Dry Run

Validate operations without executing

Extension URN: urn:mesh:ext:dry-run

Overview

The dry-run extension validates mutations without executing them. Useful for previewing changes, validating complex inputs, and implementing confirmation flows.

When to Use

Dry-run SHOULD be used for:

Destructive operations requiring confirmation
Complex mutations with multiple side effects
Cost estimation before execution
Input validation before submission
“What-if” analysis

Options (Request)

Field	Type	Required	Description
`enabled`	boolean	Yes	Enable dry-run mode
`include_diff`	boolean	No	Include before/after comparison
`include_side_effects`	boolean	No	List operations that would occur

Data (Response)

Field	Type	Description
`valid`	boolean	Whether operation would succeed
`would_affect`	array	Resources that would be modified
`diff`	object	Before/after state comparison
`side_effects`	array	Operations that would be triggered
`validation_errors`	array	Issues that would prevent execution
`estimated_duration`	object	Estimated execution time

Behavior

When the dry-run extension is enabled:

Server MUST validate all inputs
Server MUST NOT modify any state
Server MUST NOT trigger side effects (webhooks, notifications, etc.)
Server MUST return what would happen if executed
Server SHOULD return estimated impact

Examples

Dry-Run Request

{
  "protocol": { "name": "mesh", "version": "0.1.0" },
  "id": "req_dry",
  "call": {
    "function": "orders.bulk_cancel",
    "version": "1",
    "arguments": {
      "filter": {
        "status": "pending",
        "created_before": "2024-01-01"
      }
    }
  },
  "extensions": [
    {
      "urn": "urn:mesh:ext:dry-run",
      "options": {
        "enabled": true,
        "include_diff": true,
        "include_side_effects": true
      }
    }
  ]
}

Successful Dry-Run Response

{
  "protocol": { "name": "mesh", "version": "0.1.0" },
  "id": "req_dry",
  "result": null,
  "extensions": [
    {
      "urn": "urn:mesh:ext:dry-run",
      "data": {
        "valid": true,
        "would_affect": [
          { "type": "order", "id": "ord_001", "action": "cancel" },
          { "type": "order", "id": "ord_002", "action": "cancel" },
          { "type": "order", "id": "ord_003", "action": "cancel" }
        ],
        "diff": {
          "orders": {
            "before": { "pending": 47, "cancelled": 12 },
            "after": { "pending": 44, "cancelled": 15 }
          }
        },
        "side_effects": [
          { "type": "webhook", "event": "order.cancelled", "count": 3 },
          { "type": "email", "template": "order_cancelled", "count": 3 },
          { "type": "refund", "total": { "amount": 450.00, "currency": "USD" } }
        ],
        "estimated_duration": { "value": 2, "unit": "second" }
      }
    }
  ]
}

Invalid Dry-Run Response

{
  "protocol": { "name": "mesh", "version": "0.1.0" },
  "id": "req_dry_invalid",
  "result": null,
  "extensions": [
    {
      "urn": "urn:mesh:ext:dry-run",
      "data": {
        "valid": false,
        "validation_errors": [
          {
            "field": "filter.created_before",
            "code": "INVALID_DATE_FORMAT",
            "message": "Expected ISO 8601 date format"
          },
          {
            "field": "filter.status",
            "code": "INVALID_ENUM",
            "message": "Status 'pendng' not recognized. Did you mean 'pending'?"
          }
        ]
      }
    }
  ]
}

Delete Preview

{
  "protocol": { "name": "mesh", "version": "0.1.0" },
  "id": "req_delete_preview",
  "call": {
    "function": "users.delete",
    "version": "1",
    "arguments": { "user_id": 42 }
  },
  "extensions": [
    {
      "urn": "urn:mesh:ext:dry-run",
      "options": {
        "enabled": true,
        "include_side_effects": true
      }
    }
  ]
}

{
  "protocol": { "name": "mesh", "version": "0.1.0" },
  "id": "req_delete_preview",
  "result": null,
  "extensions": [
    {
      "urn": "urn:mesh:ext:dry-run",
      "data": {
        "valid": true,
        "would_affect": [
          { "type": "user", "id": 42, "action": "delete" },
          { "type": "order", "count": 15, "action": "anonymize" },
          { "type": "review", "count": 8, "action": "delete" },
          { "type": "session", "count": 3, "action": "invalidate" }
        ],
        "side_effects": [
          { "type": "email", "template": "account_deleted", "count": 1 },
          { "type": "webhook", "event": "user.deleted", "count": 1 },
          { "type": "audit_log", "action": "user_deletion", "count": 1 }
        ]
      }
    }
  ]
}

Notes

Dry-run responses SHOULD be deterministic for the same input
Complex operations MAY return approximations for would_affect counts
Servers MAY cache dry-run results for a short period