diff --git a/CHANGELOG.md b/CHANGELOG.md
index a740d3a..7d785c4 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,9 @@
 ## Unreleased
 
+### Dependencies
+
+- **Upgrade `zod` from `^3.25.42` to `^4.3.6`** — migrated all `z.record()` calls to require explicit key schema (`z.string()`), updated test assertions for changed error message format
+
 ## 0.6.0 - 2026-04-01
 
 ### Security
diff --git a/package-lock.json b/package-lock.json
index 83d4acf..bc9c6df 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -21,7 +21,7 @@
         "@opentelemetry/sdk-node": "^0.56.0",
         "@opentelemetry/sdk-trace-base": "^1.30.1",
         "@opentelemetry/semantic-conventions": "^1.30.1",
-        "zod": "^3.25.42"
+        "zod": "^4.3.6"
       },
       "bin": {
         "mapbox-mcp-devkit": "dist/esm/index.js"
@@ -13854,7 +13854,9 @@
       }
     },
     "node_modules/zod": {
-      "version": "3.25.71",
+      "version": "4.3.6",
+      "resolved": "https://registry.npmjs.org/zod/-/zod-4.3.6.tgz",
+      "integrity": "sha512-rftlrkhHZOcjDwkGlnUtZZkvaPHCsDATp4pGpuOOMDaTdDDXF91wuVDJoWoPsKX/3YPQ5fHuF3STjcYyKr+Qhg==",
       "license": "MIT",
       "funding": {
         "url": "https://github.com/sponsors/colinhacks"
diff --git a/package.json b/package.json
index 1732dc7..f9c5e96 100644
--- a/package.json
+++ b/package.json
@@ -60,7 +60,7 @@
     "@opentelemetry/sdk-node": "^0.56.0",
     "@opentelemetry/sdk-trace-base": "^1.30.1",
     "@opentelemetry/semantic-conventions": "^1.30.1",
-    "zod": "^3.25.42"
+    "zod": "^4.3.6"
   },
   "devDependencies": {
     "@eslint/js": "^9.27.0",
diff --git a/src/schemas/style.ts b/src/schemas/style.ts
index 88fcb0e..bd936a2 100644
--- a/src/schemas/style.ts
+++ b/src/schemas/style.ts
@@ -28,7 +28,7 @@ const LightsSchema = z.array(
   z.object({
     id: z.string(),
     type: z.enum(['ambient', 'directional']),
-    properties: z.record(z.any()).optional()
+    properties: z.record(z.string(), z.any()).optional()
   })
 );
 
@@ -48,7 +48,7 @@ const VectorSourceSchema = z.object({
   minzoom: z.number().min(0).max(22).optional(),
   maxzoom: z.number().min(0).max(22).optional(),
   attribution: z.string().optional(),
-  promoteId: z.union([z.string(), z.record(z.string())]).optional(),
+  promoteId: z.union([z.string(), z.record(z.string(), z.string())]).optional(),
   volatile: z.boolean().optional()
 });
 
@@ -88,10 +88,10 @@ const GeoJSONSourceSchema = z.object({
   cluster: z.boolean().optional(),
   clusterRadius: z.number().optional(),
   clusterMaxZoom: z.number().optional(),
-  clusterProperties: z.record(z.any()).optional(),
+  clusterProperties: z.record(z.string(), z.any()).optional(),
   lineMetrics: z.boolean().optional(),
   generateId: z.boolean().optional(),
-  promoteId: z.union([z.string(), z.record(z.string())]).optional()
+  promoteId: z.union([z.string(), z.record(z.string(), z.string())]).optional()
 });
 
 const ImageSourceSchema = z.object({
@@ -156,9 +156,9 @@ const LayerSchema = z.object({
   minzoom: z.number().min(0).max(24).optional(),
   maxzoom: z.number().min(0).max(24).optional(),
   filter: z.any().optional().describe('Expression for filtering features'),
-  layout: z.record(z.any()).optional(),
-  paint: z.record(z.any()).optional(),
-  metadata: z.record(z.any()).optional(),
+  layout: z.record(z.string(), z.any()).optional(),
+  paint: z.record(z.string(), z.any()).optional(),
+  metadata: z.record(z.string(), z.any()).optional(),
   slot: z.string().optional().describe('Slot this layer is assigned to')
 });
 
