diff --git a/internal/ai/workflow/dsl/types.go b/internal/ai/workflow/dsl/types.go
new file mode 100644
index 0000000..1812bed
--- /dev/null
+++ b/internal/ai/workflow/dsl/types.go
@@ -0,0 +1,34 @@
+package dsl
+
+import "encoding/json"
+
+type Definition struct {
+	SchemaVersion int    `json:"schemaVersion"`
+	EntryNodeID   string `json:"entryNodeId"`
+	Nodes         []Node `json:"nodes"`
+	Edges         []Edge `json:"edges"`
+}
+
+type Node struct {
+	ID       string          `json:"id"`
+	Type     string          `json:"type"`
+	Name     string          `json:"name"`
+	Position Position        `json:"position"`
+	Config   json.RawMessage `json:"config"`
+}
+
+type Position struct {
+	X float64 `json:"x"`
+	Y float64 `json:"y"`
+}
+
+type Edge struct {
+	ID        string     `json:"id"`
+	Source    string     `json:"source"`
+	Target    string     `json:"target"`
+	Condition *Condition `json:"condition,omitempty"`
+}
+
+type Condition struct {
+	Expression string `json:"expression"`
+}
diff --git a/internal/ai/workflow/registry/registry.go b/internal/ai/workflow/registry/registry.go
new file mode 100644
index 0000000..13465c7
--- /dev/null
+++ b/internal/ai/workflow/registry/registry.go
@@ -0,0 +1,33 @@
+package registry
+
+const (
+	NodeTypeStart               = "start"
+	NodeTypeKnowledgeRetrieve   = "knowledge_retrieve"
+	NodeTypeAnswerabilityGate   = "answerability_gate"
+	NodeTypeLLMReply            = "llm_reply"
+	NodeTypeCondition           = "condition"
+	NodeTypeAnalyzeConversation = "analyze_conversation"
+	NodeTypePrepareTicketDraft  = "prepare_ticket_draft"
+	NodeTypeHumanConfirm        = "human_confirm"
+	NodeTypeCreateTicket        = "create_ticket"
+	NodeTypeHandoffToHuman      = "handoff_to_human"
+	NodeTypeSendReply           = "send_reply"
+	NodeTypeEnd                 = "end"
+)
+
+func DefaultRegistry() *Registry {
+	return NewRegistry(
+		NodeSpec{Type: NodeTypeStart, Title: "Start", Description: "Conversation workflow entry.", RiskLevel: NodeRiskLevelLow},
+		NodeSpec{Type: NodeTypeKnowledgeRetrieve, Title: "Knowledge Retrieve", Description: "Retrieve knowledge for the current user message.", RiskLevel: NodeRiskLevelLow},
+		NodeSpec{Type: NodeTypeAnswerabilityGate, Title: "Answerability Gate", Description: "Decide whether retrieved knowledge is enough to answer.", RiskLevel: NodeRiskLevelLow},
+		NodeSpec{Type: NodeTypeLLMReply, Title: "LLM Reply", Description: "Generate a reply or structured analysis with the configured model.", RiskLevel: NodeRiskLevelMedium},
+		NodeSpec{Type: NodeTypeCondition, Title: "Condition", Description: "Route by controlled workflow variables.", RiskLevel: NodeRiskLevelLow},
