diff --git a/src/compression.ts b/src/compression.ts
index 4373003..91ebd11 100644
--- a/src/compression.ts
+++ b/src/compression.ts
@@ -1,4 +1,5 @@
 import type { RequestInterceptor, ResponseInterceptor } from "./interceptors.js";
+import { SdkError, SdkErrorCode } from "./errors.js";
 
 export type CompressionAlgorithm = "gzip" | "deflate";
 export type CompressionPayload = string | Uint8Array;
@@ -141,3 +142,77 @@ export function createCompressionResponseInterceptor(_config: CompressionConfig)
     };
   };
 }
+
+// ---------------------------------------------------------------------------
+// #619 — compressMetadata / decompressMetadata
+//
+// JSON + base64url round-trip helpers for storing invoice metadata compactly
+// (e.g. in a Stellar transaction memo or an IPFS payload).
+// ---------------------------------------------------------------------------
+
+/** Default maximum byte size of the encoded base64url string. */
+const DEFAULT_MAX_METADATA_BYTES = 512;
+
+/**
+ * Serializes a metadata object to JSON and encodes it as base64url (no padding).
+ *
+ * @throws {SdkError} with code `CONTRACT_REJECTED` if the resulting base64url
+ *   string exceeds `maxBytes` (default 512).
+ */
+export function compressMetadata(
+  obj: Record<string, unknown>,
+  maxBytes: number = DEFAULT_MAX_METADATA_BYTES,
+): string {
+  const json = JSON.stringify(obj);
+  const encoded = Buffer.from(json, "utf8").toString("base64url");
+
+  if (Buffer.byteLength(encoded, "utf8") > maxBytes) {
+    throw new SdkError(
+      `Compressed metadata exceeds maxBytes (${maxBytes}): got ${Buffer.byteLength(encoded, "utf8")} bytes`,
+      SdkErrorCode.CONTRACT_REJECTED,
+      { actualBytes: Buffer.byteLength(encoded, "utf8"), maxBytes },
+    );
+  }
+
+  return encoded;
+}
+
+/**
+ * Decodes a base64url string and parses the JSON inside it.
+ *
+ * @throws {SdkError} with code `CONTRACT_REJECTED` on invalid base64 input
+ *   or invalid JSON.
+ */
+export function decompressMetadata(encoded: string): Record<string, unknown> {
+  let json: string;
+  try {
+    json = Buffer.from(encoded, "base64url").toString("utf8");
+  } catch {
+    throw new SdkError(
+      "Failed to decode base64url metadata",
+      SdkErrorCode.CONTRACT_REJECTED,
+      { encoded },
+    );
+  }
+
+  let parsed: unknown;
+  try {
+    parsed = JSON.parse(json);
+  } catch {
+    throw new SdkError(
+      "Decompressed metadata is not valid JSON",
+      SdkErrorCode.CONTRACT_REJECTED,
+      { decoded: json.slice(0, 100) },
+    );
+  }
+
+  if (typeof parsed !== "object" || parsed === null || Array.isArray(parsed)) {
+    throw new SdkError(
+      "Decompressed metadata is not a JSON object",
+      SdkErrorCode.CONTRACT_REJECTED,
+      { parsedType: Array.isArray(parsed) ? "array" : typeof parsed },
+    );
+  }
+
+  return parsed as Record<string, unknown>;
+}
diff --git a/src/index.ts b/src/index.ts
index ebf7e30..3cc9c6f 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -1380,3 +1380,10 @@ export type {
   SubmitTransactionOptions,
   SubmitServer,
 } from "./transaction/submit.js";
+
+// ---------------------------------------------------------------------------
+// #619 — compressMetadata / decompressMetadata
+// JSON + base64url round-trip helpers for compact invoice metadata storage
+// ---------------------------------------------------------------------------
+
+export { compressMetadata, decompressMetadata } from "./compression.js";
diff --git a/test/metadataCompression.test.ts b/test/metadataCompression.test.ts
new file mode 100644
index 0000000..8f1394f
--- /dev/null
+++ b/test/metadataCompression.test.ts
@@ -0,0 +1,106 @@
+import { describe, it, expect } from "vitest";
+import {
+  compressMetadata,
+  decompressMetadata,
