From 2f5993b412032b043dacc3dcf3a3badd055c302c Mon Sep 17 00:00:00 2001
From: saripovdenis <iam.saripov.denis@gmail.com>
Date: Tue, 28 Apr 2026 17:19:58 +0800
Subject: [PATCH 01/12] perf: skip encoding safe cookie values

---
 src/index.ts | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/src/index.ts b/src/index.ts
index a95a2e9..33753c9 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -68,6 +68,8 @@ const pathValueRegExp = /^[\u0020-\u003A\u003D-\u007E]*$/;
  */
 const maxAgeRegExp = /^-?\d+$/;
 
+const noEncodeRegExp = /^[\w.!~*'()-]*$/;
+
 const __toString = Object.prototype.toString;
 
 const NullObject = /* @__PURE__ */ (() => {
@@ -157,7 +159,7 @@ export function stringifyCookie(
   cookie: Cookies,
   options?: StringifyOptions,
 ): string {
-  const enc = options?.encode || encodeURIComponent;
+  const enc = options?.encode || encode;
   const keys = Object.keys(cookie);
   let str = "";
 
@@ -534,6 +536,13 @@ function decode(str: string): string {
   }
 }
 
+/**
+ * URL-encode string value. Optimized to skip native call when no escaping is needed.
+ */
+function encode(str: string): string {
+  return noEncodeRegExp.test(str) ? str : encodeURIComponent(str);
+}
+
 /**
  * Determine if value is a Date.
  */

From 72ffbeb778f2dbaaac509fb520a49ff1454ed712 Mon Sep 17 00:00:00 2001
From: saripovdenis <iam.saripov.denis@gmail.com>
Date: Tue, 28 Apr 2026 22:35:15 +0800
Subject: [PATCH 02/12] test: verify default cookie encoding

---
 src/stringify-cookie.spec.ts | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/src/stringify-cookie.spec.ts b/src/stringify-cookie.spec.ts
index 9edcfde..c0206d5 100644
--- a/src/stringify-cookie.spec.ts
+++ b/src/stringify-cookie.spec.ts
@@ -36,6 +36,33 @@ describe("cookie.stringifyCookie", () => {
     );
   });
 
+  it("should match encodeURIComponent for default encoding", () => {
+    const mismatches: string[] = [];
+
+    for (let code = 0; code <= 0xffff; code++) {
+      if (code >= 0xd800 && code <= 0xdfff) continue;
+
+      const value = String.fromCharCode(code);
+      const actual = stringifyCookie({ key: value });
+      const expected = `key=${encodeURIComponent(value)}`;
+
+      if (actual !== expected) {
+        mismatches.push(`${code}: ${actual} !== ${expected}`);
+      }
+    }
+
+    for (const value of ["😄", "𝌆", "𠜎"]) {
+      const actual = stringifyCookie({ key: value });
+      const expected = `key=${encodeURIComponent(value)}`;
+
+      if (actual !== expected) {
+        mismatches.push(`${value}: ${actual} !== ${expected}`);
+      }
+    }
+
+    expect(mismatches).toEqual([]);
+  });
+
   it("should error on invalid keys", () => {
     expect(() => stringifyCookie({ "test=": "" })).toThrow(
       /cookie name is invalid/,

From b3cb3eff0362cf48c0531d8cd49e79d3d22aeed8 Mon Sep 17 00:00:00 2001
From: saripovdenis <iam.saripov.denis@gmail.com>
Date: Tue, 28 Apr 2026 23:05:10 +0800
Subject: [PATCH 03/12] bench: add encoded stringify cookie cases

---
 src/stringify-cookie.bench.ts | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/src/stringify-cookie.bench.ts b/src/stringify-cookie.bench.ts
index 9da3464..67d96a6 100644
--- a/src/stringify-cookie.bench.ts
+++ b/src/stringify-cookie.bench.ts
@@ -10,6 +10,10 @@ describe("cookie.stringifyCookie", () => {
     cookie.stringifyCookie({ foo: "bar" });
   });
 
+  bench("encode", () => {
+    cookie.stringifyCookie({ foo: "bar baz;%" });
+  });
+
   bench("undefined values", () => {
     cookie.stringifyCookie({
       foo: "bar",
@@ -19,6 +23,14 @@ describe("cookie.stringifyCookie", () => {
     });
   });
 
+  bench("mixed encode", () => {
+    cookie.stringifyCookie({
+      foo: "bar",
+      baz: "quux zap",
+      qux: "quux",
+    });
+  });
+
   const cookies10 = genCookies(10);
   bench("10 cookies", () => {
     cookie.stringifyCookie(cookies10);

From e113fdc988bfb1958fa964c2f0e0bb70c8bc1408 Mon Sep 17 00:00:00 2001
From: saripovdenis <iam.saripov.denis@gmail.com>
Date: Sun, 3 May 2026 00:56:26 +0800
Subject: [PATCH 04/12] perf: skip encoding valid cookie octets