+		NodeSpec{Type: NodeTypeAnalyzeConversation, Title: "Analyze Conversation", Description: "Analyze intent, risk, and recommended next action.", RiskLevel: NodeRiskLevelLow},
+		NodeSpec{Type: NodeTypePrepareTicketDraft, Title: "Prepare Ticket Draft", Description: "Build a ticket draft from conversation context.", RiskLevel: NodeRiskLevelMedium},
+		NodeSpec{Type: NodeTypeHumanConfirm, Title: "Human Confirm", Description: "Interrupt and wait for explicit user confirmation.", RiskLevel: NodeRiskLevelMedium, Interruptible: true},
+		NodeSpec{Type: NodeTypeCreateTicket, Title: "Create Ticket", Description: "Create a ticket from a confirmed draft.", RiskLevel: NodeRiskLevelHigh, RequiresConfirmationPredecessor: true},
+		NodeSpec{Type: NodeTypeHandoffToHuman, Title: "Handoff To Human", Description: "Transfer the conversation to human support.", RiskLevel: NodeRiskLevelHigh, RequiresConfirmationPredecessor: true},
+		NodeSpec{Type: NodeTypeSendReply, Title: "Send Reply", Description: "Return or commit customer-visible reply text.", RiskLevel: NodeRiskLevelLow},
+		NodeSpec{Type: NodeTypeEnd, Title: "End", Description: "End workflow execution.", RiskLevel: NodeRiskLevelLow},
+	)
+}
diff --git a/internal/ai/workflow/registry/spec.go b/internal/ai/workflow/registry/spec.go
new file mode 100644
index 0000000..0f98acb
--- /dev/null
+++ b/internal/ai/workflow/registry/spec.go
@@ -0,0 +1,53 @@
+package registry
+
+type NodeRiskLevel string
+
+const (
+	NodeRiskLevelLow    NodeRiskLevel = "low"
+	NodeRiskLevelMedium NodeRiskLevel = "medium"
+	NodeRiskLevelHigh   NodeRiskLevel = "high"
+)
+
+type NodeSpec struct {
+	Type                            string        `json:"type"`
+	Title                           string        `json:"title"`
+	Description                     string        `json:"description"`
+	RiskLevel                       NodeRiskLevel `json:"riskLevel"`
+	Interruptible                   bool          `json:"interruptible"`
+	RequiresConfirmationPredecessor bool          `json:"requiresConfirmationPredecessor"`
+}
+
+type Registry struct {
+	specsByType map[string]NodeSpec
+	specs       []NodeSpec
+}
+
+func NewRegistry(specs ...NodeSpec) *Registry {
+	ret := &Registry{
+		specsByType: make(map[string]NodeSpec, len(specs)),
+		specs:       make([]NodeSpec, 0, len(specs)),
+	}
+	for _, spec := range specs {
+		if spec.Type == "" {
+			continue
+		}
+		ret.specsByType[spec.Type] = spec
+		ret.specs = append(ret.specs, spec)
+	}
+	return ret
+}
+
+func (r *Registry) Get(nodeType string) (NodeSpec, bool) {
+	if r == nil {
+		return NodeSpec{}, false
+	}
+	spec, ok := r.specsByType[nodeType]
+	return spec, ok
+}
+
+func (r *Registry) List() []NodeSpec {
+	if r == nil {
+		return nil
+	}
+	return append([]NodeSpec(nil), r.specs...)
