
+  "vim.opt",
+}
+
+-- Line width is owned by StyLua (column_width in .stylua.toml). A few string
+-- literals legitimately exceed it and cannot be wrapped.
+ignore = { "631" }
+
+exclude_files = { "tests/fixtures/" }
+
+-- Tests intentionally destructure unused return values, shadow module upvalues,
+-- and monkeypatch vim.* functions when mocking.
+files["tests/"] = {
+  ignore = {
+    "211", -- unused local variable
+    "212", -- unused argument
+    "431", -- shadowing an upvalue
+    "122", -- setting a read-only field of vim (mocking vim.notify, vim.api.*)
+  },
+}
diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
new file mode 100644
index 0000000..ca3ce19
--- /dev/null
+++ b/.pre-commit-config.yaml
@@ -0,0 +1,17 @@
+# Pre-commit hooks for md-render.nvim.
+# Setup:  pipx install pre-commit  (or: brew install pre-commit)
+#         pre-commit install
+# Run against everything:  pre-commit run --all-files
+#
+# Only StyLua runs here. It downloads its own release binary, so the hook needs no
+# local toolchain and formats staged Lua files in place (honoring .stylua.toml).
+#
+# Luacheck is intentionally CI-only (.github/workflows/lint.yml): its distribution
+# can't run cleanly on every local setup (e.g. the official language:lua hook fails
+# to build under Lua 5.5, and the Docker image is amd64-only). CI runs it on every
+# push / PR, which is enough to guard the lint gate.
+repos:
+  - repo: https://github.com/JohnnyMorganz/StyLua
+    rev: v2.5.2
+    hooks:
+      - id: stylua-github
diff --git a/Makefile b/Makefile
index 4ec36e4..dda2497 100644
--- a/Makefile
+++ b/Makefile
@@ -2,9 +2,19 @@ NVIM := nvim --headless -u NONE --noplugin
 
 TEST_FILES := $(sort $(wildcard tests/*_test.lua))
 
-.PHONY: test $(TEST_FILES)
+.PHONY: test $(TEST_FILES) lint format check
 
 test: $(TEST_FILES)
 
 $(TEST_FILES):
 	$(NVIM) -l $@
+
+# Format Lua sources in place (honors .stylua.toml).
+format:
+	stylua .
+
+# Local gate: formatting check. Luacheck runs in CI (.github/workflows/lint.yml).
+lint:
+	stylua --check .
+
+check: lint test
diff --git a/lua/md-render/content_builder.lua b/lua/md-render/content_builder.lua
index 538dae2..b00104f 100644
--- a/lua/md-render/content_builder.lua
+++ b/lua/md-render/content_builder.lua
@@ -185,7 +185,6 @@ end
 local wrap_mod = require "md-render.wrap"
 local icons = require "md-render.icons"
 
-local split_segments = wrap_mod.split_segments
 local wrap_words = wrap_mod.wrap_words
 
 --- Distribute markdown highlights across wrapped lines
@@ -1057,8 +1056,6 @@ function ContentBuilder:render_document(lines, opts)
   local callout_code_block_id = nil
   local callout_code_has_truncation = false
   local in_math_block = false
-  local math_block_start = nil
-  local math_block_id = nil
   local in_indented_code = false
   local in_comment_block = false
   local in_html_comment = false
@@ -1970,12 +1967,8 @@ function ContentBuilder:render_document(lines, opts)
     if not in_code_block and line:match "^%$%$$" then
       if not in_math_block then
         in_math_block = true
-        math_block_start = #self.lines
-        math_block_id = src_idx
       else
         in_math_block = false
-        math_block_start = nil
-        math_block_id = nil
       end
     elseif in_math_block then
       local indented = indent .. line
diff --git a/lua/md-render/display_utils.lua b/lua/md-render/display_utils.lua
index bb4f3b2..85e987a 100644
--- a/lua/md-render/display_utils.lua
+++ b/lua/md-render/display_utils.lua
@@ -1,4 +1,3 @@
-local FloatWin = require "md-render.float_win"
 local UrlHover = require "md-render.url_hover"
 
 local M = {}
@@ -480,8 +479,6 @@ function M.setup_images(win, content, ns, opts)
   -- across Neovim restarts but cleanup commands may not have been processed).
   image.clear_all()
 
-  local uv = vim.uv or vim.loop
-
   ---@type MdRender.ImageState
   local state = {
     placements = content.image_placements,
diff --git a/lua/md-render/image.lua b/lua/md-render/image.lua
index 00c61f6..fc67d4e 100644
--- a/lua/md-render/image.lua
+++ b/lua/md-render/image.lua
@@ -450,7 +450,7 @@ function M.render_mermaid(source)
   f:close()
 
   local cmd = build_mmdc_cmd(cmd_prefix, tmp_input, cache_path)
-  local result = vim.system(cmd, { text = true, timeout = 30000 }):wait()
+  vim.system(cmd, { text = true, timeout = 30000 }):wait()
   os.remove(tmp_input)
 
   if vim.fn.filereadable(cache_path) == 1 then return cache_path end
@@ -484,7 +484,7 @@ function M.render_mermaid_async(source, callback)
 
   local cmd = build_mmdc_cmd(cmd_prefix, tmp_input, cache_path)
 
