fix: strip unsupported JSON Schema format values for OpenAI compatibility

src/utils/__tests__/json-schema.spec.ts

@@ -265,4 +265,183 @@ describe("normalizeToolSchema", () => {
 		expect(props.line_ranges.items).toBeDefined()
 		expect(props.line_ranges.description).toBe("Optional line ranges")
 	})
+
+	describe("format field handling", () => {
+		it("should preserve supported format values (date-time)", () => {
+			const input = {
+				type: "string",
+				format: "date-time",
+				description: "Timestamp",
+			}
+
+			const result = normalizeToolSchema(input)
+
+			expect(result).toEqual({
+				type: "string",
+				format: "date-time",
+				description: "Timestamp",
+				additionalProperties: false,
+			})
+		})
+
+		it("should preserve supported format values (email)", () => {
+			const input = {
+				type: "string",
+				format: "email",
+			}
+
+			const result = normalizeToolSchema(input)
+
+			expect(result.format).toBe("email")
+		})
+
+		it("should preserve supported format values (uuid)", () => {
+			const input = {
+				type: "string",
+				format: "uuid",
+			}
+
+			const result = normalizeToolSchema(input)
+
+			expect(result.format).toBe("uuid")
+		})
+
+		it("should preserve all supported format values", () => {
+			const supportedFormats = [
+				"date-time",
+				"time",
+				"date",
+				"duration",
+				"email",
+				"hostname",
+				"ipv4",
+				"ipv6",
+				"uuid",
+			]
+
+			for (const format of supportedFormats) {
+				const input = { type: "string", format }
+				const result = normalizeToolSchema(input)
+				expect(result.format).toBe(format)
+			}
+		})
+
+		it("should strip unsupported format value (uri)", () => {
+			const input = {
+				type: "string",
+				format: "uri",
+				description: "URL field",
+			}
+
+			const result = normalizeToolSchema(input)
+
+			expect(result).toEqual({
+				type: "string",
+				description: "URL field",
+				additionalProperties: false,
+			})
+			expect(result.format).toBeUndefined()
+		})
+
+		it("should strip unsupported format value (uri-reference)", () => {
+			const input = {
+				type: "string",
+				format: "uri-reference",
+			}
+
+			const result = normalizeToolSchema(input)
+
+			expect(result.format).toBeUndefined()
+		})
+
+		it("should strip unsupported format values (various)", () => {
+			const unsupportedFormats = ["uri", "uri-reference", "iri", "iri-reference", "regex", "json-pointer"]
+
+			for (const format of unsupportedFormats) {
+				const input = { type: "string", format }
+				const result = normalizeToolSchema(input)
+				expect(result.format).toBeUndefined()
+			}
+		})
+
+		it("should strip unsupported format in nested properties", () => {
+			const input = {
+				type: "object",
+				properties: {
+					url: {
+						type: "string",
+						format: "uri",
+						description: "A URL",
+					},
+					email: {
+						type: "string",
+						format: "email",
+						description: "An email",
+					},
+				},
+			}
+
+			const result = normalizeToolSchema(input)
+
+			const props = result.properties as Record<string, Record<string, unknown>>
+			expect(props.url.format).toBeUndefined()
+			expect(props.url.description).toBe("A URL")
+			expect(props.email.format).toBe("email")
+			expect(props.email.description).toBe("An email")
+		})
+
+		it("should strip unsupported format in deeply nested structures", () => {
+			const input = {
+				type: "object",
+				properties: {
+					items: {
+						type: "array",
+						items: {
+							type: "object",
+							properties: {
+								link: {
+									type: "string",
+									format: "uri",
+								},
+								timestamp: {
+									type: "string",
+									format: "date-time",
+								},
+							},
+						},
+					},
+				},
+			}
+
+			const result = normalizeToolSchema(input)
+
+			const props = result.properties as Record<string, Record<string, unknown>>
+			const itemsItems = props.items.items as Record<string, unknown>
+			const nestedProps = itemsItems.properties as Record<string, Record<string, unknown>>
+			expect(nestedProps.link.format).toBeUndefined()
+			expect(nestedProps.timestamp.format).toBe("date-time")
+		})
+
+		it("should handle MCP fetch server schema with uri format", () => {
+			// This is similar to the actual fetch MCP server schema that caused the error
+			const input = {
+				type: "object",
+				properties: {
+					url: {
+						type: "string",
+						format: "uri",
+						description: "URL to fetch",
+					},
+				},
+				required: ["url"],
+			}
+
+			const result = normalizeToolSchema(input)
+
+			const props = result.properties as Record<string, Record<string, unknown>>
+			expect(props.url.format).toBeUndefined()
+			expect(props.url.type).toBe("string")
+			expect(props.url.description).toBe("URL to fetch")
+		})
+	})
 })