---
 README.md                        |  6 +++---
 src/index.ts                     | 14 +++++++++-----
 src/stringify-cookie.spec.ts     | 26 ++++++++++++++++++++++----
 src/stringify-set-cookie.spec.ts | 10 +++++++++-
 4 files changed, 43 insertions(+), 13 deletions(-)

diff --git a/README.md b/README.md
index 09cb444..2feb3c3 100644
--- a/README.md
+++ b/README.md
@@ -48,7 +48,7 @@ const cookieHeader = cookie.stringifyCookie({ a: "foo", b: "bar" });
 
 #### Options
 
-- `encode` Specifies the function to encode a [cookie-value](https://datatracker.ietf.org/doc/html/rfc6265#section-4.1.1). Defaults to [`encodeURIComponent`](#encode-and-decode).
+- `encode` Specifies the function to encode a [cookie-value](https://datatracker.ietf.org/doc/html/rfc6265#section-4.1.1). Defaults to preserving valid cookie-octet values and using [`encodeURIComponent`](#encode-and-decode) otherwise.
 
 ### cookie.parseSetCookie(str, options)
 
@@ -88,7 +88,7 @@ const setCookieHeader = cookie.stringifySetCookie({
 
 #### Options
 
-- `encode` Specifies the function to encode a [cookie-value](https://datatracker.ietf.org/doc/html/rfc6265#section-4.1.1). Defaults to [`encodeURIComponent`](#encode-and-decode).
+- `encode` Specifies the function to encode a [cookie-value](https://datatracker.ietf.org/doc/html/rfc6265#section-4.1.1). Defaults to preserving valid cookie-octet values and using [`encodeURIComponent`](#encode-and-decode) otherwise.
 
 ## Cookie object
 
@@ -178,7 +178,7 @@ More information about enforcement levels can be found in [the specification](ht
 Cookie accepts `encode` or `decode` options for processing a [cookie-value](https://datatracker.ietf.org/doc/html/rfc6265#section-4.1.1).
 Since the value of a cookie has a limited character set (and must be a simple string), these functions are used to transform values into strings suitable for a cookies value.
 
-The default `encode` function is the global `encodeURIComponent`.
+The default `encode` function preserves valid RFC 6265 cookie-octet values and uses the global `encodeURIComponent` otherwise.
 
 The default `decode` function is the global `decodeURIComponent`, wrapped in a `try..catch`. If an error
 is thrown it will return the cookie's original value. If you provide your own encode/decode
diff --git a/src/index.ts b/src/index.ts
index 33753c9..169953b 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -68,7 +68,10 @@ const pathValueRegExp = /^[\u0020-\u003A\u003D-\u007E]*$/;
  */
 const maxAgeRegExp = /^-?\d+$/;
 
-const noEncodeRegExp = /^[\w.!~*'()-]*$/;
+/**
+ * RegExp to match RFC 6265 cookie-octet values that need no URL encoding.
+ */
+const cookieOctetRegExp = /^[!#$%&'()*+\-.\/0-9:<=>?@A-Z[\]\^_`a-z{|}~]*$/;
 
 const __toString = Object.prototype.toString;
 
@@ -146,8 +149,9 @@ export interface StringifyOptions {
    * Specifies a function that will be used to encode a [cookie-value](https://datatracker.ietf.org/doc/html/rfc6265#section-4.1.1).
    * Since value of a cookie has a limited character set (and must be a simple string), this function can be used to encode
    * a value into a string suited for a cookie's value, and should mirror `decode` when parsing.
+   * The default function preserves valid RFC 6265 cookie-octet values and uses `encodeURIComponent` otherwise.
    *
-   * @default encodeURIComponent
+   * @default encode
    */
   encode?: (str: string) => string;
 }
@@ -300,7 +304,7 @@ export function stringifySetCookie(
       ? _name
       : { ..._opts, name: _name, value: String(_val) };
   const options = typeof _val === "object" ? _val : _opts;
-  const enc = options?.encode || encodeURIComponent;
+  const enc = options?.encode || encode;
 
   if (!cookieNameRegExp.test(cookie.name)) {
     throw new TypeError(`argument name is invalid: ${cookie.name}`);
@@ -537,10 +541,10 @@ function decode(str: string): string {
 }
 
 /**
- * URL-encode string value. Optimized to skip native call when no escaping is needed.
+ * URL-encode string value. Optimized to skip native call for RFC 6265 cookie-octet values.
  */
 function encode(str: string): string {
-  return noEncodeRegExp.test(str) ? str : encodeURIComponent(str);
+  return cookieOctetRegExp.test(str) ? str : encodeURIComponent(str);
 }
 
 /**
diff --git a/src/stringify-cookie.spec.ts b/src/stringify-cookie.spec.ts
index c0206d5..11f89fa 100644
--- a/src/stringify-cookie.spec.ts
+++ b/src/stringify-cookie.spec.ts
@@ -28,15 +28,30 @@ describe("cookie.stringifyCookie", () => {
     expect(stringifyCookie({ a: "", b: "" })).toEqual("a=; b=");
   });
 
