diff --git a/pkg/model/provider/gemini/client.go b/pkg/model/provider/gemini/client.go
index e1747a0826..e22336826d 100644
--- a/pkg/model/provider/gemini/client.go
+++ b/pkg/model/provider/gemini/client.go
@@ -563,6 +563,7 @@ func ConvertParametersToSchema(params any) (*genai.Schema, error) {
 		return nil, err
 	}
 
+	normalizeBooleanSchemas(m)
 	normalizeTypeFields(m)
 	normalizeEnumValues(m)
 
@@ -574,6 +575,60 @@ func ConvertParametersToSchema(params any) (*genai.Schema, error) {
 	return schema, nil
 }
 
+// normalizeBooleanSchemas recursively replaces JSON Schema boolean sub-schemas
+// with their object-form equivalent. JSON Schema (draft 2020-12) allows any
+// sub-schema position — a "properties" value, "items", an "anyOf" entry, etc. —
+// to be a bare boolean: true means "any value validates", false means "nothing
+// validates". Gemini's Schema type (an OpenAPI 3.0 subset) has no such form:
+// genai unmarshals every sub-schema into a *genai.Schema object and hard-fails
+// on a JSON boolean ("cannot unmarshal bool into Go struct field
+// Schema.properties of type genai.Schema").
+//
+// A Go any/interface{} field in an MCP tool's input struct is the common source.
+// Schema generators such as google/jsonschema-go render an unconstrained field
+// as the boolean `true` schema, so any MCP server exposing such a tool would
+// otherwise be unusable with Gemini. Coercing `true` to an empty object schema
+// {} preserves "any value" while staying parseable by Gemini. additionalProperties
+// booleans are left untouched — genai has no such field and ignores the keyword.
+func normalizeBooleanSchemas(m map[string]any) {
+	// Keywords whose value is a map of sub-schemas.
+	for _, key := range []string{"properties", "patternProperties", "$defs", "definitions"} {
+		if sub, ok := m[key].(map[string]any); ok {
+			for name, v := range sub {
+				sub[name] = coerceBooleanSchema(v)
+			}
+		}
+	}
+	// Keywords whose value is a list of sub-schemas.
+	for _, key := range []string{"allOf", "anyOf", "oneOf", "prefixItems"} {
+		if arr, ok := m[key].([]any); ok {
+			for i, v := range arr {
+				arr[i] = coerceBooleanSchema(v)
+			}
+		}
+	}
+	// Keywords whose value is a single sub-schema.
+	for _, key := range []string{"items", "not", "if", "then", "else", "contains", "propertyNames"} {
+		if v, ok := m[key]; ok {
+			m[key] = coerceBooleanSchema(v)
+		}
+	}
+}
+
+// coerceBooleanSchema turns a boolean JSON-Schema node into an empty object
+// schema ({}) and recurses into object nodes. A `false` schema (nothing
+// validates) has no Gemini equivalent and is not meaningful for a tool input
+// parameter, so it is also mapped to {} rather than dropped.
+func coerceBooleanSchema(v any) any {
+	if _, ok := v.(bool); ok {
+		return map[string]any{}
+	}
+	if sub, ok := v.(map[string]any); ok {
+		normalizeBooleanSchemas(sub)
+	}
+	return v
+}
+
 // normalizeTypeFields recursively converts type arrays to single string values.
 // JSON Schema allows "type": ["string", "null"] but Gemini expects a single type.
 // This picks the first non-null type from arrays.
diff --git a/pkg/model/provider/gemini/schema_boolean_test.go b/pkg/model/provider/gemini/schema_boolean_test.go
new file mode 100644
index 0000000000..d1875d5949
--- /dev/null
+++ b/pkg/model/provider/gemini/schema_boolean_test.go
@@ -0,0 +1,77 @@
+package gemini
+
+import (
+	"testing"
+)
+
+// A tool input schema containing a boolean sub-schema — the shape a JSON Schema
+// generator emits for a Go any/interface{} field — must convert without error.
+// Before normalizeBooleanSchemas this failed with
+// "cannot unmarshal bool into Go struct field Schema.properties of type genai.Schema".
+func TestConvertParametersToSchema_BooleanSubSchema(t *testing.T) {
+	params := map[string]any{
+		"type": "object",
+		"properties": map[string]any{
+			"address": map[string]any{"type": "string"},
+			// interface{} fields -> boolean "true" schema (any value).
+			"count":    true,
+			"for_each": true,
+			"nested": map[string]any{
+				"type": "array",
+				"items": map[string]any{
+					"type": "object",
+					"properties": map[string]any{
+						"value": true, // any value
+					},
+				},
+			},
+		},
+		"required": []any{"address"},
+	}
+
+	schema, err := ConvertParametersToSchema(params)
+	if err != nil {
+		t.Fatalf("ConvertParametersToSchema: %v", err)
+	}
+	if schema == nil {
+		t.Fatal("nil schema")
+	}
+	if _, ok := schema.Properties["count"]; !ok {
+		t.Errorf("count property dropped; got %v", schema.Properties)
+	}
+	if _, ok := schema.Properties["nested"]; !ok {
+		t.Errorf("nested property dropped; got %v", schema.Properties)
+	}
+}
+
+func TestNormalizeBooleanSchemas(t *testing.T) {
+	m := map[string]any{
+		"properties": map[string]any{
+			"any":  true,
+			"none": false,
+			"obj": map[string]any{
+				"type":  "array",
+				"items": true,
+			},
+		},
+		// additionalProperties booleans must be preserved: genai ignores the
+		// keyword, and false carries meaning for other clients.
+		"additionalProperties": false,
+	}
+	normalizeBooleanSchemas(m)
+
+	props := m["properties"].(map[string]any)
+	if _, ok := props["any"].(map[string]any); !ok {
+		t.Errorf("true schema not coerced to object: %T", props["any"])
+	}
+	if _, ok := props["none"].(map[string]any); !ok {
+		t.Errorf("false schema not coerced to object: %T", props["none"])
+	}
+	obj := props["obj"].(map[string]any)
+	if _, ok := obj["items"].(map[string]any); !ok {
+		t.Errorf("items true schema not coerced: %T", obj["items"])
+	}
+	if m["additionalProperties"] != false {
+		t.Errorf("additionalProperties changed: %v", m["additionalProperties"])
+	}
+}