@@ -166,7 +166,7 @@ const LayerSchema = z.object({
 const StyleImportSchema = z.object({
   id: z.string(),
   url: z.string(),
-  config: z.record(z.any()).optional()
+  config: z.record(z.string(), z.any()).optional()
 });
 
 // Base Style properties (shared between input and output)
@@ -175,12 +175,14 @@ export const BaseStylePropertiesSchema = z.object({
   version: z
     .literal(8)
     .describe('Style specification version number. Must be 8'),
-  sources: z.record(SourceSchema).describe('Data source specifications'),
+  sources: z
+    .record(z.string(), SourceSchema)
+    .describe('Data source specifications'),
   layers: z.array(LayerSchema).describe('Layers in draw order'),
 
   // Optional Style Spec properties
   metadata: z
-    .record(z.any())
+    .record(z.string(), z.any())
     .optional()
     .describe('Arbitrary properties for tracking'),
   center: CoordinatesSchema.optional().describe(
@@ -203,9 +205,13 @@ export const BaseStylePropertiesSchema = z.object({
   terrain: TerrainSchema.optional()
     .nullable()
     .describe('Global terrain elevation'),
-  fog: z.record(z.any()).optional().nullable().describe('Fog properties'),
+  fog: z
+    .record(z.string(), z.any())
+    .optional()
+    .nullable()
+    .describe('Fog properties'),
   projection: z
-    .record(z.any())
+    .record(z.string(), z.any())
     .optional()
     .nullable()
     .describe('Map projection'),
diff --git a/src/tools/compare-styles-tool/CompareStylesTool.input.schema.ts b/src/tools/compare-styles-tool/CompareStylesTool.input.schema.ts
index 673b9cf..0ea7d15 100644
--- a/src/tools/compare-styles-tool/CompareStylesTool.input.schema.ts
+++ b/src/tools/compare-styles-tool/CompareStylesTool.input.schema.ts
@@ -5,10 +5,10 @@ import { z } from 'zod';
 
 export const CompareStylesInputSchema = z.object({
   styleA: z
-    .union([z.string(), z.record(z.unknown())])
+    .union([z.string(), z.record(z.string(), z.unknown())])
     .describe('First Mapbox style (JSON string or style object)'),
   styleB: z
-    .union([z.string(), z.record(z.unknown())])
+    .union([z.string(), z.record(z.string(), z.unknown())])
     .describe('Second Mapbox style (JSON string or style object)'),
   ignoreMetadata: z
     .boolean()
diff --git a/src/tools/create-style-tool/CreateStyleTool.input.schema.ts b/src/tools/create-style-tool/CreateStyleTool.input.schema.ts
index a20c5f2..ba7f950 100644
--- a/src/tools/create-style-tool/CreateStyleTool.input.schema.ts
+++ b/src/tools/create-style-tool/CreateStyleTool.input.schema.ts
@@ -9,7 +9,7 @@ import { z } from 'zod';
 export const CreateStyleInputSchema = z.object({
   name: z.string().describe('Human-readable name for the style'),
   style: z
-    .record(z.any())
+    .record(z.string(), z.any())
     .describe(
       'Complete Mapbox Style Specification object. Must include: version (8), sources, layers. Optional: sprite, glyphs, center, zoom, bearing, pitch, metadata, etc. See https://docs.mapbox.com/mapbox-gl-js/style-spec/'
     )
diff --git a/src/tools/list-styles-tool/ListStylesTool.output.schema.ts b/src/tools/list-styles-tool/ListStylesTool.output.schema.ts
index 3c73b6d..296cd42 100644
--- a/src/tools/list-styles-tool/ListStylesTool.output.schema.ts
+++ b/src/tools/list-styles-tool/ListStylesTool.output.schema.ts
@@ -30,7 +30,10 @@ const StyleMetadataSchema = z.object({
   pitch: z.number().optional().describe('Default pitch in degrees'),
 
   // Sources and layers may or may not be included in list responses
-  sources: z.record(z.any()).optional().describe('Style data sources'),
+  sources: z
+    .record(z.string(), z.any())
+    .optional()
+    .describe('Style data sources'),
   layers: z.array(z.any()).optional().describe('Style layers'),
 