src/utils/json-schema.ts

@@ -6,6 +6,23 @@ import { z } from "zod"
  */
 export type JsonSchema = z4.core.JSONSchema.JSONSchema
 
+/**
+ * Set of format values supported by OpenAI's Structured Outputs (strict mode).
+ * Unsupported format values will be stripped during schema normalization.
+ * @see https://platform.openai.com/docs/guides/structured-outputs#supported-schemas
+ */
+const OPENAI_SUPPORTED_FORMATS = new Set([
+	"date-time",
+	"time",
+	"date",
+	"duration",
+	"email",
+	"hostname",
+	"ipv4",
+	"ipv6",
+	"uuid",
+])
+
 /**
  * Zod schema for JSON Schema primitive types
  */
@@ -76,10 +93,11 @@ const TypeFieldSchema = z.union([JsonSchemaTypeSchema, z.array(JsonSchemaTypeSch
 /**
  * Internal Zod schema that normalizes tool input JSON Schema to be compliant with JSON Schema draft 2020-12.
  *
- * This schema performs two key transformations:
+ * This schema performs three key transformations:
  * 1. Sets `additionalProperties: false` by default (required by OpenAI strict mode)
  * 2. Converts deprecated `type: ["T", "null"]` array syntax to `anyOf` format
  *    (required by Claude on Bedrock which enforces JSON Schema draft 2020-12)
+ * 3. Strips unsupported `format` values (e.g., "uri") for OpenAI Structured Outputs compatibility
  *
  * Uses recursive parsing so transformations apply to all nested schemas automatically.
  */
@@ -109,10 +127,12 @@ const NormalizedToolSchemaInternal: z.ZodType<Record<string, unknown>, z.ZodType
 				minItems: z.number().optional(),
 				maxItems: z.number().optional(),
 				uniqueItems: z.boolean().optional(),
+				// Format field - unsupported values will be stripped in transform
+				format: z.string().optional(),
 			})
 			.passthrough()
 			.transform((schema) => {
-				const { type, required, properties, ...rest } = schema
+				const { type, required, properties, format, ...rest } = schema
 				const result: Record<string, unknown> = { ...rest }
 
 				// If type is an array, convert to anyOf format (JSON Schema 2020-12)
@@ -122,6 +142,12 @@ const NormalizedToolSchemaInternal: z.ZodType<Record<string, unknown>, z.ZodType
 					result.type = type
 				}
 
+				// Strip unsupported format values for OpenAI compatibility
+				// Only include format if it's a supported value
+				if (format && OPENAI_SUPPORTED_FORMATS.has(format)) {
+					result.format = format
+				}
+
 				// Handle properties and required for strict mode
 				if (properties) {
 					result.properties = properties
@@ -145,10 +171,11 @@ const NormalizedToolSchemaInternal: z.ZodType<Record<string, unknown>, z.ZodType
 /**
  * Normalizes a tool input JSON Schema to be compliant with JSON Schema draft 2020-12.
  *
- * This function performs two key transformations:
+ * This function performs three key transformations:
  * 1. Sets `additionalProperties: false` by default (required by OpenAI strict mode)
  * 2. Converts deprecated `type: ["T", "null"]` array syntax to `anyOf` format
  *    (required by Claude on Bedrock which enforces JSON Schema draft 2020-12)
+ * 3. Strips unsupported `format` values (e.g., "uri") for OpenAI Structured Outputs compatibility
  *
  * Uses recursive parsing so transformations apply to all nested schemas automatically.
  *