utun2/.opencode/context/development/ai/mastra-ai/guides/modular-building.md

Guide: Modular Mastra Building

Purpose: Best practices for structuring a large-scale Mastra implementation.

Last Updated: 2026-01-09

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Core Idea

Modular building ensures that as the project grows, components remain testable, reusable, and easy to navigate. This is achieved by separating logic into specialized directories and using a central registry.

Key Points

• Component Separation: Keep agents, tools, workflows, and scorers in their own top-level directories within src/mastra/.
• Shared Services: Use a shared.ts file to instantiate services (DB, repositories) to prevent circular dependencies between workflows and the main Mastra instance.
• Central Registry: Register all components in src/mastra/index.ts. This is the single source of truth for the Mastra instance.
• Feature-Based Steps: Group related workflow steps into sub-directories (e.g., src/mastra/workflows/v3/steps/) to keep workflow files clean.

Quick Example

// src/mastra/shared.ts
export const services = createServices();

// src/mastra/index.ts
import { services } from './shared';
export const mastra = new Mastra({
  workflows: { myWorkflow },
  agents: { myAgent },
  // ...
});

Reference: src/mastra/index.ts, src/mastra/shared.ts Related:

• concepts/core.md
• guides/workflow-step-structure.md