IANA Permanent Message Header Field Registration =============================================== Header Field Name: x-fcs-version x-protocol-family x-trust-mode x-behavioral-tracking x-trust-lineage x-intention-signal x-semantic-context x-discovery-inline Applicable Protocol: HTTP Status: Provisional Author/Change Controller: Contextual Ads Initiative Specification Document: https://contextual-ads.ai/spec/v1.0 Related Information: https://contextual-ads.ai/.well-known/agent-ad.json --- ## 1. Header Field Definitions ### 1.1 x-fcs-version Field Name: x-fcs-version Protocol: HTTP (RFC 7230) Status: Provisional Description: Identifies the Field-Coherence Substrate (FCS) protocol version Reference: https://contextual-ads.ai/spec/v1.0#section-2.3 Syntax: x-fcs-version = protocol-version protocol-version = 1*DIGIT "." 1*DIGIT ["." 1*DIGIT] Example: x-fcs-version: 2.0 x-fcs-version: 1.0.0 Purpose: Enables version negotiation for FCS-compatible systems. Used by AI agents, browsers, and advertising platforms to determine protocol compatibility. --- ### 1.2 x-protocol-family Field Name: x-protocol-family Protocol: HTTP (RFC 7230) Status: Provisional Description: Identifies the protocol family (e.g., FCS-1.0, FCS-2.0, CAP) Reference: https://contextual-ads.ai/spec/v1.0#section-2.3 Syntax: x-protocol-family = family-name family-name = token Example: x-protocol-family: FCS-2.0 x-protocol-family: CAP Purpose: Distinguishes between protocol families within the FCS ecosystem. Enables specialized handling for advertising (CAP), semantic discovery, or trust verification protocols. --- ### 1.3 x-trust-mode Field Name: x-trust-mode Protocol: HTTP (RFC 7230) Status: Provisional Description: Declares the trust enforcement mode for the current transaction Reference: https://contextual-ads.ai/spec/v1.0#section-4 Syntax: x-trust-mode = trust-policy trust-policy = "no-behavioral-tracking" / "verified-lineage" / "strict" Example: x-trust-mode: no-behavioral-tracking Purpose: Explicitly signals privacy guarantees. When set to "no-behavioral-tracking", indicates that no user profiling, cookies, or cross-site tracking is performed. Enables compliance verification for GDPR, CCPA, and DMA regulations. --- ### 1.4 x-behavioral-tracking Field Name: x-behavioral-tracking Protocol: HTTP (RFC 7230) Status: Provisional Description: Boolean indicator of behavioral tracking status Reference: https://contextual-ads.ai/spec/v1.0#section-4.1 Syntax: x-behavioral-tracking = "true" / "false" Example: x-behavioral-tracking: false Purpose: Machine-readable attestation that no behavioral tracking occurs. Differs from x-trust-mode by providing a simple boolean that agents can programmatically verify. Required for Contextual Ads Protocol compliance. Security Considerations: This header is a declaration, not a cryptographic proof. Trust verification requires x-trust-lineage inspection and external auditing. --- ### 1.5 x-trust-lineage Field Name: x-trust-lineage Protocol: HTTP (RFC 7230) Status: Provisional Description: Semicolon-separated chain of processing steps for trust verification Reference: https://contextual-ads.ai/spec/v1.0#section-2.1 Syntax: x-trust-lineage = step *(";" step) step = origin ":" method ":" timestamp origin = host / domain method = token timestamp = ISO8601-datetime Example: x-trust-lineage: agent-mcp.org:query-semantic:2025-12-01T14:30:00Z;contextual-ads.ai:protocol-serve:2025-12-01T14:30:01Z Purpose: Provides full provenance chain for auditing. Each processing step appends its origin, method, and timestamp. Enables regulatory compliance (EU AI Act Article 52, DMA Articles 5-6) by making data flows transparent and auditable. Privacy Considerations: Trust lineage should not include user identifiers or personal data. Only system origins, processing methods, and timestamps should be logged. --- ### 1.6 x-intention-signal Field Name: x-intention-signal Protocol: HTTP (RFC 7230) Status: Provisional Description: JSON object describing explicit user intention derived from context Reference: https://contextual-ads.ai/spec/v1.0#section-2.1 Syntax: x-intention-signal = JSON-object JSON-object = per RFC 8259 Example: x-intention-signal: {"primary":"purchase","domain":"mcp-servers","confidence":0.87,"source":"query-semantic"} Structure: { "primary": "discovery|purchase|compare|learn|entertain", "domain": "product-category-or-topic", "confidence": 0.0-1.0, "context": "brief-description", "source": "content-analysis|user-query|page-metadata" } Purpose: Enables intention-based advertising without behavioral tracking. Intention is derived from current query/page context only, not from user history. Replaces cookie-based targeting with semantic matching. Privacy Guarantee: Signal derived from current context only. No user identifiers, browsing history, or demographic profiling included. --- ### 1.7 x-semantic-context Field Name: x-semantic-context Protocol: HTTP (RFC 7230) Status: Provisional Description: Comma-separated semantic tags describing current page/query context Reference: https://contextual-ads.ai/spec/v1.0#section-2.1 Syntax: x-semantic-context = tag *("," tag) tag = key ":" value key = token value = token Example: x-semantic-context: topic:mcp-servers,category:database,intent:discovery,stage:evaluation Purpose: Captures semantic meaning of current content for ad matching. Unlike behavioral ads (which target users), semantic context targets content. Enables privacy- preserving relevance without tracking. Semantic Dimensions: - topic: High-level category - category: Specific subcategory - intent: User goal (discovery, purchase, etc.) - stage: Journey stage (evaluation, decision, etc.) --- ### 1.8 x-discovery-inline Field Name: x-discovery-inline Protocol: HTTP (RFC 7230) Status: Provisional Description: User journey stage indicator Reference: https://contextual-ads.ai/spec/v1.0#section-2.2 Syntax: x-discovery-inline = stage stage = "discovery" / "evaluation" / "decision" / "post-purchase" Example: x-discovery-inline: evaluation Purpose: Indicates where user is in decision journey. Enables advertisers to tailor messaging (e.g., comparison tools during evaluation, tutorials post-purchase) without tracking user across sites. --- ## 2. Protocol Overview The Field-Coherence Substrate (FCS) protocol family defines HTTP headers for privacy-preserving contextual advertising and semantic discovery. FCS enables: 1. **Intention-based targeting** without behavioral tracking 2. **Transparent provenance** via trust lineage chains 3. **Semantic discovery** for AI agents and browsers 4. **Regulatory compliance** by design (GDPR, CCPA, DMA, AI Act) ### 2.1 Core Principle Traditional advertising tracks *users* across sites. FCS tracks *context* within a single query/page. This architectural difference eliminates privacy risks while maintaining relevance. ### 2.2 Trust Model Every FCS transaction includes: - x-behavioral-tracking: false (privacy attestation) - x-trust-lineage: full processing chain (auditability) - x-intention-signal: explicit context (no inference from history) --- ## 3. Security Considerations ### 3.1 Header Spoofing Servers must validate FCS headers to prevent spoofing. Recommended: - Verify x-trust-lineage timestamps (reject stale/future timestamps) - Check origin domains against trusted registries - Reject x-behavioral-tracking: false if tracking detected ### 3.2 Privacy Leakage Headers must not contain: - User identifiers (cookies, session IDs, device fingerprints) - Personal data (names, emails, demographics) - Browsing history or cross-site references ### 3.3 Trust Verification x-trust-lineage provides transparency but not cryptographic proof. For high-trust scenarios, consider: - Digital signatures on trust lineage steps - External auditing of processing chains - Real-time verification via trusted third parties --- ## 4. IANA Considerations This document requests registration of eight HTTP header fields in the Permanent Message Header Field Registry: 1. x-fcs-version 2. x-protocol-family 3. x-trust-mode 4. x-behavioral-tracking 5. x-trust-lineage 