-  it("should URL-encode values by default", () => {
+  it("should encode values with non-cookie-octet chars by default", () => {
     expect(stringifyCookie({ foo: "bar baz" })).toEqual("foo=bar%20baz");
-    expect(stringifyCookie({ foo: "a=b" })).toEqual("foo=a%3Db");
     expect(stringifyCookie({ foo: "hello;world" })).toEqual(
       "foo=hello%3Bworld",
     );
+    expect(stringifyCookie({ foo: 'hello"world' })).toEqual(
+      "foo=hello%22world",
+    );
+    expect(stringifyCookie({ foo: "foo,bar" })).toEqual("foo=foo%2Cbar");
+    expect(stringifyCookie({ foo: "foo\\bar" })).toEqual("foo=foo%5Cbar");
   });
 
-  it("should match encodeURIComponent for default encoding", () => {
+  it("should pass through cookie-octet values by default", () => {
+    const value =
+      "!#$%&'()*+-./0123456789:<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[]" +
+      "^_`abcdefghijklmnopqrstuvwxyz{|}~";
+
+    expect(stringifyCookie({ foo: value })).toEqual(`foo=${value}`);
+  });
+
+  it("should match cookie-octet default encoding", () => {
+    const cookieOctets =
+      "!#$%&'()*+-./0123456789:<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[]" +
+      "^_`abcdefghijklmnopqrstuvwxyz{|}~";
     const mismatches: string[] = [];
 
     for (let code = 0; code <= 0xffff; code++) {
@@ -44,7 +59,10 @@ describe("cookie.stringifyCookie", () => {
 
       const value = String.fromCharCode(code);
       const actual = stringifyCookie({ key: value });
-      const expected = `key=${encodeURIComponent(value)}`;
+      const encoded = cookieOctets.includes(value)
+        ? value
+        : encodeURIComponent(value);
+      const expected = `key=${encoded}`;
 
       if (actual !== expected) {
         mismatches.push(`${code}: ${actual} !== ${expected}`);
diff --git a/src/stringify-set-cookie.spec.ts b/src/stringify-set-cookie.spec.ts
index 92a56ea..3b718f2 100644
--- a/src/stringify-set-cookie.spec.ts
+++ b/src/stringify-set-cookie.spec.ts
@@ -10,12 +10,20 @@ describe("cookie.stringifySetCookie", function () {
     expect(cookie.stringifySetCookie("foo", "bar")).toEqual("foo=bar");
   });
 
-  it("should URL-encode value", function () {
+  it("should encode values with non-cookie-octet chars", function () {
     expect(cookie.stringifySetCookie("foo", "bar +baz")).toEqual(
       "foo=bar%20%2Bbaz",
     );
   });
 
+  it("should pass through cookie-octet values", function () {
+    const value =
+      "!#$%&'()*+-./0123456789:<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[]" +
+      "^_`abcdefghijklmnopqrstuvwxyz{|}~";
+
+    expect(cookie.stringifySetCookie("foo", value)).toEqual(`foo=${value}`);
+  });
+
   it("should serialize empty value", function () {
     expect(cookie.stringifySetCookie("foo", "")).toEqual("foo=");
   });

From f7e1bc905e0a89fc6d4036a56de5191c1a0574e0 Mon Sep 17 00:00:00 2001
From: saripovdenis <iam.saripov.denis@gmail.com>
Date: Sun, 3 May 2026 01:06:34 +0800
Subject: [PATCH 05/12] bench: add RFC cookie-octet stringify case

---
 src/stringify-cookie.bench.ts | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/src/stringify-cookie.bench.ts b/src/stringify-cookie.bench.ts
index 67d96a6..a882aaf 100644
--- a/src/stringify-cookie.bench.ts
+++ b/src/stringify-cookie.bench.ts
@@ -10,6 +10,10 @@ describe("cookie.stringifyCookie", () => {
     cookie.stringifyCookie({ foo: "bar" });
   });
 
+  bench("rfc cookie-octets", () => {
+    cookie.stringifyCookie({ foo: "a=b+c/d?x%20" });
+  });
+
   bench("encode", () => {
     cookie.stringifyCookie({ foo: "bar baz;%" });
   });

From 911ec0f1fd9b40cd87a68faca29ef4cf90072c66 Mon Sep 17 00:00:00 2001
From: saripovdenis <iam.saripov.denis@gmail.com>
Date: Tue, 12 May 2026 01:01:52 +0800
Subject: [PATCH 06/12] fix: remove % from cookieOctetRegExp to preserve
 decode(encode(%20)) roundtrip

---
 README.md                        |  6 +++---
 src/index.ts                     |  8 ++++----
 src/stringify-cookie.bench.ts    |  2 +-
 src/stringify-cookie.spec.ts     | 19 +++++++++++++++----
 src/stringify-set-cookie.spec.ts |  4 ++--
 5 files changed, 25 insertions(+), 14 deletions(-)

diff --git a/README.md b/README.md
index 2feb3c3..1182c2a 100644
--- a/README.md
+++ b/README.md
@@ -48,7 +48,7 @@ const cookieHeader = cookie.stringifyCookie({ a: "foo", b: "bar" });
 
