> ## Documentation Index
> Fetch the complete documentation index at: https://learn.orbexa.io/llms.txt
> Use this file to discover all available pages before exploring further.

# OTR four-layer architecture overview

> OTR's four-layer architecture explained in detail — Signal Collection, Scoring Engine, ID Generation, and Verification API components.

# OTR Architecture Overview

## 2.1 Four-Layer Architecture

```
+----------------------------------------------------------+
|                Verification Layer                         |
|  REST API . .well-known/otr/verify . MCP Server          |
|  AI agents and developers query trust scores here        |
+----------------------------------------------------------+
|                Identity Layer                             |
|  OTR-ID . Trust Badges (PLATINUM/GOLD/SILVER/BRONZE)     |
|  Each domain receives a unique identifier and badge      |
+----------------------------------------------------------+
|                Scoring Layer                              |
|  Six-Dimension Model . Weight System . Site-Type Adapt.  |
|  77 signals weighted to produce a 0-100 score           |
+----------------------------------------------------------+
|                Collection Layer                           |
|  DNS . SSL . HTML . Fingerprints . GLEIF . Wikidata . SEC|
|  Automatic collection of public signals from many sources|
+----------------------------------------------------------+
```

## 2.2 Data Flow

The complete journey of a domain from initial submission to a trust score:

```
Domain Submitted
  |
  v
Collection Layer: Multi-Stage Pipeline
  +- DNS checks (DNSSEC/DMARC/SPF/DKIM/CAA and more)
  +- HTML scan (SSL/structured data/policy pages/llms.txt)
  +- Technology fingerprint detection (2,400+ known technologies)
  +- Site classification (ecommerce/SaaS/non-commercial, 13 subcategories)
  +- Policy depth analysis (privacy/returns/terms of service quality)
  +- External data sources (GLEIF/Wikidata/Finnhub/SEC)
  +- Data integration (multi-source merge)
  |
  v
Scoring Layer: Scorer
  +- Read all signals
  +- Group by dimension (V/S/G/T/D/F)
  +- Apply weight matrix (adapted by site type: ecommerce/saas/authorized)
  +- Compute per-dimension scores and total score
  +- Assign badge
  |
  v
Identity Layer: OTR-ID Generation
  +- Format: OTR-{hash}
  +- Links domain, score, and badge
  |
  v
Verification Layer: API Publication
  +- GET /api/otr/verify/{domain}
  +- GET /.well-known/otr/verify
  +- MCP Server: @otr-protocol/mcp-server
```

## 2.3 Relationship with Other Commerce Protocols

OTR does not operate in isolation. It serves as the **trust infrastructure** within the agentic commerce ecosystem:

```
                          +-----------+
                          | AI Agent  |
                          +-----+-----+
                                |
                   +------------+------------+
                   |            |            |
             +-----v----+ +----v----+ +----v----+
             |   UCP    | |   ACP   | |   MCP   |
             | Product  | | Orders  | |  Tool   |
             | Discovery| | Payment | | Connect |
             +-----+----+ +----+----+ +----+----+
                   |            |            |
                   +------------+------------+
                                |
                         +------v------+
                         |    OTR      |
                         | Trust Score |
                         +-------------+
```

* **OTR and UCP**: Before an AI agent browses products via UCP, it checks the merchant's OTR trust score. Low-scoring merchants may have their products deprioritized.
* **OTR and ACP**: Before an AI agent places an order on behalf of a consumer, the OTR trust badge is one of the inputs to its risk assessment.
* **OTR and MCP**: ORBEXA provides an OTR MCP Server so AI assistants can directly call the `verify_domain` tool to look up trust scores.

## 2.4 Site-Type Adaptation

Not all websites are e-commerce stores. OTR automatically adjusts scoring weights based on site type:

| Site Type      | D-Dimension Weight | F-Dimension Weight | Typical Characteristics                   |
| -------------- | ------------------ | ------------------ | ----------------------------------------- |
| **ecommerce**  | High               | High               | Has products, shopping cart, payment      |
| **saas**       | Medium             | Low                | Software service, subscription model      |
| **authorized** | Varies             | Varies             | Merchant has authorized deep verification |

Classification is performed automatically by the fingerprint engine, based on the site's technology stack, page structure, and functional features.

***

**Next Chapter**: [V/S Dimensions — Verification and Security Signals](/en/book-2/ch3-verification-signals) — 13 verification signals + 15 security signals