diff --git a/registry/validate.go b/registry/validate.go
new file mode 100644
index 00000000..4d1b5e57
--- /dev/null
+++ b/registry/validate.go
@@ -0,0 +1,167 @@
+package registry
+
+import (
+	"fmt"
+	"strings"
+)
+
+// ValidationError represents one or more integrity violations.
+type ValidationError struct {
+	ID     string
+	Errors []string
+}
+
+func (v *ValidationError) Error() string {
+	return fmt.Sprintf("%s: %s", v.ID, strings.Join(v.Errors, "; "))
+}
+
+// ValidateFunction checks integrity rules from docs/integrity.md.
+// knownFunctions and knownTypes are sets of IDs that exist in the registry
+// (including the current indexing batch).
+func ValidateFunction(f *Function, knownFunctions, knownTypes map[string]bool) *ValidationError {
+	var errs []string
+
+	// Required fields
+	if f.Name == "" {
+		errs = append(errs, "name is required")
+	}
+	if f.Kind == "" {
+		errs = append(errs, "kind is required")
+	}
+	if f.Lang == "" {
+		errs = append(errs, "lang is required")
+	}
+	if f.Domain == "" {
+		errs = append(errs, "domain is required")
+	}
+	if f.Description == "" {
+		errs = append(errs, "description is required")
+	}
+
+	// Pipeline rules
+	if f.Kind == KindPipeline {
+		if f.Purity != PurityImpure {
+			errs = append(errs, "pipeline must be impure")
+		}
+		if len(f.UsesFunctions) == 0 {
+			errs = append(errs, "pipeline uses_functions cannot be empty")
+		}
+	}
+
+	// Purity rules
+	if f.Purity == PurityPure {
+		if f.ReturnsOptional {
+			errs = append(errs, "pure function cannot have returns_optional: true (model as sum type)")
+		}
+		if f.ErrorType != "" {
+			errs = append(errs, "pure function cannot have error_type")
+		}
+	}
+	if f.Purity == PurityImpure && f.Kind != KindComponent {
+		if f.ErrorType == "" {
+			errs = append(errs, "impure function must declare error_type")
+		}
+	}
+
+	// Tested rules
+	if f.Tested {
+		if f.TestFilePath == "" {
+			errs = append(errs, "tested: true requires test_file_path")
+		}
+		if len(f.Tests) == 0 {
+			errs = append(errs, "tested: true requires non-empty tests")
+		}
+	} else {
+		if len(f.Tests) > 0 {
+			errs = append(errs, "tested: false but tests is not empty")
+		}
+		if f.TestFilePath != "" {
+			errs = append(errs, "tested: false but test_file_path is set")
+		}
+	}
+
+	// Component rules
+	if f.Kind == KindComponent {
+		if f.Framework == "" {
+			errs = append(errs, "component must declare framework")
+		}
+		if len(f.Returns) > 0 {
+			errs = append(errs, "component returns must be empty (use emits)")
+		}
+		if f.HasState != nil && *f.HasState && f.Purity != PurityImpure {
+			errs = append(errs, "component with has_state: true must be impure")
+		}
+	}
+
+	// File path must be relative
+	if f.FilePath != "" && strings.HasPrefix(f.FilePath, "/") {
+		errs = append(errs, "file_path must be relative to registry root")
+	}
+
+	// Reference validation
+	for _, ref := range f.UsesFunctions {
+		if !knownFunctions[ref] {
+			errs = append(errs, fmt.Sprintf("uses_functions references unknown function: %s", ref))
+		}
+	}
+	for _, ref := range f.UsesTypes {
+		if !knownTypes[ref] {
+			errs = append(errs, fmt.Sprintf("uses_types references unknown type: %s", ref))
+		}
+	}
+	for _, ref := range f.Returns {
+		if !knownTypes[ref] {
+			errs = append(errs, fmt.Sprintf("returns references unknown type: %s", ref))
+		}
+	}
+	if f.ErrorType != "" {
+		if !knownTypes[f.ErrorType] {
+			errs = append(errs, fmt.Sprintf("error_type references unknown type: %s", f.ErrorType))
+		}
+	}
+
+	if len(errs) > 0 {
+		return &ValidationError{ID: f.ID, Errors: errs}
+	}
+	return nil
+}
+
+// ValidateType checks integrity rules for types.
+func ValidateType(t *Type, knownTypes map[string]bool) *ValidationError {
+	var errs []string
+
+	if t.Name == "" {
+		errs = append(errs, "name is required")
+	}
+	if t.Lang == "" {
+		errs = append(errs, "lang is required")
+	}
+	if t.Domain == "" {
+		errs = append(errs, "domain is required")
+	}
+	if t.Description == "" {
+		errs = append(errs, "description is required")
+	}
+	if t.Algebraic != AlgebraicProduct && t.Algebraic != AlgebraicSum {
+		errs = append(errs, fmt.Sprintf("algebraic must be 'product' or 'sum', got %q", t.Algebraic))
+	}
+
+	if t.FilePath != "" && strings.HasPrefix(t.FilePath, "/") {
+		errs = append(errs, "file_path must be relative to registry root")
+	}
+
+	// Self-reference check
+	for _, ref := range t.UsesTypes {
+		if ref == t.ID {
+			errs = append(errs, "type cannot reference itself in uses_types")
+		}
+		if !knownTypes[ref] {
+			errs = append(errs, fmt.Sprintf("uses_types references unknown type: %s", ref))
+		}
+	}
+
+	if len(errs) > 0 {
+		return &ValidationError{ID: t.ID, Errors: errs}
+	}
+	return nil
+}