diff --git a/psf-memo-db/util/post/backfill-post-heights.js b/psf-memo-db/util/post/backfill-post-heights.js
new file mode 100644
index 0000000..35a2c99
--- /dev/null
+++ b/psf-memo-db/util/post/backfill-post-heights.js
@@ -0,0 +1,132 @@
+/*
+  Utility: backfill the postHeights secondary index for an existing psf-memo-db.
+
+  The postHeights index is required for efficient pagination of /posts/recent and
+  /posts/by/:addr. New deployments write this index while indexing live blocks,
+  but existing databases that were populated before the postHeights feature need
+  a one-time backfill.
+
+  Run from the psf-memo-db repo root on the host that owns the LevelDB files:
+
+    node util/post/backfill-post-heights.js
+
+  The script is idempotent: re-running it will not create duplicate index
+  entries. Progress and a summary are printed to stderr.
+
+  WARNING:
+  - This script opens the LevelDB files directly. psf-memo-db must NOT be
+    running, or another process must not hold the database locks.
+  - Make a backup of leveldb/current before running on a production server:
+      cp -r leveldb/current leveldb/current-pre-postheights-backup
+*/
+
+import level from 'level'
+import * as fs from 'fs'
+import * as path from 'path'
+import * as url from 'url'
+
+const __dirname = url.fileURLToPath(new URL('.', import.meta.url))
+
+const DATA_DIR = process.env.PSF_MEMO_DB_DATA_DIR
+  ? path.resolve(process.env.PSF_MEMO_DB_DATA_DIR)
+  : path.resolve(__dirname, '../../leveldb/current')
+
+const HEIGHT_PAD = 12
+const PROGRESS_INTERVAL = 10000
+
+function requiredStorePath (dir, name) {
+  const storePath = path.join(dir, name)
+  if (!fs.existsSync(storePath)) {
+    throw new Error(`Required LevelDB store not found: ${storePath}. Set PSF_MEMO_DB_DATA_DIR to the directory containing the posts, postHeights, and postParents stores.`)
+  }
+  return storePath
+}
+
+function postHeightKey (blockHeight, txid) {
+  const padded = String(blockHeight).padStart(HEIGHT_PAD, '0')
+  return `${padded}:${txid}`
+}
+
+async function createIfMissing (db, key, value) {
+  try {
+    await db.get(key)
+    return false
+  } catch (err) {
+    if (err.notFound || err.code === 'LEVEL_NOT_FOUND') {
+      await db.put(key, value)
+      return true
+    }
+    throw err
+  }
+}
+
+async function backfill () {
+  console.error(`Using LevelDB data directory: ${DATA_DIR}`)
+
+  const postsPath = requiredStorePath(DATA_DIR, 'posts')
+  const postParentsPath = requiredStorePath(DATA_DIR, 'postParents')
+  const postHeightsPath = path.join(DATA_DIR, 'postHeights')
+
+  console.error('Opening LevelDB stores...')
+  const postsDb = level(postsPath, { valueEncoding: 'json' })
+  const postHeightsDb = level(postHeightsPath, { valueEncoding: 'json', createIfMissing: true })
+  const postParentsDb = level(postParentsPath, { valueEncoding: 'json' })
+
+  try {
+    console.error('Loading reply txids from postParents...')
+    const replyTxids = new Set()
+    let replyCount = 0
+    for await (const [childTxid] of postParentsDb.iterator()) {
+      replyTxids.add(childTxid)
+      replyCount++
+    }
+    console.error(`Loaded ${replyCount} reply txids.`)
+
+    console.error('Scanning posts and backfilling postHeights entries...')
+    let postsScanned = 0
+    let topLevelPosts = 0
+    let indexEntriesCreated = 0
+    let indexEntriesExisting = 0
+
+    for await (const [txid, post] of postsDb.iterator()) {
+      postsScanned++
+
+      if (replyTxids.has(txid)) {
+        if (postsScanned % PROGRESS_INTERVAL === 0) {
+          console.error(`  scanned ${postsScanned} posts, ${topLevelPosts} top-level, ${indexEntriesCreated} written, ${indexEntriesExisting} skipped...`)
+        }
+        continue
+      }
+
+      topLevelPosts++
+      const blockHeight = post.blockHeight ?? 0
+      const key = postHeightKey(blockHeight, txid)
+      const value = { txid, blockHeight }
+      const created = await createIfMissing(postHeightsDb, key, value)
+      if (created) {
+        indexEntriesCreated++
+      } else {
+        indexEntriesExisting++
+      }
+
+      if (postsScanned % PROGRESS_INTERVAL === 0) {
+        console.error(`  scanned ${postsScanned} posts, ${topLevelPosts} top-level, ${indexEntriesCreated} written, ${indexEntriesExisting} skipped...`)
+      }
+    }
+
+    console.error('\nBackfill complete.')
+    console.error(`  posts scanned:        ${postsScanned}`)
+    console.error(`  top-level posts:      ${topLevelPosts}`)
+    console.error(`  index entries created: ${indexEntriesCreated}`)
+    console.error(`  index entries already present: ${indexEntriesExisting}`)
+  } catch (err) {
+    console.error('\nBackfill failed:', err.message)
+    process.exitCode = 1
+  } finally {
+    await postHeightsDb.close().catch(() => {})
+    await postParentsDb.close().catch(() => {})
+    await postsDb.close().catch(() => {})
+  }
+}
+
+backfill()