Pre-Execution Validation

The kubernetes-mcp-server includes a validation layer that catches errors before they reach the Kubernetes API. This prevents AI hallucinations (like typos in resource names) and permission issues from causing confusing failures.

Why Validation?

When an AI assistant makes a Kubernetes API call with errors, the raw Kubernetes error messages can be cryptic:

the server doesn't have a resource type "Deploymnt"

With validation enabled, you get clearer feedback:

Validation Error [RESOURCE_NOT_FOUND]: Resource deploymnt does not exist in the cluster

The validation layer catches these types of issues:

1. Resource Existence - Catches typos like "Deploymnt" instead of "Deployment" (checked in access control)
2. Schema Validation - Catches invalid fields like "spec.replcias" instead of "spec.replicas"
3. RBAC Validation - Pre-checks permissions before attempting operations

Configuration

Validation is disabled by default. Schema and RBAC validators run together when enabled. Resource existence is always checked as part of access control.

# Enable all validation (default: false)
validation_enabled = true

Configuration Reference

TOML Field	Default	Description
validation_enabled	false	Enable/disable all validators

Note: The schema validator caches the OpenAPI schema for 15 minutes internally.

How It Works

Validation Flow

Validation happens at the HTTP RoundTripper level, intercepting all Kubernetes API calls:

MCP Tool Call → Kubernetes Client → HTTP RoundTripper → Kubernetes API
                                          ↓
                                   Access Control
                                   - Check deny list
                                   - Check resource exists
                                          ↓
                                   Schema Validator (if enabled)
                                   "Are the fields valid?"
                                          ↓
                                   RBAC Validator (if enabled)
                                   "Does the user have permission?"
                                          ↓
                                   Forward to K8s API

This HTTP-layer approach ensures all Kubernetes API calls are validated, including those from plugins (KubeVirt, Kiali, Helm, etc.) - not just the core tools.

If any validator fails, the request is rejected with a clear error message before reaching the Kubernetes API.

1. Resource Existence (Access Control)

The access control layer validates that the requested resource type exists in the cluster. This check runs regardless of whether validation is enabled.

What it catches:

• Typos in Kind names: "Deploymnt" → should be "Deployment"
• Wrong API versions: "apps/v2" → should be "apps/v1"
• Non-existent custom resources

Example error:

Validation Error [RESOURCE_NOT_FOUND]: Resource deploymnt.apps does not exist in the cluster

2. Schema Validation

Validates resource manifests against the cluster's OpenAPI schema for create/update operations.

What it catches:

• Invalid field names: "spec.replcias" → should be "spec.replicas"
• Wrong field types: string where integer expected
• Missing required fields

Example error:

Validation Error [INVALID_FIELD]: unknown field "spec.replcias"

Note: Schema validation uses kubectl's validation library and caches the OpenAPI schema for 15 minutes.

3. RBAC Validation

Pre-checks permissions using Kubernetes SelfSubjectAccessReview before attempting operations.

What it catches:

• Missing permissions: can't create Deployments in namespace X
• Cluster-scoped vs namespace-scoped mismatches
• Read-only access attempting writes

Example error:

Validation Error [PERMISSION_DENIED]: Cannot create deployments.apps in namespace "production"

Note: RBAC validation uses the same credentials as the actual operation - either the server's service account or the user's token (when OAuth is enabled).

Error Codes

Code	Description
RESOURCE_NOT_FOUND	The requested resource type doesn't exist in the cluster
INVALID_FIELD	A field in the manifest doesn't exist or has the wrong type
PERMISSION_DENIED	RBAC denies the requested operation