+} from "../src/compression.js";
+import { SdkError, SdkErrorCode } from "../src/errors.js";
+
+describe("compressMetadata", () => {
+  it("serializes an object to base64url (no padding)", () => {
+    const obj = { amount: "100", asset: "USDC" };
+    const encoded = compressMetadata(obj);
+    // base64url should never contain padding '='
+    expect(encoded).not.toContain("=");
+    expect(encoded).not.toContain("+");
+    expect(encoded).not.toContain("/");
+  });
+
+  it("round-trips a simple object", () => {
+    const obj = { amount: "100", asset: "USDC", memo: "test payment" };
+    const encoded = compressMetadata(obj);
+    const decoded = decompressMetadata(encoded);
+    expect(decoded).toEqual(obj);
+  });
+
+  it("round-trips an empty object", () => {
+    const obj: Record<string, unknown> = {};
+    const encoded = compressMetadata(obj);
+    const decoded = decompressMetadata(encoded);
+    expect(decoded).toEqual({});
+  });
+
+  it("round-trips nested objects and arrays", () => {
+    const obj = {
+      level1: { level2: { level3: "deep" } },
+      items: [1, 2, 3],
+      flag: true,
+      nil: null,
+    };
+    const encoded = compressMetadata(obj);
+    const decoded = decompressMetadata(encoded);
+    expect(decoded).toEqual(obj);
+  });
+
+  it("throws SdkError CONTRACT_REJECTED when exceeding maxBytes", () => {
+    const obj = { data: "x".repeat(1000) };
+    expect(() => compressMetadata(obj, 100)).toThrow(SdkError);
+    try {
+      compressMetadata(obj, 100);
+    } catch (e) {
+      expect(e).toBeInstanceOf(SdkError);
+      expect((e as SdkError).code).toBe(SdkErrorCode.CONTRACT_REJECTED);
+    }
+  });
+
+  it("respects custom maxBytes argument", () => {
+    const obj = { short: "ok" };
+    // Should fit within a generous limit
+    expect(() => compressMetadata(obj, 512)).not.toThrow();
+    // Should fail with a tiny limit
+    expect(() => compressMetadata(obj, 1)).toThrow(SdkError);
+  });
+});
+
+describe("decompressMetadata", () => {
+  it("throws SdkError CONTRACT_REJECTED on invalid base64 input", () => {
+    // Not valid base64url — contains characters outside the alphabet
+    expect(() => decompressMetadata("!!!notbase64!!!")).toThrow(SdkError);
+    try {
+      decompressMetadata("!!!notbase64!!!");
+    } catch (e) {
+      expect(e).toBeInstanceOf(SdkError);
+      expect((e as SdkError).code).toBe(SdkErrorCode.CONTRACT_REJECTED);
+    }
+  });
+
+  it("throws SdkError CONTRACT_REJECTED on valid base64 but invalid JSON", () => {
+    // "not json" encoded as base64url
+    const encoded = Buffer.from("not json").toString("base64url");
+    expect(() => decompressMetadata(encoded)).toThrow(SdkError);
+    try {
+      decompressMetadata(encoded);
+    } catch (e) {
+      expect(e).toBeInstanceOf(SdkError);
+      expect((e as SdkError).code).toBe(SdkErrorCode.CONTRACT_REJECTED);
+    }
+  });
+
+  it("throws SdkError CONTRACT_REJECTED when decoded JSON is not an object", () => {
+    // JSON array
+    const encoded = Buffer.from("[1, 2, 3]").toString("base64url");
+    expect(() => decompressMetadata(encoded)).toThrow(SdkError);
+    // JSON string
+    const strEncoded = Buffer.from('"hello"').toString("base64url");
+    expect(() => decompressMetadata(strEncoded)).toThrow(SdkError);
+    // JSON number
+    const numEncoded = Buffer.from("42").toString("base64url");
+    expect(() => decompressMetadata(numEncoded)).toThrow(SdkError);
+  });
+
+  it("decodes a previously compressed object correctly", () => {
+    const original = { invoiceId: "inv_123", total: "500.00", currency: "USDC" };
+    const encoded = compressMetadata(original);
+    const decoded = decompressMetadata(encoded);
+    expect(decoded).toEqual(original);
+  });
+});