diff --git a/profiles/aom.js b/profiles/aom.js
index db075aa1d6..fa17e2fb5c 100644
--- a/profiles/aom.js
+++ b/profiles/aom.js
@@ -42,6 +42,7 @@ const modules = [
   import("../src/core/highlight-vars.js"),
   import("../src/core/data-type.js"),
   import("../src/core/anchor-expander.js"),
+  import("../src/core/grammar-boxes.js"),
   import("../src/core/dfn-panel.js"),
   import("../src/core/custom-elements/index.js"),
   import("../src/core/dfn-contract.js"),
diff --git a/profiles/dini.js b/profiles/dini.js
index 0315e6d46e..9f6e6649fb 100644
--- a/profiles/dini.js
+++ b/profiles/dini.js
@@ -42,6 +42,7 @@ const modules = [
   import("../src/core/highlight-vars.js"),
   import("../src/core/data-type.js"),
   import("../src/core/anchor-expander.js"),
+  import("../src/core/grammar-boxes.js"),
   import("../src/core/dfn-panel.js"),
   import("../src/core/custom-elements/index.js"),
   import("../src/core/dfn-contract.js"),
diff --git a/profiles/geonovum.js b/profiles/geonovum.js
index 798a323b35..238e9a7d4d 100644
--- a/profiles/geonovum.js
+++ b/profiles/geonovum.js
@@ -41,6 +41,7 @@ const modules = [
   import("../src/core/list-sorter.js"),
   import("../src/core/highlight-vars.js"),
   import("../src/core/anchor-expander.js"),
+  import("../src/core/grammar-boxes.js"),
   import("../src/core/dfn-panel.js"),
   import("../src/core/dfn-contract.js"),
   /* Linter must be the last thing to run */
diff --git a/profiles/w3c.js b/profiles/w3c.js
index cdf270af71..ee8e8c3588 100644
--- a/profiles/w3c.js
+++ b/profiles/w3c.js
@@ -30,6 +30,7 @@ const modules = [
   import("../src/core/tables.js"),
   import("../src/core/webidl.js"),
   import("../src/core/cddl.js"),
+  import("../src/core/grammar-boxes.js"),
   import("../src/core/biblio.js"),
   import("../src/core/link-to-dfn.js"),
   import("../src/core/xref.js"),
diff --git a/src/core/grammar-boxes.js b/src/core/grammar-boxes.js
new file mode 100644
index 0000000000..02f6eca900
--- /dev/null
+++ b/src/core/grammar-boxes.js
@@ -0,0 +1,77 @@
+// @ts-check
+import { createCopyButton, injectCopyScript } from "./clipboard.js";
+import { addHashId } from "./utils.js";
+import css from "../styles/grammar.css.js";
+
+export const name = "core/grammar-boxes";
+
+/** @type {ReadonlyMap<string, string>} */
+const GRAMMARS = new Map([
+  ["abnf", "ABNF"],
+  ["ebnf", "EBNF"],
+  ["bnf", "BNF"],
+]);
+
+/**
+ * Add a header badge and copy button to a single grammar pre block.
+ * Wraps the block content in a <code> element (matching WebIDL/CDDL pattern)
+ * so that core/highlight can pick it up via the `pre > code` selector.
