diff --git a/Backend/package.json b/Backend/package.json
index f5c30d53..143af2d4 100644
--- a/Backend/package.json
+++ b/Backend/package.json
@@ -87,6 +87,12 @@
     "transform": {
       "^.+\\.(t|j)s$": "ts-jest"
     },
+    "transformIgnorePatterns": [
+      "node_modules/(?!(@stellar/stellar-sdk|@noble)/)"
+    ],
+    "moduleNameMapper": {
+      "^src/(.*)$": "<rootDir>/$1"
+    },
     "collectCoverageFrom": [
       "**/*.(t|j)s"
     ],
diff --git a/Backend/src/common/validators/index.ts b/Backend/src/common/validators/index.ts
new file mode 100644
index 00000000..35e4316d
--- /dev/null
+++ b/Backend/src/common/validators/index.ts
@@ -0,0 +1 @@
+export { IsStellarAddress } from './stellar-address.validator';
diff --git a/Backend/src/common/validators/stellar-address.validator.spec.ts b/Backend/src/common/validators/stellar-address.validator.spec.ts
new file mode 100644
index 00000000..79e01a58
--- /dev/null
+++ b/Backend/src/common/validators/stellar-address.validator.spec.ts
@@ -0,0 +1,54 @@
+import { validate } from 'class-validator';
+import { IsOptional } from 'class-validator';
+
+// Mock @stellar/stellar-sdk before importing the validator
+jest.mock('@stellar/stellar-sdk', () => ({
+  StrKey: {
+    isValidEd25519PublicKey: (value: string) =>
+      typeof value === 'string' && value.length === 55 && /^G[A-Z2-7]{54}$/.test(value),
+  },
+}));
+
+import { IsStellarAddress } from './stellar-address.validator';
+
+class TestDto {
+  @IsOptional()
+  @IsStellarAddress()
+  authorAddress?: string;
+}
+
+const VALID_ADDRESS = 'GAAZI4TCR3TY5OJHCTJC2A4QSY6CJWJH5IAJTGKIN2ER7LBNVKOCCWN';
+
+describe('IsStellarAddress', () => {
+  it('passes with a valid Stellar public key', async () => {
+    const dto = Object.assign(new TestDto(), { authorAddress: VALID_ADDRESS });
+    const errors = await validate(dto);
+    expect(errors).toHaveLength(0);
+  });
+
+  it('passes when authorAddress is absent (anonymous post)', async () => {
+    const errors = await validate(new TestDto());
+    expect(errors).toHaveLength(0);
+  });
+
+  it('fails with an invalid string', async () => {
+    const dto = Object.assign(new TestDto(), { authorAddress: 'not-a-stellar-key' });
+    const errors = await validate(dto);
+    expect(errors).toHaveLength(1);
+    expect(errors[0].constraints?.isStellarAddress).toBe(
+      'authorAddress must be a valid Stellar public key',
+    );
+  });
+
+  it('fails with an address that does not start with G', async () => {
+    const dto = Object.assign(new TestDto(), { authorAddress: 'XAAZI4TCR3TY5OJHCTJC2A4QSY6CJWJH5IAJTGKIN2ER7LBNVKOCCWN' });
+    const errors = await validate(dto);
+    expect(errors).toHaveLength(1);
+  });
+
+  it('fails with an empty string', async () => {
+    const dto = Object.assign(new TestDto(), { authorAddress: '' });
+    const errors = await validate(dto);
+    expect(errors).toHaveLength(1);
+  });
+});
diff --git a/Backend/src/common/validators/stellar-address.validator.ts b/Backend/src/common/validators/stellar-address.validator.ts
new file mode 100644
index 00000000..fedd47b2
--- /dev/null
+++ b/Backend/src/common/validators/stellar-address.validator.ts
@@ -0,0 +1,21 @@
+import { registerDecorator, ValidationOptions } from 'class-validator';
+import { StrKey } from '@stellar/stellar-sdk';
+
+export function IsStellarAddress(validationOptions?: ValidationOptions) {
+  return function (object: object, propertyName: string) {
+    registerDecorator({
+      name: 'isStellarAddress',
+      target: object.constructor,
+      propertyName,
+      options: validationOptions,
+      validator: {
+        validate(value: unknown) {
+          return typeof value === 'string' && StrKey.isValidEd25519PublicKey(value);
+        },
+        defaultMessage() {
+          return 'authorAddress must be a valid Stellar public key';
+        },
+      },
+    });
+  };
+}
diff --git a/Backend/src/gists/dto/create-gist.dto.ts b/Backend/src/gists/dto/create-gist.dto.ts
index be2dc003..2bbc261b 100644
--- a/Backend/src/gists/dto/create-gist.dto.ts
+++ b/Backend/src/gists/dto/create-gist.dto.ts
@@ -20,10 +20,12 @@ export class CreateGistDto {
   lon: number;
 
   @ApiPropertyOptional({
-    description: 'Optional Stellar address of the author',
-    example: 'GABC...XYZ',
+    description: 'Optional Stellar public key of the author (Ed25519, starts with G, 56 chars)',
+    example: 'GAAZI4TCR3TY5OJHCTJC2A4QSY6CJWJH5IAJTGKIN2ER7LBNVKOCCWN',
   })
   @IsOptional()
+  @IsStellarAddress()
+  authorAddress?: string;
   @IsString()
   @MaxLength(80)
   author?: string;