 #### Options
 
-- `encode` Specifies the function to encode a [cookie-value](https://datatracker.ietf.org/doc/html/rfc6265#section-4.1.1). Defaults to preserving valid cookie-octet values and using [`encodeURIComponent`](#encode-and-decode) otherwise.
+- `encode` Specifies the function to encode a [cookie-value](https://datatracker.ietf.org/doc/html/rfc6265#section-4.1.1). Defaults to preserving roundtrip-safe cookie-octet values and using [`encodeURIComponent`](#encode-and-decode) otherwise.
 
 ### cookie.parseSetCookie(str, options)
 
@@ -88,7 +88,7 @@ const setCookieHeader = cookie.stringifySetCookie({
 
 #### Options
 
-- `encode` Specifies the function to encode a [cookie-value](https://datatracker.ietf.org/doc/html/rfc6265#section-4.1.1). Defaults to preserving valid cookie-octet values and using [`encodeURIComponent`](#encode-and-decode) otherwise.
+- `encode` Specifies the function to encode a [cookie-value](https://datatracker.ietf.org/doc/html/rfc6265#section-4.1.1). Defaults to preserving roundtrip-safe cookie-octet values and using [`encodeURIComponent`](#encode-and-decode) otherwise.
 
 ## Cookie object
 
@@ -178,7 +178,7 @@ More information about enforcement levels can be found in [the specification](ht
 Cookie accepts `encode` or `decode` options for processing a [cookie-value](https://datatracker.ietf.org/doc/html/rfc6265#section-4.1.1).
 Since the value of a cookie has a limited character set (and must be a simple string), these functions are used to transform values into strings suitable for a cookies value.
 
-The default `encode` function preserves valid RFC 6265 cookie-octet values and uses the global `encodeURIComponent` otherwise.
+The default `encode` function preserves roundtrip-safe cookie-octet values and uses the global `encodeURIComponent` otherwise.
 
 The default `decode` function is the global `decodeURIComponent`, wrapped in a `try..catch`. If an error
 is thrown it will return the cookie's original value. If you provide your own encode/decode
diff --git a/src/index.ts b/src/index.ts
index 169953b..33ce704 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -69,9 +69,9 @@ const pathValueRegExp = /^[\u0020-\u003A\u003D-\u007E]*$/;
 const maxAgeRegExp = /^-?\d+$/;
 
 /**
- * RegExp to match RFC 6265 cookie-octet values that need no URL encoding.
+ * RegExp to match RFC 6265 cookie-octet values (without % to preserve round-trip) that need no URL encoding.
  */
-const cookieOctetRegExp = /^[!#$%&'()*+\-.\/0-9:<=>?@A-Z[\]\^_`a-z{|}~]*$/;
+const cookieOctetRegExp = /^[!#$&'()*+\-.\/0-9:<=>?@A-Z[\]\^_`a-z{|}~]*$/;
 
 const __toString = Object.prototype.toString;
 
@@ -149,7 +149,7 @@ export interface StringifyOptions {
    * Specifies a function that will be used to encode a [cookie-value](https://datatracker.ietf.org/doc/html/rfc6265#section-4.1.1).
    * Since value of a cookie has a limited character set (and must be a simple string), this function can be used to encode
    * a value into a string suited for a cookie's value, and should mirror `decode` when parsing.
-   * The default function preserves valid RFC 6265 cookie-octet values and uses `encodeURIComponent` otherwise.
+   * The default function preserves roundtrip-safe cookie-octet values and uses `encodeURIComponent` otherwise.
    *
    * @default encode
    */
@@ -541,7 +541,7 @@ function decode(str: string): string {
 }
 
 /**
- * URL-encode string value. Optimized to skip native call for RFC 6265 cookie-octet values.
+ * URL-encode string value. Optimized to skip native call for roundtrip-safe cookie-octet values.
  */
 function encode(str: string): string {
   return cookieOctetRegExp.test(str) ? str : encodeURIComponent(str);
diff --git a/src/stringify-cookie.bench.ts b/src/stringify-cookie.bench.ts
index a882aaf..f078ab7 100644
--- a/src/stringify-cookie.bench.ts
+++ b/src/stringify-cookie.bench.ts
@@ -11,7 +11,7 @@ describe("cookie.stringifyCookie", () => {
   });
 
   bench("rfc cookie-octets", () => {
-    cookie.stringifyCookie({ foo: "a=b+c/d?x%20" });
+    cookie.stringifyCookie({ foo: "a=b+c/d?x~" });
   });
 
   bench("encode", () => {
diff --git a/src/stringify-cookie.spec.ts b/src/stringify-cookie.spec.ts
index 11f89fa..ac310f9 100644
--- a/src/stringify-cookie.spec.ts
+++ b/src/stringify-cookie.spec.ts
@@ -38,22 +38,25 @@ describe("cookie.stringifyCookie", () => {
     );
     expect(stringifyCookie({ foo: "foo,bar" })).toEqual("foo=foo%2Cbar");
     expect(stringifyCookie({ foo: "foo\\bar" })).toEqual("foo=foo%5Cbar");
+    expect(stringifyCookie({ foo: "100%" })).toEqual("foo=100%25");
   });
 