+ *
+ * @param {HTMLPreElement} pre
+ * @param {string} label - display label, e.g. "ABNF"
+ * @param {string} lang - grammar class name, e.g. "abnf"
+ */
+function processGrammarBlock(pre, label, lang) {
+  addHashId(pre, `${lang}-block`);
+
+  const code = document.createElement("code");
+  code.className = lang;
+  code.textContent = pre.textContent;
+  pre.textContent = "";
+  pre.append(code);
+  pre.classList.add("def", "highlight");
+
+  const header = document.createElement("span");
+  header.className = "grammarHeader";
+  const selfLink = document.createElement("a");
+  selfLink.className = "self-link";
+  selfLink.href = `#${pre.id}`;
+  selfLink.textContent = label;
+  header.append(selfLink);
+
+  const copyButton = createCopyButton(".grammarHeader");
+  header.append(copyButton);
+
+  pre.prepend(header);
+}
+
+export async function run() {
+  /** @type {Array<{pre: HTMLPreElement, label: string, lang: string}>} */
+  const blocks = [];
+  GRAMMARS.forEach((label, lang) => {
+    document
+      .querySelectorAll(`pre.${lang}:not([data-no-grammar])`)
+      .forEach(pre => {
+        blocks.push({ pre: /** @type {HTMLPreElement} */ (pre), label, lang });
+      });
+  });
+
+  if (!blocks.length) return;
+
+  // Inject CSS once.
+  const style = document.createElement("style");
+  style.textContent = css;
+  const anchor = document.querySelector("head link, head > *:last-child");
+  if (anchor) {
+    anchor.before(style);
+  } else {
+    document.head.append(style);
+  }
+
+  blocks.forEach(({ pre, label, lang }) =>
+    processGrammarBlock(pre, label, lang)
+  );
+
+  // Inject the runtime copy-paste script (survives document export).
+  injectCopyScript();
+}
diff --git a/src/styles/grammar.css.js b/src/styles/grammar.css.js
new file mode 100644
index 0000000000..c16b1aa18d
--- /dev/null
+++ b/src/styles/grammar.css.js
@@ -0,0 +1,56 @@
+const css = String.raw;
+
+// prettier-ignore
+export default css`
+:root {
+  --grammar-header-bg: var(--def-border, #8ccbf2);
+  --grammar-header-color: #005a9c;
+  --grammar-focus: #51a7e8;
+}
+
+@media (prefers-color-scheme: dark) {
+  :root {
+    --grammar-header-bg: #3a6da0;
+    --grammar-header-color: #fff;
+  }
+}
+
+pre:is(.abnf, .ebnf, .bnf) {
+  padding: 1em;
+  position: relative;
+}
+
+pre:is(.abnf, .ebnf, .bnf) > code {
+  color: var(--text, black);
+}
+
+@media print {
+  pre:is(.abnf, .ebnf, .bnf) {
+    white-space: pre-wrap;
+  }
+}
+
+.grammarHeader {
+  display: block;
+  width: 150px;
+  background: var(--grammar-header-bg);
+  color: var(--grammar-header-color);
+  font-family: sans-serif;
+  font-weight: bold;
+  margin: -1em 0 1em -1em;
+  height: 1.75em;
+  line-height: 1.75em;
+}
+
+.grammarHeader a.self-link {
+  margin-left: 0.5em;
+  text-decoration: none;
+  border-bottom: none;
+  color: inherit;
+}
+
+.grammarHeader a:focus-visible {
+  outline: 2px solid var(--grammar-focus);
+  outline-offset: 2px;
+}
+`;
diff --git a/tests/spec/core/grammar-boxes-spec.js b/tests/spec/core/grammar-boxes-spec.js
new file mode 100644
index 0000000000..34c3d42a7a
--- /dev/null
+++ b/tests/spec/core/grammar-boxes-spec.js
@@ -0,0 +1,193 @@
+"use strict";
+
+import { flushIframes, makeRSDoc, makeStandardOps } from "../SpecHelper.js";
+
+describe("Core — Grammar Boxes", () => {
+  afterAll(flushIframes);
+
+  describe("ABNF blocks", () => {
+    it("wraps ABNF content in a <code> element", async () => {
+      const body = `
+        <pre class="abnf">
+          rulename = "value"
+        </pre>
+      `;
+      const ops = makeStandardOps(null, body);
+      const doc = await makeRSDoc(ops);
+      const code = doc.querySelector("pre.abnf > code");
+      expect(code).toBeTruthy();
+      expect(code.textContent).toContain("rulename");
+    });
+
+    it("adds an ABNF header badge", async () => {
+      const body = `
+        <pre class="abnf">
+          rulename = "value"
+        </pre>
+      `;
+      const ops = makeStandardOps(null, body);
+      const doc = await makeRSDoc(ops);
+      const header = doc.querySelector("pre.abnf .grammarHeader");
+      expect(header).toBeTruthy();
+      const link = header.querySelector("a.self-link");
+      expect(link).toBeTruthy();
+      expect(link.textContent).toBe("ABNF");
+    });
+
