/building-dbt-semantic-layer

name: building-dbt-semantic-layer
description: Use when creating or modifying dbt Semantic Layer components — semantic models, metrics, dimensions, entities, measures, or time spines. Covers MetricFlow configuration, metric types (simple, derived, cumulative, ratio, conversion), and validation for both latest and legacy YAML specs.
user-invocable: false
metadata:
  author: dbt-labs

Building the dbt Semantic Layer

This skill guides the creation and modification of dbt Semantic Layer components: semantic models, entities, dimensions, and metrics.

• **Semantic models** - Metadata configurations that define how dbt models map to business concepts
• **Entities** - Keys that identify the grain of your data and enable joins between semantic models
• **Dimensions** - Attributes used to filter or group metrics (categorical or time-based)
• **Metrics** - Business calculations defined on top of semantic models (e.g., revenue, order count)

Additional Resources

• [Time Spine Setup](references/time-spine.md) - Required for time-based metrics and aggregations
• [Best Practices](references/best-practices.md) - Design patterns and recommendations for semantic models and metrics
• [Latest Spec Authoring Guide](references/latest-spec.md) - Full YAML reference for dbt Core 1.12+ and Fusion
• [Legacy Spec Authoring Guide](references/legacy-spec.md) - Full YAML reference for dbt Core 1.6-1.11

Determine Which Spec to Use

There are two versions of the Semantic Layer YAML spec:

• **Latest spec** - Semantic models are configured as metadata on dbt models. Simpler authoring. Supported by dbt Core 1.12+ and Fusion.
• **Legacy spec** - Semantic models are defined as separate top-level resources. Uses measures as building blocks for metrics. Supported by dbt Core 1.6 through 1.11. Also supported by Core 1.12+ for backwards compatibility.

Step 1: Check for Existing Semantic Layer Config

Look for existing semantic layer configuration in the project:

• Top-level `semantic_models:` key in YAML files → **legacy spec**
• `semantic_model:` block nested under a model → **latest spec**

Step 2: Route Based on What You Found

**If semantic layer already exists:**

1. Determine which spec is currently in use (legacy or latest) 2. Check dbt version for compatibility:

• **Legacy spec + Core 1.6-1.11** → Compatible. Use [legacy spec guide](references/legacy-spec.md).
• **Legacy spec + Core 1.12+ or Fusion** → Compatible, but offer to upgrade first using `uvx dbt-autofix deprecations --semantic-layer` or the [migration guide](https://docs.getdbt.com/docs/build/latest-metrics-spec). They don't have to upgrade; continuing with legacy is fine.
• **Latest spec + Core 1.12+ or Fusion** → Compatible. Use [latest spec guide](references/latest-spec.md).
• **Latest spec + Core <1.12** → Incompatible. Help them upgrade to dbt Core 1.12+.

**If no semantic layer exists:**

1. **Core 1.12+ or Fusion** → Use [latest spec guide](references/latest-spec.md) (no need to ask). 2. **Core 1.6-1.11** → Ask if they want to upgrade to Core 1.12+ for the easier authoring experience. If yes, help upgrade. If no, use [legacy spec guide](references/legacy-spec.md).

Step 3: Follow the Spec-Specific Guide

Once you know which spec to use, follow the corresponding guide's implementation workflow (Steps 1-4) for all YAML authoring. The guides are self-contained with full examples.

**Minimal latest spec example** (dbt Core 1.12+ / Fusion) — use this as your starting point to avoid guessing the structure:

# models/fct_orders.yml
models:
  - name: fct_orders
    semantic_model:
      enabled: true
    agg_time_dimension: order_date
    columns:
      - name: order_id
        entity:
          type: primary
          name: order
      - name: customer_id
        entity:
          type: foreign
          name: customer
      - name: order_date
        granularity: day
        dimension:
          type: time
      - name: status
        dimension:
          type: categorical
    metrics:
      - name: total_revenue
        type: simple
        label: Total Revenue
        agg: sum
        expr: amount

**Minimal legacy spec example** (dbt Core 1.6–1.11) — use this if the project is on an older version:

# models/sem_orders.yml
semantic_models:
  - name: orders
    model: ref('fct_orders')
    defaults:
      agg_time_dimension: order_date
    entities:
      - name: order
        type: primary
        expr: order_id
    dimensions:
      - name: order_date
        type: time
        type_params:
          time_granularity: day
    measures:
      - name: revenue
        agg: sum
        expr: amount

metrics:
  - name: total_revenue
    type: simple
    label: Total Revenue
    type_params:
      measure: revenue

Entry Points

Users may ask questions related to building metrics with the semantic layer in a few different ways. Here are the common entry points to look out for:

Business Question First

When the user describes a metric or analysis need (e.g., "I need to track customer lifetime value by segment"):

1. Search project models or existing semantic models by name, description, and column names for relevant candidates 2. Present top matches with brief context (model name, description, key columns) 3. User confirms which model(s) / semantic models to build on / extend / update 4. Work backwards from users need to define entities, dimensions, and metrics

Model First

When the user specifies a model to expose (e.g., "Add semantic layer to `customers` model"):

1. Read the model SQL and existing YAML config 2. Identify the grain (primary key / entity) 3. Suggest dimensions based on column types and names 4. Ask what metrics the user wants to define

Both paths converge on the same implementation workflow.

Open Ended

User asks to build the semantic layer for a project or models that are not specified. ("Build the semantic layer for my project")

1. Identify high importanc