-  it("should pass through cookie-octet values by default", () => {
+  it("should pass through roundtrip-safe cookie-octet values without encoding", () => {
     const value =
-      "!#$%&'()*+-./0123456789:<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[]" +
+      "!#$&'()*+-./0123456789:<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[]" +
       "^_`abcdefghijklmnopqrstuvwxyz{|}~";
 
     expect(stringifyCookie({ foo: value })).toEqual(`foo=${value}`);
   });
 
-  it("should match cookie-octet default encoding", () => {
+  it("should match default encoding for all valid BMP characters", () => {
     const cookieOctets =
-      "!#$%&'()*+-./0123456789:<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[]" +
+      "!#$&'()*+-./0123456789:<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[]" +
       "^_`abcdefghijklmnopqrstuvwxyz{|}~";
     const mismatches: string[] = [];
 
+    // Check every valid BMP character. Skip surrogate code units because
+    // encodeURIComponent throws on unpaired surrogates.
     for (let code = 0; code <= 0xffff; code++) {
       if (code >= 0xd800 && code <= 0xdfff) continue;
 
@@ -159,6 +162,14 @@ describe("cookie.stringifyCookie", () => {
       expect(parseCookie(str)).toEqual(cookies);
     });
 
+    it("should roundtrip percent-encoded-looking values", () => {
+      const cookies = { foo: "%20" };
+      const str = stringifyCookie(cookies);
+
+      expect(str).toEqual("foo=%2520");
+      expect(parseCookie(str)).toEqual(cookies);
+    });
+
     it("should roundtrip empty values", () => {
       const cookies = { a: "", b: "value" };
       const str = stringifyCookie(cookies);
diff --git a/src/stringify-set-cookie.spec.ts b/src/stringify-set-cookie.spec.ts
index 3b718f2..b33c329 100644
--- a/src/stringify-set-cookie.spec.ts
+++ b/src/stringify-set-cookie.spec.ts
@@ -16,9 +16,9 @@ describe("cookie.stringifySetCookie", function () {
     );
   });
 
-  it("should pass through cookie-octet values", function () {
+  it("should pass through roundtrip-safe cookie-octet values without encoding", function () {
     const value =
-      "!#$%&'()*+-./0123456789:<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[]" +
+      "!#$&'()*+-./0123456789:<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[]" +
       "^_`abcdefghijklmnopqrstuvwxyz{|}~";
 
     expect(cookie.stringifySetCookie("foo", value)).toEqual(`foo=${value}`);

From d7b2a910bd0145947774005b04a6231aaf730ae3 Mon Sep 17 00:00:00 2001
From: saripovdenis <iam.saripov.denis@gmail.com>
Date: Tue, 12 May 2026 01:12:09 +0800
Subject: [PATCH 07/12] test: add % test to stringifySetCookie

---
 src/stringify-set-cookie.spec.ts | 1 +
 1 file changed, 1 insertion(+)

diff --git a/src/stringify-set-cookie.spec.ts b/src/stringify-set-cookie.spec.ts
index b33c329..68d7d61 100644
--- a/src/stringify-set-cookie.spec.ts
+++ b/src/stringify-set-cookie.spec.ts
@@ -14,6 +14,7 @@ describe("cookie.stringifySetCookie", function () {
     expect(cookie.stringifySetCookie("foo", "bar +baz")).toEqual(
       "foo=bar%20%2Bbaz",
     );
+    expect(cookie.stringifySetCookie("foo", "100%")).toEqual("foo=100%25");
   });
 
   it("should pass through roundtrip-safe cookie-octet values without encoding", function () {

From 9d327b0df7ec3e92ff45a8881c3a7d468f7c12b4 Mon Sep 17 00:00:00 2001
From: saripovdenis <iam.saripov.denis@gmail.com>
Date: Fri, 15 May 2026 00:11:53 +0800
Subject: [PATCH 08/12] doc: revert stringifyCookie and stringifySetCookie
 readme

---
 README.md | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/README.md b/README.md
index 1182c2a..74f4b29 100644
--- a/README.md
+++ b/README.md
@@ -48,7 +48,7 @@ const cookieHeader = cookie.stringifyCookie({ a: "foo", b: "bar" });
 
 #### Options
 
-- `encode` Specifies the function to encode a [cookie-value](https://datatracker.ietf.org/doc/html/rfc6265#section-4.1.1). Defaults to preserving roundtrip-safe cookie-octet values and using [`encodeURIComponent`](#encode-and-decode) otherwise.
+- `encode` Specifies the function to encode a [cookie-value](https://datatracker.ietf.org/doc/html/rfc6265#section-4.1.1). Defaults to [`encodeURIComponent`](#encode-and-decode).
 