+    it("adds an id to the pre element for self-linking", async () => {
+      const body = `
+        <pre class="abnf">
+          rulename = "value"
+        </pre>
+      `;
+      const ops = makeStandardOps(null, body);
+      const doc = await makeRSDoc(ops);
+      const pre = doc.querySelector("pre.abnf");
+      expect(pre.id).toBeTruthy();
+      expect(pre.id).toMatch(/^abnf-block-/);
+    });
+
+    it("self-link href matches the pre element id", async () => {
+      const body = `
+        <pre class="abnf">
+          rulename = "value"
+        </pre>
+      `;
+      const ops = makeStandardOps(null, body);
+      const doc = await makeRSDoc(ops);
+      const pre = doc.querySelector("pre.abnf");
+      const link = doc.querySelector("pre.abnf .grammarHeader a.self-link");
+      expect(link.getAttribute("href")).toBe(`#${pre.id}`);
+    });
+
+    it("skips blocks with data-no-grammar attribute", async () => {
+      const body = `
+        <pre id="skipped-abnf" class="abnf" data-no-grammar>
+          rulename = "value"
+        </pre>
+      `;
+      const ops = makeStandardOps(null, body);
+      const doc = await makeRSDoc(ops);
+      const pre = doc.getElementById("skipped-abnf");
+      expect(pre).toBeTruthy();
+      // grammar-boxes must not have added a header badge
+      expect(pre.querySelector(".grammarHeader")).toBeNull();
+      // grammar-boxes must not have added its own <code class="abnf"> (no hljs class)
+      const code = pre.querySelector("code");
+      if (code) {
+        // If highlight.js ran, the code element has the "hljs" class
+        expect(code.classList.contains("hljs")).toBe(true);
+      }
+    });
+
+    it("adds a copy button inside the header", async () => {
+      const body = `
+        <pre class="abnf">
+          rulename = "value"
+        </pre>
+      `;
+      const ops = makeStandardOps(null, body);
+      const doc = await makeRSDoc(ops);
+      const header = doc.querySelector("pre.abnf .grammarHeader");
+      const copyButton = header.querySelector(
+        "button.respec-button-copy-paste"
+      );
+      expect(copyButton).toBeTruthy();
+    });
+  });
+
+  describe("EBNF blocks", () => {
+    it("wraps EBNF content in a <code> element", async () => {
+      const body = `
+        <pre class="ebnf">
+          rule = "token" , rule
+        </pre>
+      `;
+      const ops = makeStandardOps(null, body);
+      const doc = await makeRSDoc(ops);
+      const code = doc.querySelector("pre.ebnf > code");
+      expect(code).toBeTruthy();
+      expect(code.textContent).toContain("rule");
+    });
+
+    it("adds an EBNF header badge", async () => {
+      const body = `
+        <pre class="ebnf">
+          rule = "token" , rule
+        </pre>
+      `;
+      const ops = makeStandardOps(null, body);
+      const doc = await makeRSDoc(ops);
+      const link = doc.querySelector("pre.ebnf .grammarHeader a.self-link");
+      expect(link).toBeTruthy();
+      expect(link.textContent).toBe("EBNF");
+    });
+  });
+
+  describe("BNF blocks", () => {
+    it("wraps BNF content in a <code> element", async () => {
+      const body = `
+        <pre class="bnf">
+          &lt;term&gt; ::= "value"
+        </pre>
+      `;
+      const ops = makeStandardOps(null, body);
+      const doc = await makeRSDoc(ops);
+      const code = doc.querySelector("pre.bnf > code");
+      expect(code).toBeTruthy();
+    });
+
+    it("adds a BNF header badge", async () => {
+      const body = `
+        <pre class="bnf">
+          &lt;term&gt; ::= "value"
+        </pre>
+      `;
+      const ops = makeStandardOps(null, body);
+      const doc = await makeRSDoc(ops);
+      const link = doc.querySelector("pre.bnf .grammarHeader a.self-link");
+      expect(link).toBeTruthy();
+      expect(link.textContent).toBe("BNF");
+    });
+  });
+
+  describe("CSS injection", () => {
+    it("injects grammar CSS when at least one grammar block exists", async () => {
+      const body = `
+        <pre class="abnf">
+          rulename = "value"
+        </pre>
+      `;
+      const ops = makeStandardOps(null, body);
+      const doc = await makeRSDoc(ops);
+      // The CSS must define .grammarHeader — check via computed style or
+      // inspect that the style element was injected.
