diff --git a/nip13.test.ts b/nip13.test.ts
index 281f5cc..7c4a805 100644
--- a/nip13.test.ts
+++ b/nip13.test.ts
@@ -2,9 +2,14 @@ import { test, expect } from 'bun:test'
 import { getPow, minePow } from './nip13.ts'
 
 test('identifies proof-of-work difficulty', async () => {
-  const id = '000006d8c378af1779d2feebc7603a125d99eca0ccf1085959b307f64e5dd358'
-  const difficulty = getPow(id)
-  expect(difficulty).toEqual(21)
+  ;[
+    ['000006d8c378af1779d2feebc7603a125d99eca0ccf1085959b307f64e5dd358', 21],
+    ['6bf5b4f434813c64b523d2b0e6efe18f3bd0cbbd0a5effd8ece9e00fd2531996', 1],
+    ['00003479309ecdb46b1c04ce129d2709378518588bed6776e60474ebde3159ae', 18],
+    ['01a76167d41add96be4959d9e618b7a35f26551d62c43c11e5e64094c6b53c83', 7],
+    ['ac4f44bae06a45ebe88cfbd3c66358750159650a26c0d79e8ccaa92457fca4f6', 0],
+    ['0000000000000000006cfbd3c66358750159650a26c0d79e8ccaa92457fca4f6', 73],
+  ].forEach(([id, diff]) => expect(getPow(id as string)).toEqual(diff as number))
 })
 
 test('mines POW for an event', async () => {
diff --git a/nip13.ts b/nip13.ts
index 8f1bfc2..45003a7 100644
--- a/nip13.ts
+++ b/nip13.ts
@@ -1,15 +1,19 @@
-import { type UnsignedEvent, type Event, getEventHash } from './pure.ts'
+import { bytesToHex } from '@noble/hashes/utils'
+import { type UnsignedEvent, type Event } from './pure.ts'
+import { sha256 } from '@noble/hashes/sha256'
+
+import { utf8Encoder } from './utils.ts'
 
 /** Get POW difficulty from a Nostr hex ID. */
 export function getPow(hex: string): number {
   let count = 0
 
-  for (let i = 0; i < hex.length; i++) {
-    const nibble = parseInt(hex[i], 16)
+  for (let i = 0; i < 64; i += 8) {
+    const nibble = parseInt(hex.substring(i, i + 8), 16)
     if (nibble === 0) {
-      count += 4
+      count += 32
     } else {
-      count += Math.clz32(nibble) - 28
+      count += Math.clz32(nibble)
       break
     }
   }
@@ -20,8 +24,6 @@ export function getPow(hex: string): number {
 /**
  * Mine an event with the desired POW. This function mutates the event.
  * Note that this operation is synchronous and should be run in a worker context to avoid blocking the main thread.
- *
- * Adapted from Snort: https://git.v0l.io/Kieran/snort/src/commit/4df6c19248184218c4c03728d61e94dae5f2d90c/packages/system/src/pow-util.ts#L14-L36
  */
 export function minePow(unsigned: UnsignedEvent, difficulty: number): Omit<Event, 'sig'> {
   let count = 0
@@ -41,7 +43,7 @@ export function minePow(unsigned: UnsignedEvent, difficulty: number): Omit<Event
 
     tag[1] = (++count).toString()
 
-    event.id = getEventHash(event)
+    event.id = fastEventHash(event)
 
     if (getPow(event.id) >= difficulty) {
       break
@@ -50,3 +52,9 @@ export function minePow(unsigned: UnsignedEvent, difficulty: number): Omit<Event
 
   return event
 }
+
+export function fastEventHash(evt: UnsignedEvent): string {
+  return bytesToHex(
+    sha256(utf8Encoder.encode(JSON.stringify([0, evt.pubkey, evt.created_at, evt.kind, evt.tags, evt.content]))),
+  )
+}