Chapter 4: Workflows and Control Flow

Welcome to Chapter 4: Workflows and Control Flow. In this part of Mastra Tutorial: TypeScript Framework for AI Agents and Workflows, you will build an intuitive mental model first, then move into concrete implementation details and practical production tradeoffs.

Mastra workflows provide deterministic orchestration when autonomous loops are not enough.

Workflow Controls

Control	Use Case
.then()	linear stage execution
.branch()	conditional routing
.parallel()	independent concurrent tasks
suspend/resume	human approval or async wait states

Decision Rule

Use workflows when you need strict ordering, approvals, or compliance constraints.

Production Pattern

1. agent drafts plan
2. workflow runs approval gates
3. tools execute with policy checks
4. workflow commits output and telemetry

Source References

• Mastra Workflows Docs
• Suspend and Resume

Summary

You now know when and how to move from free-form agents to deterministic workflow control.

Next: Chapter 5: Memory, RAG, and Context

Source Code Walkthrough

explorations/network-validation-bridge.ts

The customCheck function in explorations/network-validation-bridge.ts handles a key part of this chapter's functionality:

 * Custom validation check from a function
 */
export function customCheck(
  id: string,
  name: string,
  fn: () => Promise<{ success: boolean; message: string; details?: Record<string, unknown> }>,
): ValidationCheck {
  return {
    id,
    name,
    async check() {
      const start = Date.now();
      const result = await fn();
      return { ...result, duration: Date.now() - start };
    },
  };
}

/**
 * File exists check
 */
export function fileExists(path: string): ValidationCheck {
  return {
    id: `file-exists-${path}`,
    name: `File Exists: ${path}`,
    async check() {
      const start = Date.now();
      try {
        const fs = await import('fs/promises');
        await fs.access(path);
        return {
          success: true,

This function is important because it defines how Mastra Tutorial: TypeScript Framework for AI Agents and Workflows implements the patterns covered in this chapter.

explorations/network-validation-bridge.ts

The fileExists function in explorations/network-validation-bridge.ts handles a key part of this chapter's functionality:

 * File exists check
 */
export function fileExists(path: string): ValidationCheck {
  return {
    id: `file-exists-${path}`,
    name: `File Exists: ${path}`,
    async check() {
      const start = Date.now();
      try {
        const fs = await import('fs/promises');
        await fs.access(path);
        return {
          success: true,
          message: `File ${path} exists`,
          duration: Date.now() - start,
        };
      } catch {
        return {
          success: false,
          message: `File ${path} does not exist`,
          duration: Date.now() - start,
        };
      }
    },
  };
}

/**
 * File contains pattern check
 */
export function fileContains(path: string, pattern: string | RegExp): ValidationCheck {
  return {

This function is important because it defines how Mastra Tutorial: TypeScript Framework for AI Agents and Workflows implements the patterns covered in this chapter.

explorations/network-validation-bridge.ts

The fileContains function in explorations/network-validation-bridge.ts handles a key part of this chapter's functionality:

 * File contains pattern check
 */
export function fileContains(path: string, pattern: string | RegExp): ValidationCheck {
  return {
    id: `file-contains-${path}`,
    name: `File Contains Pattern: ${path}`,
    async check() {
      const start = Date.now();
      try {
        const fs = await import('fs/promises');
        const content = await fs.readFile(path, 'utf-8');
        const matches = typeof pattern === 'string' ? content.includes(pattern) : pattern.test(content);

        return {
          success: matches,
          message: matches
            ? `File ${path} contains expected pattern`
            : `File ${path} does not contain expected pattern`,
          duration: Date.now() - start,
        };
      } catch (error: any) {
        return {
          success: false,
          message: `Could not read file ${path}: ${error.message}`,
          duration: Date.now() - start,
        };
      }
    },
  };
}

// ============================================================================

This function is important because it defines how Mastra Tutorial: TypeScript Framework for AI Agents and Workflows implements the patterns covered in this chapter.

explorations/network-validation-bridge.ts

The runValidation function in explorations/network-validation-bridge.ts handles a key part of this chapter's functionality:

// ============================================================================

async function runValidation(
  config: NetworkValidationConfig,
): Promise<{ passed: boolean; results: ValidationResult[] }> {
  const results: ValidationResult[] = [];

  if (config.parallel) {
    // Run all checks in parallel
    const checkResults = await Promise.all(config.checks.map(check => check.check()));
    results.push(...checkResults);
  } else {
    // Run checks sequentially (can short-circuit on failure for 'all' strategy)
    for (const check of config.checks) {
      const result = await check.check();
      results.push(result);

      // Short-circuit for 'all' strategy if a check fails
      if (config.strategy === 'all' && !result.success) {
        break;
      }
      // Short-circuit for 'any' strategy if a check passes
      if (config.strategy === 'any' && result.success) {
        break;
      }
    }
  }

  const passed = config.strategy === 'all' ? results.every(r => r.success) : results.some(r => r.success);

  return { passed, results };
}

This function is important because it defines how Mastra Tutorial: TypeScript Framework for AI Agents and Workflows implements the patterns covered in this chapter.

How These Components Connect

flowchart TD
    A[customCheck]
    B[fileExists]
    C[fileContains]
    D[runValidation]
    E[createValidationTools]
    A --> B
    B --> C
    C --> D
    D --> E