diff --git a/README.md b/README.md
index b42ddac..c9a8804 100644
--- a/README.md
+++ b/README.md
@@ -18,7 +18,16 @@ To display only selected chains (supports regexp):
 
 To also render empty chains:
 
-`awk -f iptables-vis.awk -v 'include_empty_chains=1 < iptables.txt > iptables.dia'`
+`awk -f iptables-vis.awk -v 'include_empty_chains=1' < iptables.txt > iptables.dia`
+
+Mermaid Output
+===============
+Same as above, but use `iptables-vis-mermaid.awk`, e.g.
+
+`awk -f iptables-vis-mermaid.awk -v 'include_empty_chains=1' < iptables.txt > iptables.mmd`
+
+To `mermaid.html` file can be used to view mermaid files in the browser.
+It needs to be servied via HTTPS so it can load the mermaid failes.
 
 Legend
 ======
diff --git a/iptables-vis-mermaid.awk b/iptables-vis-mermaid.awk
new file mode 100755
index 0000000..d97c58c
--- /dev/null
+++ b/iptables-vis-mermaid.awk
@@ -0,0 +1,253 @@
+#!/usr/bin/awk -f
+#
+BEGIN {
+    print "flowchart TD"
+    counter = 0
+    edge_counter = 0
+}
+
+function make_id(s) {
+    gsub(/-/, "_", s)
+    return s
+}
+
+function sanitize_label(s) {
+    gsub(/"/, "'", s)
+    gsub(/  +/, " ", s)
+    gsub(/^ | $/, "", s)
+    return s
+}
+
+# Begin of a chain
+/^Chain/ {
+    chainname = $2
+    in_chain=1
+    is_a_chain[chainname] = 1
+    if ( chainname !~ chain_selector && chain_selector != "")
+        next
+    in_relevant_chain=1
+    if ( $3 == "(policy" )
+        policy=$4
+    else
+        policy=0
+    last=chainname
+    delete chain_buffer; chain_buf_size = 0
+    delete pending_edge_styles; chain_edge_counter = 0
+    delete filter_nodes; delete targets; delete target_node_names; delete target_labels
+    num_targets = 0
+    chain_buffer[chain_buf_size++] = "  subgraph sg_" make_id(chainname) " [\"" chainname "\"]"
+    chain_buffer[chain_buf_size++] = "    direction TB"
+}
+
+# Filter in chain
+in_chain && /^ *[0-9]/ {
+    filters_in_chain++
+    if ( !in_relevant_chain )
+        next
+    name="Node" counter++
+    reject_with=""
+    label=""
+    if ( $4 != "all" )
+        label=label $4 " "
+    if ( $5 != "--" )
+        label=label $5 " "
+    if ( $6 != "any" )
+        label=label "in:" $6 " "
+    if ( $7 != "any" )
+        label=label "out:" $7 " "
+    if ( $8 != "anywhere" )
+        label=label "src:" $8 " "
+    if ( $9 != "anywhere" )
+        label=label "dst:" $9 " "
+    comment=0
+    for (i=10; i<=NF; i++) {
+        if ( $i == "/*" )
+            comment=1
+        else if ( $i == "*/" )
+            comment=0
+        else if ( $i == "reject-with" ) {
+            i++
+            reject_with = $i
+            i++
+        }
+        else if ( ! comment )
+            label=label " " $i
+    }
+    if ( label == "" )
+        label = "*"
+    label = sanitize_label(label)
+    chain_buffer[chain_buf_size++] = "    " name "{\"" label "\"}:::rule"
+    chain_buffer[chain_buf_size++] = "    " make_id(last) " --> " name
+    chain_edge_counter++
+    last=name
+    filter_nodes[num_targets++] = name
+    target_node_name = chainname "_" $3
+    if ( reject_with )
+        target_node_name = target_node_name "_" reject_with
+    target_label = $3
+    if ( reject_with )
+        target_label = target_label "<br/>" reject_with
+
+    targets[name] = $3
+    all_targets[name] = $3
+    target_node_names[name] = target_node_name
+    all_target_node_names[name] = target_node_name
+    target_labels[target_node_name] = target_label
+}
+
+# End of chain
+/^$/ {
+    in_chain=0
+    filter_number[chainname] = filters_in_chain
+    if (in_relevant_chain)
+        finalize_chain()
+    filters_in_chain=0
+    in_relevant_chain=0
+}
+
