OpenFacet offers free, real-time access to natural GIA-certified round diamond prices via a structured JSON API. Data includes current DCX index, per-carat matrices, and depth across clarity/color bands. Unlike closed or credentialed platforms, OpenFacet provides open, unauthenticated, and machine-ready data feeds without account setup or XML legacy formats.

The API supports valuation, algorithmic pricing, and liquidity modeling by exposing core components of OpenFacet’s transparent pricing methodology. All responses are JSON-formatted and timestamped in UTC.

REST API Endpoints

Endpoints are served from: https://data.openfacet.net/.

GET /index.json – Composite Index & Basket

Returns the current Diamond Composite Index (DCX) and a representative basket of actively traded specifications.

Example: /index.json

Sample Response

{
  "dcx": 3568.6,
  "specs": [
    {
      "carat": 0.5,
      "clarity": "SI1",
      "color": "H",
      "cut": "Excellent",
      "log": 7.428,
      "per_carat": 1682.38,
      "price": 841.19,
      "weight": 0.22
    },
    ...
  ],
  "trend": 0.13,
  "ts": "2025-05-19T13:26:49Z"
}

Fields

• dcx: Composite per-carat price in USD.

• specs[]: Sample stones with:

  • price: Total price in USD
  • per_carat: USD per carat
  • log: $\log(\text{price})$ for interpolation
  • weight: Basket contribution

• trend: 24h change in dcx, in percent (e.g. 0.13 = +0.13%)

• ts: Timestamp in ISO 8601 format

GET /matrix.json – Price Matrices

Returns per-carat log price matrices across clarity and color, grouped by fixed carat bands.

Example: /matrix.json

Key Fields

• l: Map of carat band → flat array of $\log(\text{per-carat price})$ values. Each array is of length rows × cols, where:
  • rows = number of color grades (r)
  • cols = number of clarity grades (c)
• c: Clarity grade list (columns)
• r: Color grade list (rows)
• s: Shape [rows, cols] = [len(r), len(c)]

Price Calculation

To compute per-carat price:

$$ \text{price} = \exp(\log_\text{price}) $$

To interpolate $\log(\text{per-carat price})$ for non-discrete carat weights:

$$ \log_i = (1 - \lambda) \cdot \log(p_1) + \lambda \cdot \log(p_2) $$

Where:

• $p_1, p_2$ are per-carat prices at carat bands $c_1, c_2$
• $\lambda = \frac{c - c_1}{c_2 - c_1}$, with $c$ the target carat

After interpolation, apply Math.exp(log_i) to obtain the interpolated per-carat price.

GET /depth.json – Market Depth

Reports inventory depth across dimensions of carat, color, and clarity. Useful for liquidity-aware models or filtering.

Example: /depth.json

Structure

• clarity[carat][clarity]: Listings count per clarity grade at given carat
• color[carat][color]: Listings count per color grade at given carat
• colclar[color][clarity]: Total listings for each color × clarity pair
• ts: Snapshot timestamp

Example

"1.0": {
  "VS2": 1232
}

There are 1232 listings for 1.0ct VS2 diamonds at the snapshot time.

MCP Server

The same diamond pricing data is also exposed via a Model Context Protocol (MCP)–compliant remote server at: https://mcp.openfacet.net/ for AI agents and LLM applications.

This remote MCP endpoint provides programmatic access to:

• Interpolated diamond prices (get_diamond_price) – Real-time pricing with interpolation across carat, color, and clarity
• DCX index values (get_dcx_index) – Composite market trends and 24h changes
• Market depth analytics (get_market_depth) – Inventory counts and liquidity data

Example

Requesting a diamond price quote for a 1.23ct G VS2 round diamond:

{
  "jsonrpc": "2.0",
  "id": 1,
  "method": "tools/call",
  "params": {
    "name": "get_diamond_price",
    "arguments": {
      "carat": 1.23,
      "color": "G",
      "clarity": "VS2"
    }
  }
}

Response:

{"jsonrpc":"2.0","id":1,"result":{"content":[{"type":"text","text":"💎 **Diamond Price Quote**\n\n**Specifications:**\n• Carat: 1.23ct\n• Color: G\n• Clarity: VS2\n• Shape: round\n\n**Pricing:**\n• Per Carat: $4,490\n• Total Price: $5,522.7\n\n*Prices from OpenFacet.net API*"}],"_meta":{"timestamp":"2025-07-09T03:22:28.407Z","source":"OpenFacet.net API"}}

The server is unauthenticated and supports automatic discovery via standard tools/list calls. Responses follow MCP 2025-06-18 specification and use JSON-RPC 2.0 with structured content format.

For developers integrating with AI systems, the MCP server provides the same underlying data as the REST endpoints above, but with built-in interpolation and a protocol designed for LLM tool use.

Data Freshness

Snapshots are updated periodically, typically once per 24h. Check the ts field in each response to ensure data recency. MCP tool responses are based on the same underlying snapshot datasets.

For methodology details, see the OpenFacet & DCX Methodology page.

Disclaimer: The Diamond Composite Index (DCX) is a model-based benchmark constructed from public retail listings. It does not represent executable prices or financial advice. All data is filtered, interpolated, and smoothed for index use. Use at your own discretion. GIA is a registered trademark of the Gemological Institute of America. This site is not affiliated with, endorsed by, or associated with GIA.