 ### cookie.parseSetCookie(str, options)
 
@@ -88,7 +88,7 @@ const setCookieHeader = cookie.stringifySetCookie({
 
 #### Options
 
-- `encode` Specifies the function to encode a [cookie-value](https://datatracker.ietf.org/doc/html/rfc6265#section-4.1.1). Defaults to preserving roundtrip-safe cookie-octet values and using [`encodeURIComponent`](#encode-and-decode) otherwise.
+- `encode` Specifies the function to encode a [cookie-value](https://datatracker.ietf.org/doc/html/rfc6265#section-4.1.1). Defaults to [`encodeURIComponent`](#encode-and-decode).
 
 ## Cookie object
 

From 17e7c75f59b8bbeb270ec05e26c059410418df4d Mon Sep 17 00:00:00 2001
From: saripovdenis <iam.saripov.denis@gmail.com>
Date: Sun, 17 May 2026 16:02:04 +0800
Subject: [PATCH 09/12] chore: clean up tests

---
 src/stringify-cookie.spec.ts | 83 ++++++++++++++++++++----------------
 1 file changed, 46 insertions(+), 37 deletions(-)

diff --git a/src/stringify-cookie.spec.ts b/src/stringify-cookie.spec.ts
index ac310f9..f372978 100644
--- a/src/stringify-cookie.spec.ts
+++ b/src/stringify-cookie.spec.ts
@@ -1,6 +1,38 @@
 import { describe, expect, it } from "vitest";
 import { stringifyCookie, parseCookie } from "./index.js";
 
+const roundtripSafeCookieOctets =
+  "!#$&'()*+-./0123456789:<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[]" +
+  "^_`abcdefghijklmnopqrstuvwxyz{|}~";
+
+const defaultBmpEncodingCases: Array<[string, string, string]> = [];
+
+for (let code = 0; code <= 0xffff; code++) {
+  // encodeURIComponent throws on unpaired surrogates.
+  if (code >= 0xd800 && code <= 0xdfff) continue;
+
+  const value = String.fromCharCode(code);
+  const encoded = roundtripSafeCookieOctets.includes(value)
+    ? value
+    : encodeURIComponent(value);
+
+  defaultBmpEncodingCases.push([
+    `U+${code.toString(16).toUpperCase().padStart(4, "0")}`,
+    value,
+    `key=${encoded}`,
+  ]);
+}
+
+const defaultAstralEncodingCases: Array<[string, string, string]> = [];
+
+for (const value of ["😄", "𝌆", "𠜎"]) {
+  defaultAstralEncodingCases.push([
+    `U+${value.codePointAt(0)!.toString(16).toUpperCase()}`,
+    value,
+    `key=${encodeURIComponent(value)}`,
+  ]);
+}
+
 describe("cookie.stringifyCookie", () => {
   it("should stringify object", () => {
     expect(stringifyCookie({ key: "value" })).toEqual("key=value");
@@ -42,47 +74,24 @@ describe("cookie.stringifyCookie", () => {
   });
 
   it("should pass through roundtrip-safe cookie-octet values without encoding", () => {
-    const value =
-      "!#$&'()*+-./0123456789:<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[]" +
-      "^_`abcdefghijklmnopqrstuvwxyz{|}~";
+    const value = roundtripSafeCookieOctets;
 
     expect(stringifyCookie({ foo: value })).toEqual(`foo=${value}`);
   });
 
-  it("should match default encoding for all valid BMP characters", () => {
-    const cookieOctets =
-      "!#$&'()*+-./0123456789:<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[]" +
-      "^_`abcdefghijklmnopqrstuvwxyz{|}~";
-    const mismatches: string[] = [];
-
-    // Check every valid BMP character. Skip surrogate code units because
-    // encodeURIComponent throws on unpaired surrogates.
-    for (let code = 0; code <= 0xffff; code++) {
-      if (code >= 0xd800 && code <= 0xdfff) continue;
-
-      const value = String.fromCharCode(code);
-      const actual = stringifyCookie({ key: value });
-      const encoded = cookieOctets.includes(value)
-        ? value
-        : encodeURIComponent(value);
-      const expected = `key=${encoded}`;
-
-      if (actual !== expected) {
-        mismatches.push(`${code}: ${actual} !== ${expected}`);
-      }
-    }
-
-    for (const value of ["😄", "𝌆", "𠜎"]) {
-      const actual = stringifyCookie({ key: value });
-      const expected = `key=${encodeURIComponent(value)}`;
-
-      if (actual !== expected) {
-        mismatches.push(`${value}: ${actual} !== ${expected}`);
-      }
-    }
-
-    expect(mismatches).toEqual([]);
-  });
+  it.each(defaultBmpEncodingCases)(
+    "should match default encoding for BMP char %s",
+    (_name, value, expected) => {
+      expect(stringifyCookie({ key: value })).toEqual(expected);
+    },
+  );
+
+  it.each(defaultAstralEncodingCases)(
+    "should match default encoding for astral char %s",
+    (_name, value, expected) => {
+      expect(stringifyCookie({ key: value })).toEqual(expected);
+    },
+  );
 
   it("should error on invalid keys", () => {
     expect(() => stringifyCookie({ "test=": "" })).toThrow(

