diff --git a/Makefile b/Makefile
index a7433a3..0c96af8 100644
--- a/Makefile
+++ b/Makefile
@@ -1,55 +1,54 @@
-pandocrepo = https://github.com/kdheepak/panvimdoc
-pandocdir = misc/panvimdoc
-TEST_DIR = test/github-theme
-PLENARY_DIR = test/plenary
-PLENARY_URL = https://github.com/nvim-lua/plenary.nvim/
+pandocrepo  ::= https://github.com/kdheepak/panvimdoc
+pandocdir   ::= misc/panvimdoc
+TEST_DIR    ::= test/github-theme
+PLENARY_DIR ::= test/plenary
+PLENARY_URL ::= https://github.com/nvim-lua/plenary.nvim/
 
-root_dir := $(shell dirname $(realpath $(firstword $(MAKEFILE_LIST))))
+root_dir    ::= $(shell dirname $(realpath $(firstword $(MAKEFILE_LIST))))
 
-.PHONY : all
+.PHONY: all docgen test check fmt diagnose
 all: docgen test check
 
-.PHONY : docgen
 docgen: $(pandocdir)
-		@pandoc \
-		--citeproc \
-		--shift-heading-level-by=0 \
-		--metadata=project:github-nvim-theme \
-		--metadata=vimversion:8.0 \
-		--metadata=toc:true \
-		--metadata="description:Github's Neovim themes" \
-		--metadata=dedupsubheadings:true \
-		--metadata=ignorerawblocks:true \
-		--metadata=docmapping:true \
-		--metadata=docmappingproject:true \
-		--metadata=treesitter:true \
-		--metadata=incrementheadinglevelby:0 \
-		--lua-filter=misc/panvimdoc/scripts/skip-blocks.lua \
-		--lua-filter=misc/panvimdoc/scripts/include-files.lua \
-		-t misc/panvimdoc/scripts/panvimdoc.lua \
-		-o doc/github-nvim-theme.txt \
-		Usage.md
+	@pandoc \
+	    --citeproc \
+	    --shift-heading-level-by=0 \
+	    --metadata=project:github-nvim-theme \
+	    --metadata=vimversion:8.0 \
+	    --metadata=toc:true \
+	    --metadata="description:Github's Neovim themes" \
+	    --metadata=dedupsubheadings:true \
+	    --metadata=ignorerawblocks:true \
+	    --metadata=docmapping:true \
+	    --metadata=docmappingproject:true \
+	    --metadata=treesitter:true \
+	    --metadata=incrementheadinglevelby:0 \
+	    --lua-filter=misc/panvimdoc/scripts/skip-blocks.lua \
+	    --lua-filter=misc/panvimdoc/scripts/include-files.lua \
+	    -t misc/panvimdoc/scripts/panvimdoc.lua \bu
+	    -o doc/github-nvim-theme.txt \
+	    Usage.md
 
 $(pandocdir):
 	git clone --depth=1 --no-single-branch $(pandocrepo) $(pandocdir)
 	@rm -rf doc/panvimdoc/.git
 
-.PHONY : test
 test: $(PLENARY_DIR)
 	nvim \
-		--headless \
-		--noplugin \
-		-u test/minimal_init.vim \
-		-c "PlenaryBustedDirectory $(TEST_DIR) { minimal_init = './test/minimal_init.vim', sequential = true }"
+	    --headless \
+	    --noplugin \
+	    -u test/minimal_init.vim \
+	    -c "PlenaryBustedDirectory $(TEST_DIR) { minimal_init = './test/minimal_init.vim', sequential = true }"
 
 $(PLENARY_DIR):
 	git clone --depth=1 --no-single-branch $(PLENARY_URL) $(PLENARY_DIR)
 	@rm -rf $(PLENARY_DIR)/.git
 
-.PHONY : check
-check :
+check:
 	stylua --check lua/ test -f ./stylua.toml
 
-.PHONY : fmt
-fmt :
+fmt:
 	stylua lua/ test/ -f ./stylua.toml
+
+diagnose:
+	scripts/diagnose Hint
diff --git a/scripts/diagnose b/scripts/diagnose
new file mode 100755
index 0000000..05199b3
--- /dev/null
+++ b/scripts/diagnose
@@ -0,0 +1,44 @@
+#!/usr/bin/env bash
+
+set -eu
+
+# One of: Error, Warning, Information, or Hint
+level="$1"
+
+export VIMRUNTIME="${VIMRUNTIME-"$(nvim -i NONE -es <<<'lua io.write(vim.env.VIMRUNTIME)')"}"
+export LUA_LS="${LUA_LS-"$(which lua-language-server)"}"
+
+# Add vim's stdlib to library files, and never diagnose lib files (since ALL
+# files will be `Opened` by the lsp to do the check).
+extcfg='
+{
+  workspace: {
+    library: [ $ENV.VIMRUNTIME, .workspace.library[] ]
+  },
+  diagnostics: { ignoredFiles: "Disable", libraryFiles: "Disable" }
+}
+'
+
+jq='
+  to_entries[]
+    | (.key | ltrimstr("file://") | ltrimstr($ENV.PWD)) as $f
+    | .value[]
+      | . as {range: {start: {line: $l, character: $c}, end: {line: $eL, character: $eC}}}
+      | [null, "error", "warning", "notice", "notice"][.severity] as $s
+      | "::\($s) file=\($f),line=\($l),col=\($c),endLine=\($eL),endColumn=\($eC),title=\(.code)::\(.message)"
+'
+
+"$LUA_LS" \
+    --check="$PWD" \
+    --checklevel="$level" \
+    --logpath=.log \
+    --metapath=.meta \
+    --configpath=<(jq ". * $extcfg" .luarc.json)
+
+if [ "${CI-no}" = no ]; then
+    jq -r 'to_entries[] | "\(.key):\(.value[] | "\(.range.start.line): \(.message)")", ""' .log/check.json
+else
+    jq -r "$jq" .log/check.json
+fi
+
+[ "$(jq 'isempty(.[]?)' .log/check.json)" = true ] || exit 1