Custom Engines

Custom Engines

Define custom GitHub Actions steps without AI interpretation for deterministic workflows.

engine: custom

Extended configuration:

engine:
  id: custom
  steps:
    - name: Install dependencies
      run: npm ci

Custom Engine Error Patterns

All engines (Copilot, Claude, Codex, and Custom) support custom error pattern recognition for enhanced log validation. This allows you to define project-specific error formats that should be detected in agent logs.

Basic Usage

engine:
  id: copilot
  error_patterns:
    - pattern: "\\[(\\d{4}-\\d{2}-\\d{2}T\\d{2}:\\d{2}:\\d{2})\\]\\s+(ERROR):\\s+(.+)"
      level_group: 2
      message_group: 3
      description: "Custom error format with timestamp"

Multiple Patterns

Define multiple error patterns to catch different error formats:

engine:
  id: claude
  error_patterns:
    - pattern: "PROJECT_ERROR:\\s+(.+)"
      message_group: 1
      description: "Project-specific error"
    - pattern: "VALIDATION_FAILED:\\s+(.+)"
      message_group: 1
      description: "Validation error"

Pattern Fields

• pattern (required): ECMAScript regular expression to match log lines
• level_group (optional): Capture group index (1-based) containing error level (ERROR, WARNING, etc.). Use 0 to infer from pattern content.
• message_group (optional): Capture group index (1-based) containing the error message. Use 0 to use the entire match.
• description (optional): Human-readable description of what this pattern matches

Shared Error Patterns

Error patterns can be defined in shared workflows and imported:

shared/error-patterns.md:

---
engine:
  error_patterns:
    - pattern: "SHARED_ERROR:\\s+(.+)"
      message_group: 1
      description: "Shared error pattern"
---

Main workflow:

---
imports:
  - ./shared/error-patterns.md
engine: copilot
---

Custom error patterns are merged with engine-specific built-in patterns during workflow compilation.

Related Documentation

• AI Engines - Complete guide to AI engines
• Frontmatter - Complete configuration reference
• Tools - Available tools and MCP servers