Execution Basics

Understanding how workflows execute in Sim is key to building efficient and reliable automations. The execution engine automatically handles dependencies, concurrency, and data flow to ensure your workflows run smoothly and predictably.

How Workflows Execute

Sim's execution engine processes workflows intelligently by analyzing dependencies and running blocks in the most efficient order possible.

Concurrent Execution by Default

Multiple blocks run concurrently when they don't depend on each other. This parallel execution dramatically improves performance without requiring manual configuration.

In this example, both the Customer Support and Deep Researcher agent blocks execute simultaneously after the Start block, maximizing efficiency.

Automatic Output Combination

When blocks have multiple dependencies, the execution engine automatically waits for all dependencies to complete, then provides their combined outputs to the next block. No manual combining required.

The Function block receives outputs from both agent blocks as soon as they complete, allowing you to process the combined results.

Smart Routing

Workflows can branch in multiple directions using routing blocks. The execution engine supports both deterministic routing (with Condition blocks) and AI-powered routing (with Router blocks).

This workflow demonstrates how execution can follow different paths based on conditions or AI decisions, with each path executing independently.

Block Types

Sim provides different types of blocks that serve specific purposes in your workflows:

All blocks execute automatically based on their dependencies - you don't need to manually manage execution order or timing.

Execution Triggers

Workflows can be triggered in several ways, depending on your use case:

Manual Testing

Click "Run" in the workflow editor to test your workflow during development. Perfect for debugging and validation.

Scheduled Execution

Set up recurring executions using cron expressions. Great for regular data processing, reports, or maintenance tasks.

API Deployment

Deploy workflows as HTTP endpoints that can be called programmatically from your applications.

Webhook Integration

Respond to events from external services like GitHub, Stripe, or custom systems in real-time.

Chat Interface

Create conversational interfaces hosted on custom subdomains for user-facing AI applications.

Execution Monitoring

When workflows run, Sim provides real-time visibility into the execution process:

• Live Block States: See which blocks are currently executing, completed, or failed
• Execution Logs: Detailed logs appear in real-time showing inputs, outputs, and any errors
• Performance Metrics: Track execution time and costs for each block
• Path Visualization: Understand which execution paths were taken through your workflow

Key Execution Principles

Understanding these core principles will help you build better workflows:

1. Dependency-Based Execution: Blocks only run when all their dependencies have completed
2. Automatic Parallelization: Independent blocks run concurrently without configuration
3. Smart Data Flow: Outputs flow automatically to connected blocks
4. Error Handling: Failed blocks stop their execution path but don't affect independent paths
5. State Persistence: All block outputs and execution details are preserved for debugging

Next Steps

Now that you understand execution basics, explore:

• Block Types - Learn about specific block capabilities
• Logging - Monitor workflow executions and debug issues
• Cost Calculation - Understand and optimize workflow costs
• Triggers - Set up different ways to run your workflows