+function finalize_chain(    i, head_class, pol_target_node, pol_target_id, idx, name, target, target_node_name, target_label, target_id, rhs, safe_lbl) {
+    if ( !filters_in_chain && !include_empty_chains ) {
+        delete chain_buffer; chain_buf_size = 0
+        delete pending_edge_styles; chain_edge_counter = 0
+        delete filter_nodes; delete targets
+        delete target_node_names; delete target_labels
+        num_targets = 0
+        return
+    }
+
+    # Determine chain head class
+    if ( !filters_in_chain )
+        head_class = ":::chain_empty"
+    else if ( chainname ~ "^(INPUT|OUTPUT|FORWARD|PREROUTING|POSTROUTING)$" )
+        head_class = ":::chain_head_builtin"
+    else
+        head_class = ":::chain_head"
+
+    # Track chain order for top-alignment links emitted in END
+    chain_order[num_chains++] = make_id(chainname)
+
+    # Chain head node definition (inside subgraph)
+    chain_buffer[chain_buf_size++] = "    " make_id(chainname) "[\"" chainname "\"]" head_class
+
+    # Policy edge + target node (inside subgraph)
+    if ( policy ) {
+        pol_target_node = chainname "_" policy
+        pol_target_id = make_id(pol_target_node)
+        chain_buffer[chain_buf_size++] = "    " make_id(last) " --> " pol_target_id
+        if ( policy ~ "^ACCEPT$" )
+            pending_edge_styles[chain_edge_counter] = "stroke:green"
+        else if ( policy ~ "^(DROP|REJECT)" )
+            pending_edge_styles[chain_edge_counter] = "stroke:red"
+        chain_edge_counter++
+        if ( !already_rendered[pol_target_node] ) {
+            already_rendered[pol_target_node] = 1
+            if ( policy ~ "^ACCEPT$" )
+                chain_buffer[chain_buf_size++] = "    " pol_target_id "[\"ACCEPT\"]:::accept"
+            else if ( policy ~ "^DROP$" )
+                chain_buffer[chain_buf_size++] = "    " pol_target_id "[\"DROP\"]:::drop"
+            else if ( policy ~ "^REJECT($|_)" )
+                chain_buffer[chain_buf_size++] = "    " pol_target_id "[\"REJECT\"]:::reject"
+            else if ( policy ~ "^RETURN$" )
+                chain_buffer[chain_buf_size++] = "    " pol_target_id "[\"RETURN\"]:::return"
+        }
+    }
+
+    # Rule-to-target edges + target node definitions (all inside subgraph)
+    for ( idx = 0; idx < num_targets; idx++ ) {
+        name = filter_nodes[idx]
+        target = targets[name]
+        target_node_name = target_node_names[name]
+        target_label = target_labels[target_node_name]
+        target_id = make_id(target_node_name)
+
+        if ( target ~ "^ACCEPT$" )
+            pending_edge_styles[chain_edge_counter] = "stroke:green"
+        else if ( target ~ "^REJECT($|_)|DROP$" )
+            pending_edge_styles[chain_edge_counter] = "stroke:red"
+        else if ( target ~ "^RETURN$" )
+            pending_edge_styles[chain_edge_counter] = "stroke:blue"
+
+        if ( !already_rendered[target_node_name] ) {
+            already_rendered[target_node_name] = 1
+            if ( target ~ "^ACCEPT$" )
+                rhs = target_id "[\"ACCEPT\"]:::accept"
+            else if ( target ~ "^DROP$" )
+                rhs = target_id "[\"DROP\"]:::drop"
+            else if ( target ~ "^REJECT($|_)" ) {
+                safe_lbl = sanitize_label(target_label)
+                rhs = target_id "[\"" safe_lbl "\"]:::reject"
+            }
+            else if ( target ~ "^RETURN$" )
+                rhs = target_id "[\"RETURN\"]:::return"
+            else {
+                safe_lbl = sanitize_label(target_label)
+                rhs = target_id "[\"" safe_lbl "\"]:::chain_target"
+            }
+        } else {
+            rhs = target_id
+        }
+
+        chain_buffer[chain_buf_size++] = "    " name " --> " rhs