+}
diff --git a/internal/ai/workflow/validator/validator.go b/internal/ai/workflow/validator/validator.go
new file mode 100644
index 0000000..2c9e7e7
--- /dev/null
+++ b/internal/ai/workflow/validator/validator.go
@@ -0,0 +1,207 @@
+package validator
+
+import (
+	"fmt"
+	"strings"
+
+	"agent-desk/internal/ai/workflow/dsl"
+	"agent-desk/internal/ai/workflow/registry"
+)
+
+type Error struct {
+	Field   string `json:"field"`
+	Message string `json:"message"`
+}
+
+type Result struct {
+	Valid  bool    `json:"valid"`
+	Errors []Error `json:"errors"`
+}
+
+func ValidateDefinition(def dsl.Definition, reg *registry.Registry) Result {
+	if reg == nil {
+		reg = registry.DefaultRegistry()
+	}
+	v := definitionValidator{
+		def:          def,
+		registry:     reg,
+		nodesByID:    make(map[string]dsl.Node, len(def.Nodes)),
+		outgoing:     make(map[string][]string),
+		incoming:     make(map[string][]string),
+		startNodeIDs: make([]string, 0, 1),
+		endNodeIDs:   make([]string, 0, 1),
+	}
+	v.validate()
+	return Result{
+		Valid:  len(v.errors) == 0,
+		Errors: v.errors,
+	}
+}
+
+type definitionValidator struct {
+	def          dsl.Definition
+	registry     *registry.Registry
+	nodesByID    map[string]dsl.Node
+	outgoing     map[string][]string
+	incoming     map[string][]string
+	startNodeIDs []string
+	endNodeIDs   []string
+	errors       []Error
+}
+
+func (v *definitionValidator) validate() {
+	v.validateNodes()
+	v.validateEdges()
+	v.validateEntry()
+	v.validateReachability()
+	v.validateConfirmationGuards()
+}
+
+func (v *definitionValidator) validateNodes() {
+	for index, node := range v.def.Nodes {
+		node.ID = strings.TrimSpace(node.ID)
+		node.Type = strings.TrimSpace(node.Type)
+		field := fmt.Sprintf("nodes[%d]", index)
+		if node.ID == "" {
+			v.addError(field+".id", "node id is required")
+			continue
+		}
+		if _, exists := v.nodesByID[node.ID]; exists {
+			v.addError(field+".id", "duplicate node id: "+node.ID)
+			continue
+		}
+		v.nodesByID[node.ID] = node
+		if node.Type == "" {
+			v.addError(field+".type", "node type is required")
+			continue
+		}
+		if _, ok := v.registry.Get(node.Type); !ok {
+			v.addError(field+".type", "unknown node type: "+node.Type)
+			continue
+		}
+		switch node.Type {
+		case registry.NodeTypeStart:
+			v.startNodeIDs = append(v.startNodeIDs, node.ID)
+		case registry.NodeTypeEnd:
+			v.endNodeIDs = append(v.endNodeIDs, node.ID)
+		}
+	}
+	if len(v.startNodeIDs) != 1 {
+		v.addError("nodes", "workflow must contain exactly one start node")
+	}
+	if len(v.endNodeIDs) == 0 {
+		v.addError("nodes", "workflow must contain at least one end node")
+	}
+}
+
+func (v *definitionValidator) validateEdges() {
+	seen := make(map[string]struct{}, len(v.def.Edges))
+	for index, edge := range v.def.Edges {
+		edge.ID = strings.TrimSpace(edge.ID)
+		edge.Source = strings.TrimSpace(edge.Source)
+		edge.Target = strings.TrimSpace(edge.Target)
+		field := fmt.Sprintf("edges[%d]", index)
+		if edge.ID == "" {
+			v.addError(field+".id", "edge id is required")
+		} else if _, exists := seen[edge.ID]; exists {
+			v.addError(field+".id", "duplicate edge id: "+edge.ID)
+		}
+		seen[edge.ID] = struct{}{}
+		if edge.Source == "" {
+			v.addError(field+".source", "edge source is required")
+		} else if _, ok := v.nodesByID[edge.Source]; !ok {
+			v.addError(field+".source", "edge source node does not exist: "+edge.Source)
