Prerequisite Checks

When to Use This Skill

Prerequisite checks are a structured approach to fail fast validation. Instead of scattering validation throughout code, you consolidate all precondition checks into a dedicated phase that runs before any work begins.

flowchart LR
    subgraph prereq[Prerequisite Phase]
        A[Check Tools]
        B[Check Access]
        C[Check State]
        D[Check Resources]
    end

    subgraph gate[Gate]
        G{All Pass?}
    end

    subgraph exec[Execution Phase]
        E[Execute Operation]
    end

    A --> B --> C --> D --> G
    G -->|Yes| E
    G -->|No| F[Abort with Report]

    %% Ghostty Hardcore Theme
    style A fill:#65d9ef,color:#1b1d1e
    style B fill:#65d9ef,color:#1b1d1e
    style C fill:#65d9ef,color:#1b1d1e
    style D fill:#65d9ef,color:#1b1d1e
    style G fill:#fd971e,color:#1b1d1e
    style E fill:#a7e22e,color:#1b1d1e
    style F fill:#f92572,color:#1b1d1e

The key insight: check everything, then do everything.

Prerequisites

When to Apply

Decision rule: Use prerequisite checks for validation you can do upfront, not validation that requires starting the operation.

Implementation

See Implementation Patterns for:

• Check ordering strategy (cost-based)
• Implementation patterns (fail-first vs collect-all vs structured)
• Common CI/CD prerequisites checklist
• Anti-patterns to avoid

Techniques

Relationship to Other Patterns

See reference.md for additional techniques and detailed examples.

Examples

See examples.md for code examples.

Full Reference

See reference.md for complete documentation.

References

• Source Documentation
• AEL Patterns