From c07a99025bd3e87786362502ac31d05fd9fe6fa4 Mon Sep 17 00:00:00 2001
From: saripovdenis <iam.saripov.denis@gmail.com>
Date: Sun, 17 May 2026 16:19:55 +0800
Subject: [PATCH 10/12] chore: polish encode docs and tests

---
 src/index.ts                     | 10 ++++------
 src/stringify-set-cookie.spec.ts |  8 +++++---
 2 files changed, 9 insertions(+), 9 deletions(-)

diff --git a/src/index.ts b/src/index.ts
index 33ce704..b2f233e 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -69,7 +69,7 @@ const pathValueRegExp = /^[\u0020-\u003A\u003D-\u007E]*$/;
 const maxAgeRegExp = /^-?\d+$/;
 
 /**
- * RegExp to match RFC 6265 cookie-octet values (without % to preserve round-trip) that need no URL encoding.
+ * RegExp to match RFC 6265 cookie-octet values (without % to preserve roundtrip) that need no URL encoding.
  */
 const cookieOctetRegExp = /^[!#$&'()*+\-.\/0-9:<=>?@A-Z[\]\^_`a-z{|}~]*$/;
 
@@ -150,8 +150,6 @@ export interface StringifyOptions {
    * Since value of a cookie has a limited character set (and must be a simple string), this function can be used to encode
    * a value into a string suited for a cookie's value, and should mirror `decode` when parsing.
    * The default function preserves roundtrip-safe cookie-octet values and uses `encodeURIComponent` otherwise.
-   *
-   * @default encode
    */
   encode?: (str: string) => string;
 }
@@ -163,7 +161,7 @@ export function stringifyCookie(
   cookie: Cookies,
   options?: StringifyOptions,
 ): string {
-  const enc = options?.encode || encode;
+  const enc = options?.encode || defaultEncode;
   const keys = Object.keys(cookie);
   let str = "";
 
@@ -304,7 +302,7 @@ export function stringifySetCookie(
       ? _name
       : { ..._opts, name: _name, value: String(_val) };
   const options = typeof _val === "object" ? _val : _opts;
-  const enc = options?.encode || encode;
+  const enc = options?.encode || defaultEncode;
 
   if (!cookieNameRegExp.test(cookie.name)) {
     throw new TypeError(`argument name is invalid: ${cookie.name}`);
@@ -543,7 +541,7 @@ function decode(str: string): string {
 /**
  * URL-encode string value. Optimized to skip native call for roundtrip-safe cookie-octet values.
  */
-function encode(str: string): string {
+function defaultEncode(str: string): string {
   return cookieOctetRegExp.test(str) ? str : encodeURIComponent(str);
 }
 
diff --git a/src/stringify-set-cookie.spec.ts b/src/stringify-set-cookie.spec.ts
index 68d7d61..04e5780 100644
--- a/src/stringify-set-cookie.spec.ts
+++ b/src/stringify-set-cookie.spec.ts
@@ -1,6 +1,10 @@
 import { describe, it, expect } from "vitest";
 import * as cookie from "./index.js";
 
+const roundtripSafeCookieOctets =
+  "!#$&'()*+-./0123456789:<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[]" +
+  "^_`abcdefghijklmnopqrstuvwxyz{|}~";
+
 describe("cookie.stringifySetCookie", function () {
   it("should have backward compatible export", function () {
     expect(cookie.serialize).toBe(cookie.stringifySetCookie);
@@ -18,9 +22,7 @@ describe("cookie.stringifySetCookie", function () {
   });
 
   it("should pass through roundtrip-safe cookie-octet values without encoding", function () {
-    const value =
-      "!#$&'()*+-./0123456789:<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[]" +
-      "^_`abcdefghijklmnopqrstuvwxyz{|}~";
+    const value = roundtripSafeCookieOctets;
 
     expect(cookie.stringifySetCookie("foo", value)).toEqual(`foo=${value}`);
   });

From 6451a64bc40837c1e5ea0a4f808e480c94ddc83f Mon Sep 17 00:00:00 2001
From: saripovdenis <iam.saripov.denis@gmail.com>
Date: Sun, 17 May 2026 16:27:33 +0800
Subject: [PATCH 11/12] chore: rename test constants

---
 src/stringify-cookie.spec.ts     | 18 +++++++++---------
 src/stringify-set-cookie.spec.ts |  4 ++--
 2 files changed, 11 insertions(+), 11 deletions(-)

diff --git a/src/stringify-cookie.spec.ts b/src/stringify-cookie.spec.ts
index f372978..84ca554 100644
--- a/src/stringify-cookie.spec.ts
+++ b/src/stringify-cookie.spec.ts
@@ -1,32 +1,32 @@
 import { describe, expect, it } from "vitest";
 import { stringifyCookie, parseCookie } from "./index.js";
 