+		}
+		if edge.Target == "" {
+			v.addError(field+".target", "edge target is required")
+		} else if _, ok := v.nodesByID[edge.Target]; !ok {
+			v.addError(field+".target", "edge target node does not exist: "+edge.Target)
+		}
+		if edge.Source != "" && edge.Target != "" {
+			v.outgoing[edge.Source] = append(v.outgoing[edge.Source], edge.Target)
+			v.incoming[edge.Target] = append(v.incoming[edge.Target], edge.Source)
+		}
+	}
+}
+
+func (v *definitionValidator) validateEntry() {
+	entryNodeID := strings.TrimSpace(v.def.EntryNodeID)
+	if entryNodeID == "" {
+		v.addError("entryNodeId", "entry node id is required")
+		return
+	}
+	entry, ok := v.nodesByID[entryNodeID]
+	if !ok {
+		v.addError("entryNodeId", "entry node does not exist: "+entryNodeID)
+		return
+	}
+	if entry.Type != registry.NodeTypeStart {
+		v.addError("entryNodeId", "entry node must be the start node")
+	}
+}
+
+func (v *definitionValidator) validateReachability() {
+	entryNodeID := strings.TrimSpace(v.def.EntryNodeID)
+	if entryNodeID == "" {
+		return
+	}
+	if _, ok := v.nodesByID[entryNodeID]; !ok {
+		return
+	}
+	reachable := make(map[string]struct{}, len(v.nodesByID))
+	queue := []string{entryNodeID}
+	for len(queue) > 0 {
+		current := queue[0]
+		queue = queue[1:]
+		if _, exists := reachable[current]; exists {
+			continue
+		}
+		reachable[current] = struct{}{}
+		for _, target := range v.outgoing[current] {
+			if _, exists := reachable[target]; !exists {
+				queue = append(queue, target)
+			}
+		}
+	}
+	for id := range v.nodesByID {
+		if _, ok := reachable[id]; !ok {
+			v.addError("nodes", "node is not reachable from entry node: "+id)
+		}
+	}
+}
+
+func (v *definitionValidator) validateConfirmationGuards() {
+	for id, node := range v.nodesByID {
+		spec, ok := v.registry.Get(node.Type)
+		if !ok || !spec.RequiresConfirmationPredecessor {
+			continue
+		}
+		if !v.hasConfirmationPredecessor(id, make(map[string]struct{})) {
+			v.addError("nodes."+id, node.Type+" requires human_confirm before execution")
+		}
+	}
+}
+
+func (v *definitionValidator) hasConfirmationPredecessor(nodeID string, visiting map[string]struct{}) bool {
+	if _, seen := visiting[nodeID]; seen {
+		return false
+	}
+	visiting[nodeID] = struct{}{}
+	for _, source := range v.incoming[nodeID] {
+		node, ok := v.nodesByID[source]
+		if !ok {
+			continue
+		}
+		if node.Type == registry.NodeTypeHumanConfirm {
+			return true
+		}
+		if v.hasConfirmationPredecessor(source, visiting) {
+			return true
+		}
+	}
+	return false
+}
+
+func (v *definitionValidator) addError(field string, message string) {
+	v.errors = append(v.errors, Error{Field: field, Message: message})
+}
diff --git a/internal/ai/workflow/validator/validator_test.go b/internal/ai/workflow/validator/validator_test.go
new file mode 100644
index 0000000..065674f
--- /dev/null
+++ b/internal/ai/workflow/validator/validator_test.go
@@ -0,0 +1,129 @@
+package validator_test
+
+import (
+	"encoding/json"
+	"strings"
+	"testing"
+
+	"agent-desk/internal/ai/workflow/dsl"
+	"agent-desk/internal/ai/workflow/registry"
+	"agent-desk/internal/ai/workflow/validator"
+)
+
+func TestValidateDefinitionAcceptsMinimalConversationFlow(t *testing.T) {
+	result := validator.ValidateDefinition(minimalDefinition(), registry.DefaultRegistry())
+
+	if !result.Valid {
+		t.Fatalf("expected valid definition, got errors: %#v", result.Errors)
+	}
+}