-  vim.system(cmd, { text = true, timeout = 30000 }, function(result)
+  vim.system(cmd, { text = true, timeout = 30000 }, function(_)
     vim.schedule(function()
       os.remove(tmp_input)
       if vim.fn.filereadable(cache_path) == 1 then
@@ -514,6 +514,16 @@ end
 local _kitty_supported = nil
 local _is_ghostty = nil
 
+-- Mutable module state hoisted here so M.reset_cache() (defined below, before the
+-- sections that use these) resolves to the same upvalues. Declaring them only in
+-- the later sections left reset_cache() writing to accidental globals instead.
+local _convert_cmd = nil
+local _convert_checked = false
+local _anim_cmd = nil
+local _anim_checked = false
+local _image_id = 100
+local _session_cleared = false
+
 --- Check if running inside Ghostty terminal.
 --- Ghostty does not support t=t (temporary file transfer mode) in Kitty
 --- graphics protocol, so we must use t=f and clean up temp files ourselves.
@@ -915,9 +925,6 @@ end
 -- Image conversion tool detection
 -- ============================================================================
 
-local _convert_cmd = nil
-local _convert_checked = false
-
 --- Detect the best available tool for static image conversion (JPEG/WebP → PNG).
 --- Priority: sips (macOS) → ffmpeg → magick
 ---@return string? tool  "sips", "ffmpeg", or "magick"
@@ -934,9 +941,6 @@ local function find_convert_tool()
   return _convert_cmd
 end
 
-local _anim_cmd = nil
-local _anim_checked = false
-
 --- Detect the best available tool for animated GIF frame extraction.
 --- Priority: ffmpeg → magick
 ---@return string? tool  "ffmpeg" or "magick"
@@ -1156,10 +1160,8 @@ end
 -- Two-phase image display: transmit + put
 -- ============================================================================
 
-local _image_id = 100
 local _image_paths = {} -- image_id → file path (for Ghostty a=T workaround)
 local _temp_image_paths = {} -- image_id → true for temp files that need cleanup
-local _session_cleared = false
 
 --- Transmit image data to terminal (store without displaying).
 --- The image can then be displayed cheaply with put_image().
@@ -1263,6 +1265,12 @@ local function build_frame_extract_cmd(tool, path, cache_dir, total_frames)
   end
 end
 
+-- Forward declarations: these helpers are defined further down but are already
+-- referenced by M.transmit_animated below. Without this, the calls would resolve
+-- to (nil) globals instead of the locals.
+local get_frames_cache_dir
+local get_cached_frames
+
 --- Extract frames from an animated GIF and transmit each as a separate image.
 --- Large GIFs are resized and frames are sampled to stay under MAX_ANIM_FRAMES.
 --- Extracted frames are cached on disk for fast subsequent loads.
@@ -1365,7 +1373,7 @@ end
 --- Uses a hash of the source path to create a stable directory name.
 ---@param gif_path string
 ---@return string
-local function get_frames_cache_dir(gif_path)
+function get_frames_cache_dir(gif_path)
   local hash = vim.fn.sha256(gif_path):sub(1, 16)
   local dir = get_cache_dir() .. "/frames_" .. hash
   return dir
@@ -1375,7 +1383,7 @@ end
 ---@param gif_path string
 ---@param cache_dir string
 ---@return string[]?  sorted list of frame PNG paths, or nil if cache miss
-local function get_cached_frames(gif_path, cache_dir)
+function get_cached_frames(gif_path, cache_dir)
   local frames = vim.fn.glob(cache_dir .. "/frame_*.png", false, true)
   if #frames == 0 then return nil end
   table.sort(frames)
diff --git a/lua/md-render/markdown.lua b/lua/md-render/markdown.lua
index c3903e9..424a65e 100644
--- a/lua/md-render/markdown.lua
+++ b/lua/md-render/markdown.lua
@@ -513,42 +513,6 @@ local function process_underscore_emphasis(text, hl_group, highlights, links)
   return processed
 end
 