   // Additional metadata fields
diff --git a/src/tools/optimize-style-tool/OptimizeStyleTool.input.schema.ts b/src/tools/optimize-style-tool/OptimizeStyleTool.input.schema.ts
index e9271ed..a385c80 100644
--- a/src/tools/optimize-style-tool/OptimizeStyleTool.input.schema.ts
+++ b/src/tools/optimize-style-tool/OptimizeStyleTool.input.schema.ts
@@ -5,7 +5,7 @@ import { z } from 'zod';
 
 export const OptimizeStyleInputSchema = z.object({
   style: z
-    .union([z.string(), z.record(z.unknown())])
+    .union([z.string(), z.record(z.string(), z.unknown())])
     .describe('Mapbox style to optimize (JSON string or style object)'),
   optimizations: z
     .array(
diff --git a/src/tools/optimize-style-tool/OptimizeStyleTool.output.schema.ts b/src/tools/optimize-style-tool/OptimizeStyleTool.output.schema.ts
index 7142f29..f31cbf9 100644
--- a/src/tools/optimize-style-tool/OptimizeStyleTool.output.schema.ts
+++ b/src/tools/optimize-style-tool/OptimizeStyleTool.output.schema.ts
@@ -10,7 +10,9 @@ const OptimizationSchema = z.object({
 });
 
 export const OptimizeStyleOutputSchema = z.object({
-  optimizedStyle: z.record(z.unknown()).describe('The optimized Mapbox style'),
+  optimizedStyle: z
+    .record(z.string(), z.unknown())
+    .describe('The optimized Mapbox style'),
   optimizations: z
     .array(OptimizationSchema)
     .describe('List of optimizations that were applied'),
diff --git a/src/tools/style-builder-tool/StyleBuilderTool.input.schema.ts b/src/tools/style-builder-tool/StyleBuilderTool.input.schema.ts
index 0d34073..a365dca 100644
--- a/src/tools/style-builder-tool/StyleBuilderTool.input.schema.ts
+++ b/src/tools/style-builder-tool/StyleBuilderTool.input.schema.ts
@@ -52,7 +52,7 @@ const LayerConfigSchema = z.object({
       z.number(),
       z.boolean(),
       z.array(z.unknown()),
-      z.record(z.unknown())
+      z.record(z.string(), z.unknown())
     ])
     .optional()
     .describe('Custom filter expression'),
@@ -109,7 +109,7 @@ const LayerConfigSchema = z.object({
       z.number(),
       z.boolean(),
       z.array(z.unknown()),
-      z.record(z.unknown())
+      z.record(z.string(), z.unknown())
     ])
     .optional()
     .describe('Custom Mapbox expression for advanced styling'),
diff --git a/src/tools/tilequery-tool/TilequeryTool.output.schema.ts b/src/tools/tilequery-tool/TilequeryTool.output.schema.ts
index e46923e..4c99b62 100644
--- a/src/tools/tilequery-tool/TilequeryTool.output.schema.ts
+++ b/src/tools/tilequery-tool/TilequeryTool.output.schema.ts
@@ -32,7 +32,7 @@ const VectorTilequeryFeatureSchema = z.object({
           .describe('The vector tile layer of the feature result')
       })
     })
-    .and(z.record(z.any())) // Allow additional properties from the original feature
+    .and(z.record(z.string(), z.any())) // Allow additional properties from the original feature
 });
 
 // Rasterarray Tileset Feature Schema
diff --git a/src/tools/update-style-tool/UpdateStyleTool.input.schema.ts b/src/tools/update-style-tool/UpdateStyleTool.input.schema.ts
index ef1dcbf..b75dc8e 100644
--- a/src/tools/update-style-tool/UpdateStyleTool.input.schema.ts
+++ b/src/tools/update-style-tool/UpdateStyleTool.input.schema.ts
@@ -9,7 +9,7 @@ export const UpdateStyleInputSchema = z.object({
   styleId: z.string().describe('Style ID to update'),
   name: z.string().optional().describe('New name for the style'),
   style: z
-    .record(z.any())
+    .record(z.string(), z.any())
     .optional()
     .describe(
       'Complete Mapbox Style Specification object to update. Must include: version (8), sources, layers. Optional: sprite, glyphs, center, zoom, bearing, pitch, metadata, etc. See https://docs.mapbox.com/mapbox-gl-js/style-spec/'
diff --git a/src/tools/validate-geojson-tool/ValidateGeojsonTool.input.schema.ts b/src/tools/validate-geojson-tool/ValidateGeojsonTool.input.schema.ts
index cb635ad..84fb26b 100644
--- a/src/tools/validate-geojson-tool/ValidateGeojsonTool.input.schema.ts
+++ b/src/tools/validate-geojson-tool/ValidateGeojsonTool.input.schema.ts
@@ -5,7 +5,7 @@ import { z } from 'zod';
 
