The ai. Subdomain Standard — Draft Specification v1.0
- Version
- 1.0 (Draft)
- Status
- Draft Specification
- Published
- 2026-03-02
- Editor
- NexySync
- License
- CC BY 4.0
Abstract
This specification defines a standard for serving AI-optimized web content via the ai. subdomain prefix. It covers DNS configuration, HTTP headers, HTML meta tags, content format requirements, and conformance criteria for machine-readable web content.
Key Words (RFC 2119)
MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD, SHOULD NOT, RECOMMENDED, MAY, OPTIONAL — interpreted per RFC 2119 and RFC 8174.
Terminology
| Term | Definition |
|---|---|
| Human page | Page served under standard domain (www.example.com), designed for humans |
| AI page | Page served under ai. subdomain (ai.example.com), designed for machines |
| Content parity | AI pages contain same factual information as human pages |
| Token efficiency | Ratio of information-bearing content to total document size (LLM tokens) |
DNS Configuration
- MUST configure ai. subdomain DNS record
- SHOULD resolve to same infrastructure as primary domain
- MUST serve different content based on Host header
Discovery: Meta Tags on Human Pages
| Tag | Level | Description |
|---|---|---|
| <meta name="ai-content" content="[URL]"> | MUST | URL of AI-optimized version |
| <meta name="ai-description" content="..."> | SHOULD | Description for AI agents |
| <link rel="alternate" href="[URL]"> | SHOULD | Alternate link to AI version |
Discovery: Meta Tags on AI Pages
| Tag | Level | Description |
|---|---|---|
| <meta name="ai-optimized" content="true"> | MUST | Identifies page as AI-optimized |
| <meta name="ai-standard-version" content="1.0"> | MUST | Spec version conformance |
| <meta name="ai-format" content="structured-html"> | SHOULD | Content format type |
| <link rel="canonical" href="[human-url]"> | MUST | Canonical link to human page |
| <meta name="robots" content="index, follow"> | SHOULD | Allow crawler discovery |
HTTP Response Headers
| Header | Value | Level |
|---|---|---|
| X-AI-Optimized | true | SHOULD |
| X-AI-Standard-Version | 1.0 | SHOULD |
| Content-Type | text/html; charset=utf-8 | MUST |
Content Format: Required Elements
- MUST: Valid HTML5 with DOCTYPE
- MUST: meta charset="UTF-8"
- MUST: Single h1 element
- MUST: Semantic HTML (article, section, table, dl)
- MUST: Schema.org JSON-LD in head
- MUST: All required meta tags from discovery section
Content Format: Prohibited Elements
- MUST NOT: External CSS stylesheets
- MUST NOT: JavaScript (except JSON-LD)
- MUST NOT: Images, videos, media
- MUST NOT: Navigation, footers, sidebars
- MUST NOT: Cookie banners, popups
- MUST NOT: Tracking, analytics, advertising
- MUST NOT: Marketing language, superlatives
Supported AI Format Types
| Value | MIME Type | Description |
|---|---|---|
| structured-html | text/html | Semantic HTML (default) |
| markdown | text/markdown | Markdown format |
| json | application/json | JSON structured data |
Structured Data Schema Types
| Page Type | Schema.org Type |
|---|---|
| Product/Service | SoftwareApplication or Product |
| Pricing | Offer or PriceSpecification |
| Documentation | TechArticle |
| FAQ | FAQPage |
| Organization | Organization |
Versioning
Semantic versioning (MAJOR.MINOR). MAJOR = breaking changes. MINOR = additive. Current: 1.0 (Draft).
Content Parity
MUST: All features, pricing, technical specs identical to human page. MAY omit: testimonials, marketing copy, CTAs, visual elements.
Security
- MUST: Serve over HTTPS
- MUST NOT: Expose info not on human page
- SHOULD: Implement rate limiting
- MUST NOT: Include executable JavaScript
Conformance Checklist
| # | Requirement | Level |
|---|---|---|
| 1 | ai. subdomain resolves and serves content | MUST |
| 2 | Human pages: ai-content meta tag | MUST |
| 3 | AI pages: ai-optimized meta tag | MUST |
| 4 | AI pages: ai-standard-version meta tag | MUST |
| 5 | AI pages: canonical link to human page | MUST |
| 6 | AI pages: No JavaScript (except JSON-LD) | MUST |
| 7 | AI pages: No external CSS | MUST |
| 8 | AI pages: Schema.org JSON-LD | MUST |
| 9 | Content parity with human page | MUST |
| 10 | Served over HTTPS | MUST |
| 11 | Human pages: link rel="alternate" | SHOULD |
| 12 | AI pages: X-AI-Optimized HTTP header | SHOULD |
References
Normative
- RFC 2119 — Requirement Levels Key Words
- RFC 8174 — Uppercase vs Lowercase in RFC 2119
- HTML Living Standard (WHATWG)
- Schema.org — Structured data vocabulary
Informative
- RFC 9110 — HTTP Semantics
- W3C Data on the Web Best Practices
Changelog
| Version | Date | Changes |
|---|---|---|
| 1.0 (Draft) | 2026-03-02 | Initial draft specification |