diff --git a/src/RelayError.ts b/src/RelayError.ts
new file mode 100644
index 0000000..1d275f6
--- /dev/null
+++ b/src/RelayError.ts
@@ -0,0 +1,24 @@
+import { NostrRelayOK } from '@nostrify/nostrify';
+
+export type RelayErrorPrefix = 'duplicate' | 'pow' | 'blocked' | 'rate-limited' | 'invalid' | 'error';
+
+/** NIP-01 command line result. */
+export class RelayError extends Error {
+  constructor(prefix: RelayErrorPrefix, message: string) {
+    super(`${prefix}: ${message}`);
+  }
+
+  /** Construct a RelayError from the reason message. */
+  static fromReason(reason: string): RelayError {
+    const [prefix, ...rest] = reason.split(': ');
+    return new RelayError(prefix as RelayErrorPrefix, rest.join(': '));
+  }
+
+  /** Throw a new RelayError if the OK message is false. */
+  static assert(msg: NostrRelayOK): void {
+    const [_, _eventId, ok, reason] = msg;
+    if (!ok) {
+      throw RelayError.fromReason(reason);
+    }
+  }
+}
diff --git a/src/controllers/nostr/relay.ts b/src/controllers/nostr/relay.ts
index 7d70ad9..c0fa026 100644
--- a/src/controllers/nostr/relay.ts
+++ b/src/controllers/nostr/relay.ts
@@ -10,6 +10,7 @@ import {
 } from '@nostrify/nostrify';
 import { relayInfoController } from '@/controllers/nostr/relay-info.ts';
 import * as pipeline from '@/pipeline.ts';
+import { RelayError } from '@/RelayError.ts';
 import { Storages } from '@/storages.ts';
 
 import type { AppController } from '@/app.ts';
@@ -95,7 +96,7 @@ function connectStream(socket: WebSocket) {
       await pipeline.handleEvent(event, AbortSignal.timeout(1000));
       send(['OK', event.id, true, '']);
     } catch (e) {
-      if (e instanceof pipeline.RelayError) {
+      if (e instanceof RelayError) {
         send(['OK', event.id, false, e.message]);
       } else {
         send(['OK', event.id, false, 'error: something went wrong']);
diff --git a/src/pipeline.ts b/src/pipeline.ts
index a47a2da..995abf2 100644
--- a/src/pipeline.ts
+++ b/src/pipeline.ts
@@ -10,6 +10,7 @@ import { deleteAttachedMedia } from '@/db/unattached-media.ts';
 import { DittoEvent } from '@/interfaces/DittoEvent.ts';
 import { isEphemeralKind } from '@/kinds.ts';
 import { DVM } from '@/pipeline/DVM.ts';
+import { RelayError } from '@/RelayError.ts';
 import { updateStats } from '@/stats.ts';
 import { hydrateEvents, purifyEvent } from '@/storages/hydrate.ts';
 import { Storages } from '@/storages.ts';
@@ -71,15 +72,7 @@ async function policyFilter(event: NostrEvent): Promise<void> {
   const result = await policy.call(event);
   debug(JSON.stringify(result));
 
-  const [_, _eventId, ok, reason] = result;
-  if (!ok) {
-    const [prefix, ...rest] = reason.split(': ');
-    if (['duplicate', 'pow', 'blocked', 'rate-limited', 'invalid'].includes(prefix)) {
-      throw new RelayError(prefix as RelayErrorPrefix, rest.join(': '));
-    } else {
-      throw new RelayError('error', rest.join(': '));
-    }
-  }
+  RelayError.assert(result);
 }
 
 /** Encounter the event, and return whether it has already been encountered. */
@@ -286,13 +279,4 @@ async function streamOut(event: NostrEvent): Promise<void> {
   }
 }
 
-type RelayErrorPrefix = 'duplicate' | 'pow' | 'blocked' | 'rate-limited' | 'invalid' | 'error';
-
-/** NIP-20 command line result. */
-class RelayError extends Error {
-  constructor(prefix: RelayErrorPrefix, message: string) {
-    super(`${prefix}: ${message}`);
-  }
-}
-
-export { handleEvent, RelayError };
+export { handleEvent };
diff --git a/src/utils/api.ts b/src/utils/api.ts
index 8da87fb..70fd995 100644
--- a/src/utils/api.ts
+++ b/src/utils/api.ts
@@ -9,6 +9,7 @@ import { z } from 'zod';
 import { type AppContext } from '@/app.ts';
 import { Conf } from '@/config.ts';
 import * as pipeline from '@/pipeline.ts';
+import { RelayError } from '@/RelayError.ts';
 import { AdminSigner } from '@/signers/AdminSigner.ts';
 import { APISigner } from '@/signers/APISigner.ts';
 import { Storages } from '@/storages.ts';
@@ -106,7 +107,7 @@ async function publishEvent(event: NostrEvent, c: AppContext): Promise<NostrEven
     await pipeline.handleEvent(event, c.req.raw.signal);
     await Storages.client.event(event);
   } catch (e) {
-    if (e instanceof pipeline.RelayError) {
+    if (e instanceof RelayError) {
       throw new HTTPException(422, {
         res: c.json({ error: e.message }, 422),
       });