6. x-intention-signal 7. x-semantic-context 8. x-discovery-inline Status: Provisional (pending community review and adoption) Target: Promotion to Standard after 12-24 months deployment evidence --- ## 5. Compatibility ### 5.1 Backwards Compatibility FCS headers are optional. Legacy systems can ignore them without breaking functionality. Graceful degradation: - If FCS headers absent → fall back to standard HTTP behavior - If x-behavioral-tracking: true → reject or warn (policy-dependent) ### 5.2 Forward Compatibility FCS versioning (x-fcs-version) enables protocol evolution. Servers should: - Support multiple versions during transition periods - Reject unsupported versions with clear error messages - Document version-specific behavior changes --- ## 6. Implementation Guidelines ### 6.1 Publishers To implement FCS-compliant contextual advertising: 1. Analyze current page/query for semantic context 2. Generate x-intention-signal from context (not user history) 3. Set x-behavioral-tracking: false 4. Include x-trust-lineage with origin and timestamp 5. Pass headers to ad platform via x-semantic-context Example (Cloudflare Worker): ```javascript export default { async fetch(request) { const context = analyzePageContext(await request.text()); return new Response(content, { headers: { 'x-fcs-version': '2.0', 'x-protocol-family': 'CAP', 'x-trust-mode': 'no-behavioral-tracking', 'x-behavioral-tracking': 'false', 'x-trust-lineage': `${origin}:content-semantic:${timestamp}`, 'x-intention-signal': JSON.stringify(context.intention), 'x-semantic-context': context.tags.join(',') } }); } }; ``` ### 6.2 AI Agents To consume FCS headers: 1. Parse x-intention-signal to understand user intent 2. Verify x-behavioral-tracking: false before displaying content 3. Inspect x-trust-lineage for provenance transparency 4. Use x-semantic-context for relevance filtering --- ## 7. Related Standards - RFC 7230: Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing - RFC 8259: JSON Data Interchange Format - RFC 8615: Well-Known URIs - GDPR Article 25: Data protection by design - EU AI Act Article 52: Transparency obligations for AI systems - DMA Articles 5-6: Ads transparency and data portability --- ## 8. References Normative References: - Contextual Ads Protocol v1.0: https://contextual-ads.ai/spec/v1.0 - FCS-2.0 Specification: https://contextual-ads.ai/spec/fcs-2.0 Informative References: - Protocol Discovery: https://contextual-ads.ai/.well-known/agent-ad.json - Advertiser Registry: https://contextual-ads.ai/registry/advertisers - Research Papers: https://contextual-ads.ai/research/ --- ## 9. Author's Address Contextual Ads Initiative Email: spec@contextual-ads.ai URI: https://contextual-ads.ai For technical questions: spec@contextual-ads.ai For registry submissions: registry@contextual-ads.ai For research collaboration: research@contextual-ads.ai --- ## 10. Appendix A: Full Example Request with FCS headers: ``` GET /discover?q=database+mcp+servers HTTP/1.1 Host: agent-mcp.org x-fcs-version: 2.0 x-protocol-family: CAP x-trust-mode: no-behavioral-tracking x-behavioral-tracking: false x-trust-lineage: agent-mcp.org:query-semantic:2025-12-01T20:00:00Z x-intention-signal: {"primary":"discovery","domain":"mcp-servers","confidence":0.90} x-semantic-context: topic:mcp-servers,category:database,intent:discovery x-discovery-inline: evaluation ``` Response with FCS headers: ``` HTTP/1.1 200 OK Content-Type: application/json x-fcs-version: 2.0 x-protocol-family: CAP x-trust-mode: no-behavioral-tracking x-behavioral-tracking: false x-trust-lineage: agent-mcp.org:query-semantic:2025-12-01T20:00:00Z;contextual-ads.ai:protocol-serve:2025-12-01T20:00:01Z { "results": [...], "contextual_ads": [{ "advertiser": "PostgreSQL MCP Server", "relevance_score": 0.94, "trust_verified": true, "no_tracking": true }] } ``` --- ## 11. Changelog - 2025-12-01: Initial draft for IANA submission - Status: Provisional pending community feedback - Target: Finalize by Q1 2026 with deployment evidence --- END OF IANA SUBMISSION DRAFT