+        chain_edge_counter++
+    }
+
+    # Close subgraph
+    chain_buffer[chain_buf_size++] = "  end"
+
+    # Merge pending edge styles into global edge_styles at current offset
+    for ( i = 0; i < chain_edge_counter; i++ ) {
+        if ( i in pending_edge_styles )
+            edge_styles[edge_counter + i] = pending_edge_styles[i]
+    }
+
+    # Flush chain buffer
+    for ( i = 0; i < chain_buf_size; i++ )
+        print chain_buffer[i]
+    edge_counter += chain_edge_counter
+
+    delete chain_buffer; chain_buf_size = 0
+    delete pending_edge_styles; chain_edge_counter = 0
+    delete filter_nodes; delete targets
+    delete target_node_names; delete target_labels
+    num_targets = 0
+    # Note: do NOT delete already_rendered — it is global across chains
+}
+
+END {
+    filter_number[chainname] = filters_in_chain
+    if (in_relevant_chain)
+        finalize_chain()
+
+    # Override style for custom chain targets that turned out to be empty chains
+    for ( name in all_targets ) {
+        target = all_targets[name]
+        if ( !is_a_chain[target] )
+            continue
+        target_node_name = all_target_node_names[name]
+        if ( filter_number[target] == 0 && !style_overridden[target_node_name] ) {
+            style_overridden[target_node_name] = 1
+            print "  style " make_id(target_node_name) " fill:#eeeeee,stroke:#aaaaaa,stroke-dasharray:5 5"
+        }
+    }
+
+    # linkStyle directives for colored edges
+    for ( i = 0; i < edge_counter; i++ ) {
+        if ( i in edge_styles )
+            print "  linkStyle " i " " edge_styles[i]
+    }
+
+    # Invisible links from the first chain head to all others to force top-alignment
+    for ( i = 1; i < num_chains; i++ )
+        print "  " chain_order[0] " ~~~ " chain_order[i]
+
+    # classDef declarations
+    print "  classDef accept fill:lightgreen,stroke:green"
+    print "  classDef drop fill:#ff6666,stroke:red"
+    print "  classDef reject fill:#ff9999,stroke:red"
+    print "  classDef return fill:#1ab3ff,stroke:blue"
+    print "  classDef rule fill:white,stroke:black"
+    print "  classDef chain_head fill:white,stroke:black"
+    print "  classDef chain_head_builtin fill:#ffffcc,stroke:#999900"
+    print "  classDef chain_target fill:white,stroke:#666"
+    print "  classDef chain_empty fill:#eeeeee,stroke:#aaaaaa,stroke-dasharray:5 5"
+}
diff --git a/mermaid.html b/mermaid.html
new file mode 100644
index 0000000..08686f5
--- /dev/null
+++ b/mermaid.html
@@ -0,0 +1,151 @@
+<!-- This file was generated/modified by GitHub Copilot. -->
+<!doctype html>
+<html lang="en">
+
+<head>
+    <meta charset="utf-8" />
+    <meta name="viewport" content="width=device-width, initial-scale=1" />
+    <title>Mermaid Viewer</title>
+    <style>
+        body {
+            font-family: system-ui, sans-serif;
+            margin: 16px;
+        }
+
+        #toolbar {
+            display: flex;
+            gap: 8px;
+            align-items: center;
+            flex-wrap: wrap;
+        }
+
+        #source {
+            width: 520px;
+            max-width: 100%;
+            height: 7em;
+            font-family: ui-monospace, monospace;
+        }
+
+        #diagram {
+            border: 1px solid #ddd;
+            padding: 12px;
+            margin-top: 12px;
+            overflow: auto;
+        }
+
+        .hint {
+            color: #555;
+            font-size: 0.95em;
+        }
+    </style>
+
+    <script type="module">
+        import mermaid from "https://cdn.jsdelivr.net/npm/mermaid@11/dist/mermaid.esm.min.mjs";
+
+        mermaid.initialize({
+            startOnLoad: false,
+            securityLevel: "loose",
