diff --git a/common/changes/@rushstack/node-core-library/rf-jsonschema-add-custom-formats_2024-09-10-03-15.json b/common/changes/@rushstack/node-core-library/rf-jsonschema-add-custom-formats_2024-09-10-03-15.json
new file mode 100644
index 00000000000..339b3b8649d
--- /dev/null
+++ b/common/changes/@rushstack/node-core-library/rf-jsonschema-add-custom-formats_2024-09-10-03-15.json
@@ -0,0 +1,10 @@
+{
+  "changes": [
+    {
+      "packageName": "@rushstack/node-core-library",
+      "comment": "Add a `customFormats` option to `JsonSchema`.",
+      "type": "minor"
+    }
+  ],
+  "packageName": "@rushstack/node-core-library"
+}
\ No newline at end of file
diff --git a/common/reviews/api/node-core-library.api.md b/common/reviews/api/node-core-library.api.md
index 4c7786d3668..842a74830bb 100644
--- a/common/reviews/api/node-core-library.api.md
+++ b/common/reviews/api/node-core-library.api.md
@@ -423,6 +423,12 @@ export interface IJsonFileStringifyOptions extends IJsonFileParseOptions {
     prettyFormatting?: boolean;
 }
 
+// @public
+export interface IJsonSchemaCustomFormat<T extends string | number> {
+    type: T extends string ? 'string' : T extends number ? 'number' : never;
+    validate: (data: T) => boolean;
+}
+
 // @public
 export interface IJsonSchemaErrorInfo {
     details: string;
@@ -436,6 +442,7 @@ export type IJsonSchemaFromObjectOptions = IJsonSchemaLoadOptions;
 
 // @public
 export interface IJsonSchemaLoadOptions {
+    customFormats?: Record<string, IJsonSchemaCustomFormat<string> | IJsonSchemaCustomFormat<number>>;
     dependentSchemas?: JsonSchema[];
     schemaVersion?: JsonSchemaVersion;
 }
diff --git a/libraries/node-core-library/src/JsonSchema.ts b/libraries/node-core-library/src/JsonSchema.ts
index fd68ad65302..dcbe8e81052 100644
--- a/libraries/node-core-library/src/JsonSchema.ts
+++ b/libraries/node-core-library/src/JsonSchema.ts
@@ -25,6 +25,24 @@ interface ISchemaWithId {
  */
 export type JsonSchemaVersion = 'draft-04' | 'draft-07';
 
+/**
+ * A definition for a custom format to consider during validation.
+ * @public
+ */
+export interface IJsonSchemaCustomFormat<T extends string | number> {
+  /**
+   * The base JSON type.
+   */
+  type: T extends string ? 'string' : T extends number ? 'number' : never;
+
+  /**
+   * A validation function for the format.
+   * @param data - The raw field data to validate.
+   * @returns whether the data is valid according to the format.
+   */
+  validate: (data: T) => boolean;
+}
+
 /**
  * Callback function arguments for {@link JsonSchema.validateObjectWithCallback}
  * @public
@@ -94,6 +112,13 @@ export interface IJsonSchemaLoadOptions {
    * or does not match an expected URL, the default version will be used.
    */
   schemaVersion?: JsonSchemaVersion;
+
+  /**
+   * Any custom formats to consider during validation. Some standard formats are supported
+   * out-of-the-box (e.g. emails, uris), but additional formats can be defined here. You could
+   * for example define generic numeric formats (e.g. uint8) or domain-specific formats.
+   */
+  customFormats?: Record<string, IJsonSchemaCustomFormat<string> | IJsonSchemaCustomFormat<number>>;
 }
 
 /**
@@ -141,6 +166,9 @@ export class JsonSchema {
   private _validator: ValidateFunction | undefined = undefined;
   private _schemaObject: JsonObject | undefined = undefined;
   private _schemaVersion: JsonSchemaVersion | undefined = undefined;
+  private _customFormats:
+    | Record<string, IJsonSchemaCustomFormat<string> | IJsonSchemaCustomFormat<number>>
+    | undefined = undefined;
 
   private constructor() {}
 
@@ -163,6 +191,7 @@ export class JsonSchema {
     if (options) {
       schema._dependentSchemas = options.dependentSchemas || [];
       schema._schemaVersion = options.schemaVersion;
+      schema._customFormats = options.customFormats;
     }
 
     return schema;
@@ -181,6 +210,7 @@ export class JsonSchema {
     if (options) {
       schema._dependentSchemas = options.dependentSchemas || [];
       schema._schemaVersion = options.schemaVersion;
+      schema._customFormats = options.customFormats;
     }
 
     return schema;
@@ -308,6 +338,11 @@ export class JsonSchema {
       // Enable json-schema format validation
       // https://ajv.js.org/packages/ajv-formats.html
       addFormats(validator);
+      if (this._customFormats) {
+        for (const [name, format] of Object.entries(this._customFormats)) {
+          validator.addFormat(name, { ...format, async: false });
+        }
+      }
 
       const collectedSchemas: JsonSchema[] = [];
       const seenObjects: Set<JsonSchema> = new Set<JsonSchema>();
diff --git a/libraries/node-core-library/src/index.ts b/libraries/node-core-library/src/index.ts
index 70396912fbc..54fb6509b7a 100644
--- a/libraries/node-core-library/src/index.ts
+++ b/libraries/node-core-library/src/index.ts
@@ -65,6 +65,7 @@ export {
 } from './JsonFile';
 export {
   type IJsonSchemaErrorInfo,
+  type IJsonSchemaCustomFormat,
   type IJsonSchemaFromFileOptions,
   type IJsonSchemaFromObjectOptions,
   type IJsonSchemaLoadOptions,
diff --git a/libraries/node-core-library/src/test/JsonSchema.test.ts b/libraries/node-core-library/src/test/JsonSchema.test.ts
index b4a82de4576..e2d537056ae 100644
--- a/libraries/node-core-library/src/test/JsonSchema.test.ts
+++ b/libraries/node-core-library/src/test/JsonSchema.test.ts
@@ -119,4 +119,32 @@ describe(JsonSchema.name, () => {
       expect(errorDetails).toMatchSnapshot();
     });
   });
+
+  test('successfully applies custom formats', () => {
+    const schemaWithCustomFormat = JsonSchema.fromLoadedObject(
+      {
+        title: 'Test Custom Format',
+        type: 'object',
+        properties: {
+          exampleNumber: {
+            type: 'number',
+            format: 'uint8'
+          }
+        },
+        additionalProperties: false,
+        required: ['exampleNumber']
+      },
+      {
+        schemaVersion: 'draft-07',
+        customFormats: {
+          uint8: {
+            type: 'number',
+            validate: (data) => data >= 0 && data <= 255
+          }
+        }
+      }
+    );
+    expect(() => schemaWithCustomFormat.validateObject({ exampleNumber: 10 }, '')).not.toThrow();
+    expect(() => schemaWithCustomFormat.validateObject({ exampleNumber: 1000 }, '')).toThrow();
+  });
 });