---
title: "@dualmark/core"
description: Framework-agnostic primitives for AEO infrastructure.
---

Zero runtime dependencies. ESM + CJS. Strict TypeScript.

<Tabs items={["bun", "npm", "yarn"]}>
<Tab value="bun">
```bash
bun add @dualmark/core
```
</Tab>
<Tab value="npm">
```bash
npm install @dualmark/core
```
</Tab>
<Tab value="yarn">
```bash
yarn add @dualmark/core
```
</Tab>
</Tabs>

## Content negotiation

```ts
import { parseAcceptHeader, negotiateFormat } from "@dualmark/core";
```

### `parseAcceptHeader(accept: string): ParsedMediaType[]`

Parses an `Accept` header per RFC 7231 §5.3.2, returning entries sorted by quality factor.

### `negotiateFormat(accept: string): "html" | "markdown" | null`

Picks the best response format. Returns `null` when neither HTML nor markdown is acceptable (caller should respond `406`).

## AI bot detection

```ts
import { AI_BOTS, detectAIBot } from "@dualmark/core";
```

### `detectAIBot(userAgent: string): AIBotInfo`

Returns `{ isBot, name, vendor, purpose, entry }`. The registry covers 19 known crawlers across OpenAI, Anthropic, Google, Perplexity, Common Crawl, and more -- see [spec/ai-bot-detection](/docs/spec/ai-bot-detection).

### `AI_BOTS: AIBotEntry[]`

The full registry, exported for inspection or extension.

## Markdown response

```ts
import { markdownResponse, injectMarkdownAlternateLink } from "@dualmark/core";
```

### `markdownResponse(body, options?): Response`

Builds a `Response` with all required AEO headers (`Content-Type`, `X-Markdown-Tokens`, `X-Robots-Tag`, `Vary`, `X-AEO-Version`, `X-Content-Type-Options`, `Cache-Control`).

```ts
markdownResponse("# Hello", {
  cacheControl: "public, max-age=3600",
  noindex: true,
  redirectFrom: "/old",
  redirectTo: "/new",
  extraHeaders: { "X-Custom": "value" },
});
```

### `injectMarkdownAlternateLink(response, htmlPath, mdPath): Response`

Returns a new `Response` with the `Link rel="alternate"; type="text/markdown"` header appended.

## Path utilities

```ts
import { toMarkdownPath, toMarkdownUrl } from "@dualmark/core";

toMarkdownPath("/blog/post");           // -> "/blog/post.md"
toMarkdownPath("/");                    // -> "/index.md"
toMarkdownPath("/blog/post.md");        // -> "/blog/post.md"  (idempotent)

toMarkdownUrl("https://x.com/blog?q=1"); // -> "https://x.com/blog.md?q=1"
```

Both helpers are idempotent on already-`.md` inputs.

## Token estimation

```ts
import { estimateTokens } from "@dualmark/core";
```

Whitespace-split counter -- fast, zero-dep, good enough for `X-Markdown-Tokens`.

## Text utilities

```ts
import { normalizeUnicode, cleanBody, slugToTitle, fmtDate, joinLines } from "@dualmark/core";
```

For writing markdown converters by hand. See source for signatures.

## Composition helpers

```ts
import { listingToMarkdown, renderRelatedLinks, renderFAQSection } from "@dualmark/core";
```

Common markdown patterns: collection listings, related-links blocks, FAQ rendering.

## llms.txt

```ts
import { renderLlmsTxt } from "@dualmark/core";

const body = renderLlmsTxt({
  brandName: "Acme",
  description: "Acme's docs.",
  sections: [
    { title: "Pages", links: [{ title: "Home", href: "/" }] },
  ],
});
```

## Constant

```ts
import { AEO_SPEC_VERSION } from "@dualmark/core";
// -> "1.0"
```