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 91a0ab2..636f4d0 100644
--- a/flake.nix
+++ b/flake.nix
@@ -19,9 +19,9 @@
     {
       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
@@ -33,7 +33,23 @@
             pkgs.selene
             pkgs.lua-language-server
           ];
-        };
-      });
+        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/init.lua b/lua/preview/init.lua
index 322b893..7cb982b 100644
--- a/lua/preview/init.lua
+++ b/lua/preview/init.lua
@@ -105,6 +105,12 @@ function M.setup(opts)
     vim.validate(prefix .. '.detach', provider.detach, 'boolean', true)
   end
 
+  if providers['plantuml'] then
+    vim.filetype.add({
+      extension = { puml = 'plantuml', pu = 'plantuml' },
+    })
+  end
+
   config = vim.tbl_deep_extend('force', default_config, {
     debug = debug,
     providers = providers,
diff --git a/lua/preview/presets.lua b/lua/preview/presets.lua
index 3591a21..1b5333e 100644
--- a/lua/preview/presets.lua
+++ b/lua/preview/presets.lua
@@ -271,6 +271,68 @@ M.asciidoctor = {
   reload = true,
 }
 
+---@type preview.ProviderConfig
+M.plantuml = {
+  ft = 'plantuml',
+  cmd = { 'plantuml' },
+  args = function(ctx)
+    return { '-tsvg', ctx.file }
+  end,
+  output = function(ctx)
+    return (ctx.file:gsub('%.puml$', '.svg'))
+  end,
+  error_parser = function(output)
+    local diagnostics = {}
+    for line in output:gmatch('[^\r\n]+') do
+      local lnum = line:match('^Error line (%d+) in file:')
+      if lnum then
+        table.insert(diagnostics, {
+          lnum = tonumber(lnum) - 1,
+          col = 0,
+          message = line,
+          severity = vim.diagnostic.severity.ERROR,
+        })
+      end
+    end
+    return diagnostics
+  end,
+  clean = function(ctx)
+    return { 'rm', '-f', (ctx.file:gsub('%.puml$', '.svg')) }
+  end,
+  open = true,
+}
+
+---@type preview.ProviderConfig
+M.mermaid = {
+  ft = 'mermaid',
+  cmd = { 'mmdc' },
+  args = function(ctx)
+    return { '-i', ctx.file, '-o', ctx.output }
+  end,
+  output = function(ctx)
+    return (ctx.file:gsub('%.mmd$', '.svg'))
+  end,
+  error_parser = function(output)
+    local diagnostics = {}
+    for line in output:gmatch('[^\r\n]+') do
+      local lnum = line:match('^%s*Parse error on line (%d+)')
+      if lnum then
+        table.insert(diagnostics, {
+          lnum = tonumber(lnum) - 1,
+          col = 0,
+          message = line,
+          severity = vim.diagnostic.severity.ERROR,
+        })
+      end
+    end
+    return diagnostics
+  end,
+  clean = function(ctx)
+    return { 'rm', '-f', (ctx.file:gsub('%.mmd$', '.svg')) }
+  end,
+  open = true,
+}
+
 ---@type preview.ProviderConfig
 M.quarto = {
   ft = 'quarto',