+            theme: "default"
+        });
+
+        let lastSvgText = null;
+
+        function downloadBlob(filename, blob) {
+            const url = URL.createObjectURL(blob);
+            const a = document.createElement("a");
+            a.href = url;
+            a.download = filename;
+            document.body.appendChild(a);
+            a.click();
+            a.remove();
+            URL.revokeObjectURL(url);
+        }
+
+        function downloadText(filename, text, mime) {
+            downloadBlob(filename, new Blob([text], {type: mime}));
+        }
+
+        async function renderToSvg(text) {
+            const id = "mmd-" + crypto.randomUUID();
+            const {svg} = await mermaid.render(id, text);
+            lastSvgText = svg;
+            document.getElementById("diagram").innerHTML = svg;
+        }
+
+        async function loadAndRender(filename) {
+            const res = await fetch(filename, {cache: "no-store"});
+            if (!res.ok) throw new Error(`Fetch failed: ${res.status} ${res.statusText}`);
+            const text = await res.text();
+            document.getElementById("source").value = text;
+            await renderToSvg(text);
+            history.replaceState(null, "", `?file=${encodeURIComponent(filename)}`);
+
+            document.getElementById("downloadSvgName").value =
+                filename.replace(/\.[^.]+$/, "") + ".svg";
+        }
+
+        function getQueryFile() {
+            const p = new URLSearchParams(location.search);
+            return p.get("file");
+        }
+
+        window.addEventListener("DOMContentLoaded", async () => {
+            const fileInput = document.getElementById("file");
+            const loadBtn = document.getElementById("load");
+            const renderBtn = document.getElementById("render");
+
+            const dlSvgBtn = document.getElementById("downloadSvg");
+
+            loadBtn.addEventListener("click", async () => {
+                try {await loadAndRender(fileInput.value.trim());}
+                catch (e) {alert(e.message);}
+            });
+
+            renderBtn.addEventListener("click", async () => {
+                try {await renderToSvg(document.getElementById("source").value);}
+                catch (e) {alert(e.message);}
+            });
+
+            dlSvgBtn.addEventListener("click", () => {
+                if (!lastSvgText) return alert("Nothing rendered yet.");
+                const name = (document.getElementById("downloadSvgName").value || "diagram.svg").trim();
+                downloadText(name, lastSvgText, "image/svg+xml;charset=utf-8");
+            });
+
+            const qf = getQueryFile();
+            if (qf) {
+                fileInput.value = qf;
+                try {await loadAndRender(qf);} catch { }
+            }
+        });
+    </script>
+</head>
+
+<body>
+    <p class="hint">
+        A very basic viewer for Mermaid files, generated by Copilot.
+    </p>
+
+    <p class="hint">
+        Serve this file over http(s) for this to work, use something like
+        <br />
+        <code>python3 -m http.server 8000</code> or <code>npx -y serve .</code> or <code>php -S 8000</code>
+    </p>
+
+    <div id="toolbar">
+        <label>File:</label>
+        <input id="file" value="diagram.mmd" />
+        <button id="load">Load .mmd</button>
+        <button id="render">Render textarea</button>
+
+        <span style="margin-left: 12px;"></span>
+
+        <input hidden id="downloadSvgName" value="diagram.svg" />
+        <button id="downloadSvg">Download SVG</button>
+    </div>
+
+    <textarea id="source" spellcheck="false"></textarea>
+    <div id="diagram"></div>
+</body>
+
+</html>