diff --git a/bun.lock b/bun.lock
index 9b74091..7b617a7 100644
--- a/bun.lock
+++ b/bun.lock
@@ -25,25 +25,26 @@
         "diff-match-patch": "^1.0.5",
         "dompurify": "^3.4.5",
         "elysia": "^1.4.28",
-        "fflate": "^0.8.2",
-        "katex": "^0.16.45",
+        "fflate": "^0.8.3",
+        "katex": "^0.16.47",
         "markdown-it": "^14.1.1",
+        "markdown-it-mark": "^4.0.0",
         "sanitize-html": "^2.17.4",
         "sharp": "^0.34.5",
       },
       "devDependencies": {
-        "@biomejs/biome": "^2.4.14",
-        "@tailwindcss/cli": "^4.2.4",
+        "@biomejs/biome": "^2.4.15",
+        "@tailwindcss/cli": "^4.3.0",
         "@tailwindcss/typography": "^0.5.19",
-        "@types/bun": "^1.3.13",
+        "@types/bun": "^1.3.14",
         "@types/d3": "^7.4.3",
         "@types/diff-match-patch": "^1.0.36",
         "@types/markdown-it": "^14.1.2",
         "@types/sanitize-html": "^2.16.1",
-        "@typescript/native-preview": "^7.0.0-dev.20260507.1",
+        "@typescript/native-preview": "^7.0.0-dev.20260521.1",
         "htmx.org": "^2.0.10",
-        "knip": "^6.12.1",
-        "tailwindcss": "^4.2.4",
+        "knip": "^6.14.1",
+        "tailwindcss": "^4.3.0",
       },
     },
   },
@@ -586,6 +587,8 @@
 
     "markdown-it": ["markdown-it@14.1.1", "", { "dependencies": { "argparse": "^2.0.1", "entities": "^4.4.0", "linkify-it": "^5.0.0", "mdurl": "^2.0.0", "punycode.js": "^2.3.1", "uc.micro": "^2.1.0" }, "bin": { "markdown-it": "bin/markdown-it.mjs" } }, "sha512-BuU2qnTti9YKgK5N+IeMubp14ZUKUUw7yeJbkjtosvHiP0AZ5c8IAgEMk79D0eC8F23r4Ac/q8cAIFdm2FtyoA=="],
 
+    "markdown-it-mark": ["markdown-it-mark@4.0.0", "", {}, "sha512-YLhzaOsU9THO/cal0lUjfMjrqSMPjjyjChYM7oyj4DnyaXEzA8gnW6cVJeyCrCVeyesrY2PlEdUYJSPFYL4Nkg=="],
+
     "mdurl": ["mdurl@2.0.0", "", {}, "sha512-Lf+9+2r+Tdp5wXDXC4PcIBjTDtq4UKjCPMQhKIuzpJNW0b96kVqSwW0bT7FhRSfmAiFYgP+SCRvdrDozfh0U5w=="],
 
     "memoirist": ["memoirist@0.4.0", "", {}, "sha512-zxTgA0mSYELa66DimuNQDvyLq36AwDlTuVRbnQtB+VuTcKWm5Qc4z3WkSpgsFWHNhexqkIooqpv4hdcqrX5Nmg=="],
diff --git a/package.json b/package.json
index f0d2a99..f874101 100644
--- a/package.json
+++ b/package.json
@@ -56,6 +56,7 @@
 		"fflate": "^0.8.3",
 		"katex": "^0.16.47",
 		"markdown-it": "^14.1.1",
+		"markdown-it-mark": "^4.0.0",
 		"sanitize-html": "^2.17.4",
 		"sharp": "^0.34.5"
 	},
diff --git a/public/editor/preview.ts b/public/editor/preview.ts
index 3c9d8d1..70476e5 100644
--- a/public/editor/preview.ts
+++ b/public/editor/preview.ts
@@ -1,10 +1,12 @@
 import DOMPurify from "dompurify";
 import MarkdownIt from "markdown-it";
+import markPlugin from "markdown-it-mark";
 import { katexPlugin } from "../../src/lib/markdown/katex-plugin.ts";
 import { wikilinkPlugin } from "../../src/lib/markdown/wikilink-plugin.ts";
 
 const md = new MarkdownIt({ html: false, linkify: true });
 md.use(wikilinkPlugin);
+md.use(markPlugin);
 md.use(katexPlugin, { throwOnError: false });
 