-const roundtripSafeCookieOctets =
+const cookieOctets =
   "!#$&'()*+-./0123456789:<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[]" +
   "^_`abcdefghijklmnopqrstuvwxyz{|}~";
 
-const defaultBmpEncodingCases: Array<[string, string, string]> = [];
+const bmpEncodingCases: Array<[string, string, string]> = [];
 
 for (let code = 0; code <= 0xffff; code++) {
   // encodeURIComponent throws on unpaired surrogates.
   if (code >= 0xd800 && code <= 0xdfff) continue;
 
   const value = String.fromCharCode(code);
-  const encoded = roundtripSafeCookieOctets.includes(value)
+  const encoded = cookieOctets.includes(value)
     ? value
     : encodeURIComponent(value);
 
-  defaultBmpEncodingCases.push([
+  bmpEncodingCases.push([
     `U+${code.toString(16).toUpperCase().padStart(4, "0")}`,
     value,
     `key=${encoded}`,
   ]);
 }
 
-const defaultAstralEncodingCases: Array<[string, string, string]> = [];
+const astralEncodingCases: Array<[string, string, string]> = [];
 
 for (const value of ["😄", "𝌆", "𠜎"]) {
-  defaultAstralEncodingCases.push([
+  astralEncodingCases.push([
     `U+${value.codePointAt(0)!.toString(16).toUpperCase()}`,
     value,
     `key=${encodeURIComponent(value)}`,
@@ -74,19 +74,19 @@ describe("cookie.stringifyCookie", () => {
   });
 
   it("should pass through roundtrip-safe cookie-octet values without encoding", () => {
-    const value = roundtripSafeCookieOctets;
+    const value = cookieOctets;
 
     expect(stringifyCookie({ foo: value })).toEqual(`foo=${value}`);
   });
 
-  it.each(defaultBmpEncodingCases)(
+  it.each(bmpEncodingCases)(
     "should match default encoding for BMP char %s",
     (_name, value, expected) => {
       expect(stringifyCookie({ key: value })).toEqual(expected);
     },
   );
 
-  it.each(defaultAstralEncodingCases)(
+  it.each(astralEncodingCases)(
     "should match default encoding for astral char %s",
     (_name, value, expected) => {
       expect(stringifyCookie({ key: value })).toEqual(expected);
diff --git a/src/stringify-set-cookie.spec.ts b/src/stringify-set-cookie.spec.ts
index 04e5780..e9c2983 100644
--- a/src/stringify-set-cookie.spec.ts
+++ b/src/stringify-set-cookie.spec.ts
@@ -1,7 +1,7 @@
 import { describe, it, expect } from "vitest";
 import * as cookie from "./index.js";
 
-const roundtripSafeCookieOctets =
+const cookieOctets =
   "!#$&'()*+-./0123456789:<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[]" +
   "^_`abcdefghijklmnopqrstuvwxyz{|}~";
 
@@ -22,7 +22,7 @@ describe("cookie.stringifySetCookie", function () {
   });
 
   it("should pass through roundtrip-safe cookie-octet values without encoding", function () {
-    const value = roundtripSafeCookieOctets;
+    const value = cookieOctets;
 
     expect(cookie.stringifySetCookie("foo", value)).toEqual(`foo=${value}`);
   });

From 4a41e824c74706b39c0b8c5acbcdb6d94de49ad9 Mon Sep 17 00:00:00 2001
From: saripovdenis <iam.saripov.denis@gmail.com>
Date: Sun, 17 May 2026 16:43:09 +0800
Subject: [PATCH 12/12] chore: simplify astral encoding cases

---
 src/stringify-cookie.spec.ts | 18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/src/stringify-cookie.spec.ts b/src/stringify-cookie.spec.ts
index 84ca554..0e4c634 100644
--- a/src/stringify-cookie.spec.ts
+++ b/src/stringify-cookie.spec.ts
@@ -23,15 +23,15 @@ for (let code = 0; code <= 0xffff; code++) {
   ]);
 }
 
-const astralEncodingCases: Array<[string, string, string]> = [];
-
-for (const value of ["😄", "𝌆", "𠜎"]) {
-  astralEncodingCases.push([
-    `U+${value.codePointAt(0)!.toString(16).toUpperCase()}`,
-    value,
-    `key=${encodeURIComponent(value)}`,
-  ]);
-}
+const astralEncodingCases: Array<[string, string, string]> = [
+  "😄",
+  "𝌆",
+  "𠜎",
+].map((value) => [
+  `U+${value.codePointAt(0)!.toString(16).toUpperCase()}`,
+  value,
+  `key=${encodeURIComponent(value)}`,
+]);
 
 describe("cookie.stringifyCookie", () => {
   it("should stringify object", () => {