diff --git a/README.md b/README.md
index 3ffbc38..80a2650 100644
--- a/README.md
+++ b/README.md
@@ -11,7 +11,7 @@ Typst, Markdown, etc.)—diagnostics included.
 
 - Async compilation via `vim.system()`
 - Built-in presets for Typst, LaTeX (latexmk, pdflatex, tectonic), Markdown,
-  GitHub-flavored Markdown, AsciiDoc, and Quarto
+  GitHub-flavored Markdown, AsciiDoc, PlantUML, Mermaid, and Quarto
 - Compiler errors via `vim.diagnostic` or quickfix
 - Previewer auto-close on buffer deletion
 
diff --git a/doc/preview.txt b/doc/preview.txt
index 0e54a62..383a8f5 100644
--- a/doc/preview.txt
+++ b/doc/preview.txt
@@ -11,7 +11,7 @@ in Neovim. It provides a unified interface for any compilation workflow —
 LaTeX, Typst, Markdown, or anything else with a CLI compiler.
 
 The plugin ships with opt-in presets for common tools (Typst, LaTeX, Pandoc,
-AsciiDoc, Quarto) and supports fully custom providers.
+AsciiDoc, PlantUML, Mermaid, Quarto) and supports fully custom providers.
 See |preview-presets|.
 
 ==============================================================================
@@ -180,6 +180,8 @@ override individual fields by passing a table instead: >lua
   `markdown`           pandoc → HTML (standalone, embedded)
   `github`             pandoc → HTML (GitHub-styled, `-f gfm` input)
   `asciidoctor`        asciidoctor → HTML (AsciiDoc with SSE reload)
+  `plantuml`           plantuml → SVG (UML diagrams, `.puml`)
+  `mermaid`            mmdc → SVG (Mermaid diagrams, `.mmd`)
   `quarto`             quarto render → HTML (scientific publishing)
 
 ==============================================================================
diff --git a/flake.nix b/flake.nix
index d5bdae4..f6c279b 100644
--- a/flake.nix
+++ b/flake.nix
@@ -19,9 +19,10 @@
     {
       formatter = forEachSystem (pkgs: pkgs.nixfmt-tree);
 
-      devShells = forEachSystem (pkgs: {
-        default = pkgs.mkShell {
-          packages = [
+      devShells = forEachSystem (
+        pkgs:
+        let
+          devTools = [
             (pkgs.luajit.withPackages (
               ps: with ps; [
                 busted
@@ -32,10 +33,25 @@
             pkgs.stylua
             pkgs.selene
             pkgs.lua-language-server
-            pkgs.plantuml
-            pkgs.mermaid-cli
           ];
-        };
-      });
+        in
+        {
+          default = pkgs.mkShell {
+            packages = devTools;
+          };
+          presets = pkgs.mkShell {
+            packages = devTools ++ [
+              pkgs.typst
+              pkgs.texliveMedium
+              pkgs.tectonic
+              pkgs.pandoc
+              pkgs.asciidoctor
+              pkgs.quarto
+              pkgs.plantuml
+              pkgs.mermaid-cli
+            ];
+          };
+        }
+      );
     };
 }
diff --git a/lua/preview/presets.lua b/lua/preview/presets.lua
index 1b5333e..d4b03cc 100644
--- a/lua/preview/presets.lua
+++ b/lua/preview/presets.lua
@@ -115,6 +115,24 @@ local function parse_asciidoctor(output)
   return diagnostics
 end
 
+---@param output string
+---@return preview.Diagnostic[]
+local function parse_mermaid(output)
+  local lnum = output:match('Parse error on line (%d+)')
+  if not lnum then
+    return {}
+  end
+  local msg = output:match('(Expecting .+)') or 'parse error'
+  return {
+    {
+      lnum = tonumber(lnum) - 1,
+      col = 0,
+      message = msg,
+      severity = vim.diagnostic.severity.ERROR,
+    },
+  }
+end
+
 ---@type preview.ProviderConfig
 M.typst = {
   ft = 'typst',
@@ -313,19 +331,7 @@ M.mermaid = {
     return (ctx.file:gsub('%.mmd$', '.svg'))
   end,
   error_parser = function(output)
-    local diagnostics = {}
-    for line in output:gmatch('[^\r\n]+') do
-      local lnum = line:match('^%s*Parse error on line (%d+)')
-      if lnum then
-        table.insert(diagnostics, {
-          lnum = tonumber(lnum) - 1,
-          col = 0,
-          message = line,
-          severity = vim.diagnostic.severity.ERROR,
-        })
-      end
-    end
-    return diagnostics
+    return parse_mermaid(output)
   end,
   clean = function(ctx)
     return { 'rm', '-f', (ctx.file:gsub('%.mmd$', '.svg')) }