+
+func TestValidateDefinitionRejectsMissingStart(t *testing.T) {
+	def := minimalDefinition()
+	def.Nodes = []dsl.Node{
+		{ID: "reply_1", Type: "send_reply", Config: json.RawMessage(`{"text":"hello"}`)},
+		{ID: "end_1", Type: "end"},
+	}
+
+	result := validator.ValidateDefinition(def, registry.DefaultRegistry())
+
+	if result.Valid {
+		t.Fatalf("expected missing start to be invalid")
+	}
+	if !hasValidationMessage(result, "exactly one start node") {
+		t.Fatalf("expected start error, got %#v", result.Errors)
+	}
+}
+
+func TestValidateDefinitionRejectsUnknownNodeType(t *testing.T) {
+	def := minimalDefinition()
+	def.Nodes = append(def.Nodes, dsl.Node{ID: "unknown_1", Type: "unknown_node"})
+	def.Edges = append(def.Edges, dsl.Edge{ID: "e3", Source: "reply_1", Target: "unknown_1"})
+
+	result := validator.ValidateDefinition(def, registry.DefaultRegistry())
+
+	if result.Valid {
+		t.Fatalf("expected unknown node type to be invalid")
+	}
+	if !hasValidationMessage(result, "unknown node type") {
+		t.Fatalf("expected unknown-node error, got %#v", result.Errors)
+	}
+}
+
+func TestValidateDefinitionRejectsUnguardedCreateTicket(t *testing.T) {
+	def := dsl.Definition{
+		SchemaVersion: 1,
+		EntryNodeID:   "start_1",
+		Nodes: []dsl.Node{
+			{ID: "start_1", Type: "start"},
+			{ID: "draft_1", Type: "prepare_ticket_draft"},
+			{ID: "create_1", Type: "create_ticket"},
+			{ID: "end_1", Type: "end"},
+		},
+		Edges: []dsl.Edge{
+			{ID: "e1", Source: "start_1", Target: "draft_1"},
+			{ID: "e2", Source: "draft_1", Target: "create_1"},
+			{ID: "e3", Source: "create_1", Target: "end_1"},
+		},
+	}
+
+	result := validator.ValidateDefinition(def, registry.DefaultRegistry())
+
+	if result.Valid {
+		t.Fatalf("expected unguarded create_ticket to be invalid")
+	}
+	if !hasValidationMessage(result, "requires human_confirm") {
+		t.Fatalf("expected confirmation guard error, got %#v", result.Errors)
+	}
+}
+
+func TestValidateDefinitionAcceptsConfirmedCreateTicket(t *testing.T) {
+	def := dsl.Definition{
+		SchemaVersion: 1,
+		EntryNodeID:   "start_1",
+		Nodes: []dsl.Node{
+			{ID: "start_1", Type: "start"},
+			{ID: "draft_1", Type: "prepare_ticket_draft"},
+			{ID: "confirm_1", Type: "human_confirm"},
+			{ID: "create_1", Type: "create_ticket"},
+			{ID: "end_1", Type: "end"},
+		},
+		Edges: []dsl.Edge{
+			{ID: "e1", Source: "start_1", Target: "draft_1"},
+			{ID: "e2", Source: "draft_1", Target: "confirm_1"},
+			{ID: "e3", Source: "confirm_1", Target: "create_1"},
+			{ID: "e4", Source: "create_1", Target: "end_1"},
+		},
+	}
+
+	result := validator.ValidateDefinition(def, registry.DefaultRegistry())
+
+	if !result.Valid {
+		t.Fatalf("expected confirmed create_ticket to be valid, got %#v", result.Errors)
+	}
+}
+
+func minimalDefinition() dsl.Definition {
+	return dsl.Definition{
+		SchemaVersion: 1,
+		EntryNodeID:   "start_1",
+		Nodes: []dsl.Node{
+			{ID: "start_1", Type: "start"},
+			{ID: "reply_1", Type: "send_reply", Config: json.RawMessage(`{"text":"hello"}`)},
+			{ID: "end_1", Type: "end"},
+		},
+		Edges: []dsl.Edge{
+			{ID: "e1", Source: "start_1", Target: "reply_1"},
+			{ID: "e2", Source: "reply_1", Target: "end_1"},
+		},
+	}
+}
+
+func hasValidationMessage(result validator.Result, want string) bool {
+	for _, item := range result.Errors {
+		if strings.Contains(item.Message, want) {
+			return true
+		}
+	}
+	return false
+}