---- Process code markers (backticks) by removing them and adding highlights
----@param text string The input text
----@param hl_group string The highlight group to apply
----@param highlights MdRender.Markdown.Highlight[] Existing highlights to adjust
----@param links MdRender.Markdown.Link[] Existing links to adjust
----@return string processed The text with backticks removed
-local function process_code_markers(text, hl_group, highlights, links)
-  local pre_hl_count = #highlights
-  local pre_link_count = #links
-  local removals = {}
-  local processed = ""
-  local i = 1
-  while i <= #text do
-    if text:sub(i, i) == "`" then
-      local e = text:find("`", i + 1)
-      if e then
-        table.insert(removals, { start = i - 1, count = 1 })
-        table.insert(removals, { start = e - 1, count = 1 })
-        local content = text:sub(i + 1, e - 1)
-        local start_col = #processed
-        processed = processed .. content
-        table.insert(highlights, { col = start_col, end_col = start_col + #content, hl = hl_group })
-        i = e + 1
-      else
-        processed = processed .. text:sub(i, i)
-        i = i + 1
-      end
-    else
-      processed = processed .. text:sub(i, i)
-      i = i + 1
-    end
-  end
-  adjust_positions(highlights, links, removals, pre_hl_count, pre_link_count)
-  return processed
-end
-
 --- Process [[wikilinks]]: display as link text with highlight
 ---@param text string
 ---@param highlights MdRender.Markdown.Highlight[]
diff --git a/lua/md-render/markdown_table.lua b/lua/md-render/markdown_table.lua
index b8a740b..883547e 100644
--- a/lua/md-render/markdown_table.lua
+++ b/lua/md-render/markdown_table.lua
@@ -492,7 +492,6 @@ function MarkdownTable.render(parsed_table, indent, max_width, expanded, buf_dir
     for _, w in ipairs(col_widths) do
       content_sum = content_sum + w
     end
-    local total = overhead + content_sum
 
     if has_image_cells then
       -- Ensure columns are wide enough for actual image display sizes
@@ -517,7 +516,7 @@ function MarkdownTable.render(parsed_table, indent, max_width, expanded, buf_dir
     for _, w in ipairs(col_widths) do
       content_sum = content_sum + w
     end
-    total = overhead + content_sum
+    local total = overhead + content_sum
     if total > max_width then
       local budget = max_width - overhead
       if budget < num_cols then budget = num_cols end
@@ -583,7 +582,7 @@ function MarkdownTable.render(parsed_table, indent, max_width, expanded, buf_dir
       local display_text = cell.text
       local cell_hls = cell.highlights
       local cell_links = cell.links
-      local truncated_byte_len = #display_text
+      local truncated_byte_len
 
       -- Truncate cell text if it exceeds the (possibly shrunk) column width
       if vim.api.nvim_strwidth(display_text) > col_widths[col] then
diff --git a/lua/md-render/preview.lua b/lua/md-render/preview.lua
index fbc6508..17a0089 100644
--- a/lua/md-render/preview.lua
+++ b/lua/md-render/preview.lua
@@ -1030,7 +1030,6 @@ local function install_scroll_sync(session)
     -- small margin so a one-line move on the source side doesn't
     -- immediately push it off-screen on the render side.
     if target_cursor then
-      local cursor = math.max(1, math.floor(target_cursor + 0.5))
       local margin = math.min(3, math.floor(dest_height / 4))
       if cursor < topline + margin then
         topline = cursor - margin
diff --git a/lua/md-render/tty.lua b/lua/md-render/tty.lua
index 97a446f..4608f74 100644
--- a/lua/md-render/tty.lua
+++ b/lua/md-render/tty.lua
@@ -4,7 +4,6 @@
 --- module's public API returns nil without invoking any FFI calls.
 
 local ffi = require "ffi"
-local uv = vim.uv or vim.loop
 
 local M = {}
 
diff --git a/lua/md-render/wrap.lua b/lua/md-render/wrap.lua
index 1f407c8..85ace1b 100644
--- a/lua/md-render/wrap.lua
+++ b/lua/md-render/wrap.lua
@@ -717,7 +717,6 @@ function M.wrap_words(text, max_width)
 
   -- For kinsoku 追い出し: track state before the last segment was appended
   local prev_current = ""
-  local prev_width = 0
   local last_seg_text = ""
   local last_seg_pos = 0
 
@@ -786,7 +785,6 @@ function M.wrap_words(text, max_width)
         current_width = seg_width
       end
       prev_current = ""
-      prev_width = 0
       last_seg_text = ""
       last_seg_pos = 0
     else
@@ -804,7 +802,6 @@ function M.wrap_words(text, max_width)
           current_start = seg.byte_pos
           current_width = seg_width
           prev_current = ""
-          prev_width = 0
           last_seg_text = ""
           last_seg_pos = 0
           goto continue
@@ -813,7 +810,6 @@ function M.wrap_words(text, max_width)
 
       -- Save state before appending (for potential 追い出し on the next segment)
       prev_current = current
-      prev_width = current_width
       last_seg_text = seg.text
       last_seg_pos = seg.byte_pos