 export const ValidateGeojsonInputSchema = z.object({
   geojson: z
-    .union([z.string(), z.record(z.unknown())])
+    .union([z.string(), z.record(z.string(), z.unknown())])
     .describe('GeoJSON object or JSON string to validate')
 });
 
diff --git a/src/tools/validate-style-tool/ValidateStyleTool.input.schema.ts b/src/tools/validate-style-tool/ValidateStyleTool.input.schema.ts
index 21522f0..341542c 100644
--- a/src/tools/validate-style-tool/ValidateStyleTool.input.schema.ts
+++ b/src/tools/validate-style-tool/ValidateStyleTool.input.schema.ts
@@ -9,7 +9,7 @@ import { z } from 'zod';
  */
 export const ValidateStyleInputSchema = z.object({
   style: z
-    .union([z.string(), z.record(z.unknown())])
+    .union([z.string(), z.record(z.string(), z.unknown())])
     .describe(
       'Mapbox style JSON object or JSON string to validate against the Mapbox Style Specification'
     )
diff --git a/test/tools/create-token-tool/CreateTokenTool.test.ts b/test/tools/create-token-tool/CreateTokenTool.test.ts
index 5e336dd..1542202 100644
--- a/test/tools/create-token-tool/CreateTokenTool.test.ts
+++ b/test/tools/create-token-tool/CreateTokenTool.test.ts
@@ -60,7 +60,7 @@ describe('CreateTokenTool', () => {
       expect(result.isError).toBe(true);
       expect(result.content[0]).toHaveProperty('type', 'text');
       const errorText = (result.content[0] as TextContent).text;
-      expect(errorText).toContain('Required');
+      expect(errorText).toContain('invalid_type');
     });
 
     it('validates allowedUrls array length', async () => {
@@ -93,7 +93,7 @@ describe('CreateTokenTool', () => {
       expect(result.isError).toBe(true);
       expect(result.content[0]).toHaveProperty('type', 'text');
       const errorText = (result.content[0] as TextContent).text;
-      expect(errorText).toContain('Invalid enum value');
+      expect(errorText).toContain('invalid_value');
     });
 
     it('throws error when unable to extract username from token', async () => {
diff --git a/test/tools/get-feedback-tool/GetFeedbackTool.test.ts b/test/tools/get-feedback-tool/GetFeedbackTool.test.ts
index ea4d12b..00ef244 100644
--- a/test/tools/get-feedback-tool/GetFeedbackTool.test.ts
+++ b/test/tools/get-feedback-tool/GetFeedbackTool.test.ts
@@ -256,7 +256,7 @@ describe('GetFeedbackTool', () => {
 
     // Should fail validation
     expect(result.isError).toBe(true);
-    expect(result.content[0].text).toContain('Required');
+    expect(result.content[0].text).toContain('invalid_type');
     expect(result.content[0].text).toContain('feedback_id');
   });
 });
diff --git a/test/tools/list-tokens-tool/ListTokensTool.test.ts b/test/tools/list-tokens-tool/ListTokensTool.test.ts
index cfd5aad..1af785c 100644
--- a/test/tools/list-tokens-tool/ListTokensTool.test.ts
+++ b/test/tools/list-tokens-tool/ListTokensTool.test.ts
@@ -59,7 +59,7 @@ describe('ListTokensTool', () => {
       expect(result.isError).toBe(true);
       expect(result.content[0]).toHaveProperty('type', 'text');
       const errorText = (result.content[0] as TextContent).text;
-      expect(errorText).toContain('Number must be less than or equal to 100');
+      expect(errorText).toContain('<=100');
     });
 
     it('validates sortby enum values', async () => {
diff --git a/test/tools/style-comparison-tool/StyleComparisonTool.test.ts b/test/tools/style-comparison-tool/StyleComparisonTool.test.ts
index 78f238f..e715011 100644
--- a/test/tools/style-comparison-tool/StyleComparisonTool.test.ts
+++ b/test/tools/style-comparison-tool/StyleComparisonTool.test.ts
@@ -62,7 +62,7 @@ describe('StyleComparisonTool', () => {
       expect(result.isError).toBe(true);
       expect(
         (result.content[0] as { type: 'text'; text: string }).text
-      ).toContain('Required');
+      ).toContain('invalid_type');
     });
 
     it('should handle full style URLs', async () => {