 // Matches the server-side allowlist closely. The preview is for the author's
diff --git a/public/style.css b/public/style.css
index 1f58f4a..8e7a056 100644
--- a/public/style.css
+++ b/public/style.css
@@ -6,3 +6,11 @@
 .katex {
 	line-height: 1.2;
 }
+
+/* ==highlight== markup */
+mark {
+	background-color: var(--accent-soft);
+	color: inherit;
+	padding: 0.1em 0.2em;
+	border-radius: 2px;
+}
diff --git a/public/tsconfig.json b/public/tsconfig.json
index c0e494a..3db5b7b 100644
--- a/public/tsconfig.json
+++ b/public/tsconfig.json
@@ -3,6 +3,6 @@
 	"compilerOptions": {
 		"lib": ["ESNext", "DOM", "DOM.Iterable"]
 	},
-	"include": ["./**/*.ts"],
+	"include": ["./**/*.ts", "../src/types.d.ts"],
 	"exclude": []
 }
diff --git a/src/lib/markdown.ts b/src/lib/markdown.ts
index 594bfdb..5644b7a 100644
--- a/src/lib/markdown.ts
+++ b/src/lib/markdown.ts
@@ -1,4 +1,5 @@
 import MarkdownIt from "markdown-it";
+import markPlugin from "markdown-it-mark";
 import { headingAnchorPlugin } from "./markdown/heading-anchor-plugin.ts";
 import { type KatexPluginEnv, katexPlugin } from "./markdown/katex-plugin.ts";
 import { sanitizeMarkdownHtml } from "./markdown/sanitize.ts";
@@ -59,6 +60,7 @@ function youtubePlugin(mdi: MarkdownIt): void {
 
 md.use(wikilinkPlugin);
 md.use(headingAnchorPlugin);
+md.use(markPlugin);
 md.use(vizPlugin);
 md.use(katexPlugin, { throwOnError: false });
 md.use(youtubePlugin);
diff --git a/src/types.d.ts b/src/types.d.ts
new file mode 100644
index 0000000..f04e0d7
--- /dev/null
+++ b/src/types.d.ts
@@ -0,0 +1,6 @@
+declare module "markdown-it-mark" {
+	import type MarkdownIt from "markdown-it";
+
+	const plugin: MarkdownIt.PluginSimple;
+	export default plugin;
+}
diff --git a/tests/lib/markdown.test.ts b/tests/lib/markdown.test.ts
index f5a013b..cd538b3 100644
--- a/tests/lib/markdown.test.ts
+++ b/tests/lib/markdown.test.ts
@@ -204,6 +204,29 @@ describe("wikilinks", () => {
 	});
 });
 
+describe("strikethrough", () => {
+	test("renders strikethrough", () => {
+		const { html } = renderMarkdown("~~deleted~~");
+		expect(html).toContain("<s>");
+		expect(html).toContain("deleted");
+	});
+});
+
+describe("highlights", () => {
+	test("renders highlight markup", () => {
+		const { html } = renderMarkdown("This is ==highlighted== text.");
+		expect(html).toContain("<mark>");
+		expect(html).toContain("highlighted");
+	});
+
+	test("highlight does not collide with other inline", () => {
+		const { html } = renderMarkdown("**bold** and ==highlight== and `code`");
+		expect(html).toContain("<mark>");
+		expect(html).toContain("<strong>");
+		expect(html).toContain("<code>");
+	});
+});
+
 describe("heading anchors", () => {
 	test("attaches id to rendered headings", () => {
 		const { html } = renderMarkdown("# Hello World\n\n## Another One");