# Metric Semantic Layer: How Lyft Governs and Scales Key Data Definitions

[Lyft](https://yomu.fyi/company/lyft) · Iraklikhorguani · Jun 10, 2026

**Type:** Problem & solution

## Summary

As Lyft scaled, different teams developed conflicting definitions for key business metrics due to the lack of centralized version control and shared standards. To resolve this, Lyft implemented an internal Metric Semantic Layer as a Python package that stores authoritative metric definitions in YAML files with Jinja SQL templates. The system restricts onboarding to Golden Metrics used across multiple applications, requiring team-based approval from both Business and Operational Owners for any definition changes. Standardized definitions are exposed through Python APIs, integrated into the Amundsen data catalog and self-service user interfaces, and surfaced to AI tools via a Model Context Protocol.

## Context

As Lyft grew, products and teams evolved without centralized version control or a shared metric standard. Consequently, different teams created inconsistent definitions for identical metrics, allowing outdated definitions to influence operational decisions, key forecasts, and hypothesis testing.

## Approach / What changed

Lyft built the Metric Semantic Layer (MSL) as a Python package using YAML configurations and Jinja SQL templates to decouple metric logic across granularities and dimensions. Governance is enforced by onboarding only Golden Metrics with at least two use cases and mandating dual team-level ownership across Business and Operational owners for metric changes. MSL definitions are exposed via Python APIs, automated downstream code refactoring, Amundsen catalog integration, a no-code UI, and an MCP server for AI workflows.

## Takeaways

- Golden Metrics require at least two distinct use cases to qualify for onboarding into MSL, preventing niche metrics from adding unnecessary governance overhead.
- Metric modifications mandate dual sign-off from a team-based Business Owner responsible for metric health and an Operational Owner responsible for underlying data pipelines and data quality.
- Exposing YAML metric definitions via a Model Context Protocol (MCP) enables natural-language querying by AI agents and BI tools while reducing hallucinations.

**Tags:** [Architecture](https://yomu.fyi/topic/architecture), [Data Pipelines](https://yomu.fyi/topic/data-pipelines), [LLMs](https://yomu.fyi/topic/llm), [Python](https://yomu.fyi/topic/python)

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