+      const styles = [...doc.querySelectorAll("style")].map(s => s.textContent);
+      const hasGrammarCSS = styles.some(s => s.includes("grammarHeader"));
+      expect(hasGrammarCSS).toBe(true);
+    });
+
+    it("does not inject CSS when no grammar blocks are present", async () => {
+      const body = `<p>No grammar blocks here.</p>`;
+      const ops = makeStandardOps(null, body);
+      const doc = await makeRSDoc(ops);
+      const styles = [...doc.querySelectorAll("style")].map(s => s.textContent);
+      const hasGrammarCSS = styles.some(s => s.includes("grammarHeader"));
+      expect(hasGrammarCSS).toBe(false);
+    });
+  });
+
+  describe("<code> element language class", () => {
+    it("puts the grammar language class on the <code> element", async () => {
+      const body = `
+        <pre class="abnf">
+          rulename = "value"
+        </pre>
+      `;
+      const ops = makeStandardOps(null, body);
+      const doc = await makeRSDoc(ops);
+      const code = doc.querySelector("pre.abnf > code");
+      expect(code.classList.contains("abnf")).toBe(true);
+    });
+  });
+});
diff --git a/worker/respec-highlight.js b/worker/respec-highlight.js
index fcc007d3b5..4799b97e57 100644
--- a/worker/respec-highlight.js
+++ b/worker/respec-highlight.js
@@ -1,7 +1,9 @@
 /* eslint sort-imports: "off" */
 import highlight from "highlight.js/lib/core";
 import abnf from "highlight.js/lib/languages/abnf";
+import bnf from "highlight.js/lib/languages/bnf";
 import css from "highlight.js/lib/languages/css";
+import ebnf from "highlight.js/lib/languages/ebnf";
 import http from "highlight.js/lib/languages/http";
 import javascript from "highlight.js/lib/languages/javascript";
 import json from "highlight.js/lib/languages/json";
@@ -10,11 +12,23 @@ import yaml from "highlight.js/lib/languages/yaml";
 
 highlight.configure({
   tabReplace: "  ", // 2 spaces
-  languages: ["abnf", "css", "http", "javascript", "json", "xml", "yaml"],
+  languages: [
+    "abnf",
+    "bnf",
+    "css",
+    "ebnf",
+    "http",
+    "javascript",
+    "json",
+    "xml",
+    "yaml",
+  ],
 });
 
 highlight.registerLanguage("abnf", abnf);
+highlight.registerLanguage("bnf", bnf);
 highlight.registerLanguage("css", css);
+highlight.registerLanguage("ebnf", ebnf);
 highlight.registerLanguage("http", http);
 highlight.registerLanguage("javascript", javascript);
 highlight.registerLanguage("json", json);