diff --git a/28.md b/28.md
new file mode 100644
index 000000000..43c598abc
--- /dev/null
+++ b/28.md
@@ -0,0 +1,93 @@
+# NUT-28: Mint Quote Lookup by Public Key
+
+`optional`
+
+`depends on: NUT-04, NUT-20`
+
+---
+
+This NUT adds an endpoint for users to query mint quotes associated with their public key. This enables third-party mint quotes where one user creates and pays a quote for another user to redeem.
+
+> [!NOTE]
+>
+> Quote creation with a public key and minting with a signature are defined in [NUT-20][20]. This NUT only adds the ability to discover quotes by public key.
+
+## Use cases
+
+- **Mining pools**: A pool creates paid quotes for miners' public keys when shares are validated
+- **Gift payments**: `Alice` pays for `Bob` to receive ecash without `Bob` initiating a request
+
+## Querying quotes by public key
+
+To query quotes assigned to a public key, the wallet makes a `POST /v1/mint/quote/{method}/pubkey` request.
+
+```http
+POST https://mint.host:3338/v1/mint/quote/bolt11/pubkey
+```
+
+The wallet includes the following `PostMintQuotesByPubkeyRequest` data:
+
+```json
+{
+  "pubkey": <str>,
+  "timestamp": <int>,
+  "signature": <str>,
+  "unit": <str|null>,
+  "state": <str|null>
+}
+```
+
+| Field | Type | Description |
+| --- | --- | --- |
+| `pubkey` | `str` | Compressed secp256k1 public key (33 bytes, hex-encoded) |
+| `timestamp` | `int` | Unix timestamp (provides entropy for signature) |
+| `signature` | `str` | BIP340 Schnorr signature (see below) |
+| `unit` | `str\|null` | Optional filter by currency unit |
+| `state` | `str\|null` | Optional filter by quote state |
+
+### Signature scheme
+
+The message to sign is:
+
+```
+msg_to_sign = "quote_lookup" || pubkey || timestamp || unit || state
+```
+
+Where `||` denotes concatenation. All fields are UTF-8 strings. If `unit` or `state` is null, use an empty string.
+
+The signature is a [BIP340](https://github.com/bitcoin/bips/blob/master/bip-0340.mediawiki) Schnorr signature on `SHA256(msg_to_sign)`.
+
+### Response
+
+The mint responds with a `PostMintQuotesByPubkeyResponse`:
+
+```json
+{
+  "quotes": <Array[MintQuoteResponse]>
+}
+```
+
+Where `MintQuoteResponse` is the quote response type defined in [NUT-04][04].
+
+## Errors
+
+See [Error Codes][errors]:
+
+- `20010`: Signature for quote lookup invalid
+
+## Settings
+
+The settings for this NUT are part of the mint info response ([NUT-06][06]):
+
+```json
+{
+  "28": {
+    "supported": <bool>
+  }
+}
+```
+
+[04]: 04.md
+[06]: 06.md
+[20]: 20.md
+[errors]: error_codes.md
diff --git a/README.md b/README.md
index 60d2f47ab..18aa6e6ab 100644
--- a/README.md
+++ b/README.md
@@ -43,6 +43,7 @@ Wallets and mints `MUST` implement all mandatory specs and `CAN` implement optio
 | [25][25] | Payment Method: BOLT12            | [cdk], [cashu-ts][ts]                                                          | [cdk-mintd]                                      |
 | [26][26] | Payment Request Bech32m Encoding  | [cdk]                                                                          | -                                                |
 | [27][27] | Nostr Mint Backup                 | [Cashu.me][cashume], [cdk]                                                     | -                                                |
+| [28][28] | Third-Party Mint Quotes           | -                                                                              | -                                                |
 
 #### Wallets:
 
@@ -102,3 +103,4 @@ Wallets and mints `MUST` implement all mandatory specs and `CAN` implement optio
 [25]: 25.md
 [26]: 26.md
 [27]: 27.md
+[28]: 28.md
diff --git a/error_codes.md b/error_codes.md
index e3fdfb9f3..989d93613 100644
--- a/error_codes.md
+++ b/error_codes.md
@@ -27,6 +27,7 @@
 | 20007 | Quote is expired                                | [NUT-04][04], [NUT-05][05]               |
 | 20008 | Signature for mint request invalid              | [NUT-20][20]                             |
 | 20009 | Pubkey required for mint quote                  | [NUT-20][20]                             |
+| 20010 | Signature for quote lookup invalid              | [NUT-28][28]                             |
 | 30001 | Endpoint requires clear auth                    | [NUT-21][21]                             |
 | 30002 | Clear authentication failed                     | [NUT-21][21]                             |
 | 31001 | Endpoint requires blind auth                    | [NUT-22][22]                             |
@@ -50,3 +51,4 @@
 [20]: 20.md
 [21]: 21.md
 [22]: 22.md
+[28]: 28.md
diff --git a/tests/28-test.md b/tests/28-test.md
new file mode 100644
index 000000000..a921cada8
--- /dev/null
+++ b/tests/28-test.md
@@ -0,0 +1,33 @@
+# NUT-28 Test Vectors
+
+## Quote Lookup Signature
+
+### Message Construction
+
+For a request with:
+- `pubkey` = `03d56ce4e446a85bbdaa547b4ec2b073d40ff802831352b8272b7dd7a4de5a7cac`
+- `timestamp` = `1701704800`
+- `unit` = `sat`
+- `state` = `PAID`
+
+```
+msg_to_sign = "quote_lookup" || pubkey || timestamp || unit || state
+            = "quote_lookup03d56ce4e446a85bbdaa547b4ec2b073d40ff802831352b8272b7dd7a4de5a7cac1701704800satPAID"
+```
+
+For a request with null filters:
+- `pubkey` = `03d56ce4e446a85bbdaa547b4ec2b073d40ff802831352b8272b7dd7a4de5a7cac`
+- `timestamp` = `1701704800`
+- `unit` = null
+- `state` = null
+
+```
+msg_to_sign = "quote_lookup" || pubkey || timestamp || "" || ""
+            = "quote_lookup03d56ce4e446a85bbdaa547b4ec2b073d40ff802831352b8272b7dd7a4de5a7cac1701704800"
+```
+
+The signature is BIP340 Schnorr on `SHA256(msg_to_sign)`.
+
+### Invalid Signature
+
+A request with an invalid signature should return error code `20010`.