Output Contract Enforcer

Validates that a DAG node's output matches its declared JSON schema before passing to downstream nodes. The glue that makes multi-agent DAGs reliable. Without this, downstream nodes receive unpredictable input and the DAG breaks.

When to Use

✅ Use for:

• Validating a node's output against its declared schema

• Generating output schemas from natural-language output descriptions

• Debugging why a downstream node rejected its input

• Ensuring contract compatibility between connected nodes

❌ NOT for:

• Assessing content quality or correctness (use dag-quality )

• Grading skill quality (use skill-grader )

• General JSON schema work outside DAG context

Validation Process

flowchart TD O[Node output] --> P[Parse as JSON] P -->|Parse error| E1[FAIL: Not valid JSON] P -->|Valid JSON| S[Check against schema] S --> R{Required fields?} R -->|Missing| E2[FAIL: Missing required field X] R -->|Present| T{Type check?} T -->|Wrong type| E3[FAIL: Field X expected string, got number] T -->|Correct| C{Constraints?} C -->|Violated| E4[FAIL: Field X violates constraint Y] C -->|Met| V[PASS: Contract satisfied]

What Gets Checked

Check Example Failure Message

JSON parseable {broken json

"Output is not valid JSON"

Required fields status missing "Missing required field: status"

Field types status: 42 (expected string) "Field 'status' expected string, got number"

Enum values status: "maybe"

"Field 'status' must be one of: pass, warn, fail"

String constraints summary: "" (minLength: 1) "Field 'summary' must have minLength 1"

Number constraints score: 1.5 (maximum: 1.0) "Field 'score' must be ≤ 1.0"

Array constraints items: [] (minItems: 1) "Field 'items' must have at least 1 item"

Nested objects Missing sub-field "Field 'metadata.cost' is required"

The Standard Output Contract

Every DAG node should produce output matching this base schema (fields can be extended):

{ "type": "object", "required": ["status", "summary"], "properties": { "status": { "type": "string", "enum": ["pass", "warn", "fail"] }, "summary": { "type": "string", "minLength": 1, "description": "1-3 sentence description of what was produced" }, "artifacts": { "type": "array", "items": { "type": "string" }, "description": "List of files created or modified" }, "data": { "type": "object", "description": "Node-specific output data (schema varies per node)" }, "risks": { "type": "array", "items": { "type": "string" }, "description": "Remaining risks or assumptions" } } }

Contract Compatibility Check

When connecting Node A's output to Node B's input, verify:

• Every field B requires is present in A's output schema

• Types match (A produces string, B expects string)

• A's output constraints are compatible with B's input constraints

• If A produces optional fields that B requires → incompatible

Node A output: { status: string, recommendations: string[] } Node B input: { status: string, recommendations: string[], priority: number }

Result: INCOMPATIBLE — Node B requires 'priority' but Node A doesn't produce it. Fix: Add 'priority' to Node A's output, or add a transformer node between A and B.

Schema Generation

When a node description says "produces a list of recommendations with priorities," generate:

{ "type": "object", "required": ["status", "summary", "data"], "properties": { "status": { "type": "string", "enum": ["pass", "warn", "fail"] }, "summary": { "type": "string", "minLength": 1 }, "data": { "type": "object", "required": ["recommendations"], "properties": { "recommendations": { "type": "array", "minItems": 1, "items": { "type": "object", "required": ["text", "priority"], "properties": { "text": { "type": "string" }, "priority": { "type": "integer", "minimum": 1, "maximum": 5 } } } } } } } }

Anti-Patterns

No Contract at All

Wrong: Nodes produce free-form text with no schema. Why: Downstream nodes can't reliably parse the input. The DAG is fragile. Right: Every node declares its output schema. Every output is validated before passing downstream.

Overly Strict Contracts

Wrong: Requiring exact character counts, specific formatting, or field values that depend on runtime context. Right: Constrain structure (types, required fields), not content. Let dag-quality handle content assessment.

Ignoring Optional Fields

Wrong: Treating all fields as required. Right: Use required only for fields that downstream nodes absolutely need. Mark everything else as optional.