diff --git a/deps.ts b/deps.ts
index 752a04b..b4f0029 100644
--- a/deps.ts
+++ b/deps.ts
@@ -2,3 +2,4 @@ export * as http from "https://deno.land/std@0.154.0/http/mod.ts";
 export * as log from "https://deno.land/std@0.154.0/log/mod.ts";
 export * as hex from "https://deno.land/std@0.154.0/encoding/hex.ts";
 export * as redis from "https://deno.land/x/redis@v0.27.0/mod.ts";
+export { default as TTLCache } from "https://deno.land/x/ttl@1.0.1/mod.ts";
diff --git a/lib/config.ts b/lib/config.ts
index 445f508..cf96e8a 100644
--- a/lib/config.ts
+++ b/lib/config.ts
@@ -17,7 +17,7 @@ export default {
     maxWebhookRetries: parseInt(get("MAX_RETRIES", "3")),
     maxWebhookRetryMs: parseInt(get("MAX_RETRY_MS", "30000")),
     mainRedirect: get("MAIN_REDIRECT", null),
-    redisUrl: get("REDIS_URL"),
+    redisUrl: get("REDIS_URL", null),
 
     // set by deno deploy
     deployId: get("DENO_DEPLOYMENT_ID", "<unknown>"),
diff --git a/lib/filter.ts b/lib/filter.ts
index 753b25c..9d3da99 100644
--- a/lib/filter.ts
+++ b/lib/filter.ts
@@ -1,4 +1,4 @@
-import { reviewCommentManager } from "./manager.ts";
+import { commentManager } from "./manager.ts";
 import { UrlConfig } from "./types.d.ts";
 import { requestLog } from "./util.ts";
 
@@ -36,21 +36,25 @@ export default async function filter(
     if (event === "pull_request_review") {
         // ignore edit/dismiss actions
         if (json.action !== "submitted") return `no-op PR review action '${json.action}'`;
+
         // if comment (not approval or changes requested), ignore empty review body
-        else if (json.review?.state === "commented" && !json.review?.body) return "empty PR review";
+        if (json.review?.state === "commented" && !json.review?.body) return "empty PR review";
     }
 
     // ignore some PR comment events
     if (event === "pull_request_review_comment") {
         // ignore edit/delete actions
         if (json.action !== "created") return `no-op PR comment action '${json.action}'`;
+
         // check if more than x comments on a PR review in a short timespan
         const reviewId: number = json.comment?.pull_request_review_id;
         if (config.commentBurstLimit && reviewId) {
             const cacheKey = `${reviewId}-${login}`;
+
             reqLog.debug(`filter: checking cache key ${cacheKey}`);
-            const curr = await reviewCommentManager.getAndIncrement(cacheKey);
+            const curr = await commentManager.getAndIncrement(cacheKey);
             reqLog.debug(`filter: current value: ${curr}`);
+
             if (curr && curr >= config.commentBurstLimit) {
                 return `exceeded comment burst limit (${config.commentBurstLimit}) for review ${reviewId}`;
             }
diff --git a/lib/manager.ts b/lib/manager.ts
index 78fce32..1177284 100644
--- a/lib/manager.ts
+++ b/lib/manager.ts
@@ -1,23 +1,45 @@
-import { redis } from "../deps.ts";
+import { redis, TTLCache } from "../deps.ts";
 import config from "./config.ts";
 
-class ReviewCommentManager {
-    private redis: redis.Redis;
+const KEY_EXPIRY = 3; // seconds
+
+interface CommentManager {
+    getAndIncrement(key: string): Promise<number>;
+}
+
+class LocalCommentManager implements CommentManager {
+    private cache: TTLCache<number>;
     constructor() {
+        this.cache = new TTLCache(KEY_EXPIRY * 1000);
+    }
+
+    getAndIncrement(key: string): Promise<number> {
+        const value = this.cache.get(key) ?? 0;
+        this.cache.set(key, value + 1);
+        return Promise.resolve(value);
+    }
+}
+
+class RedisCommentManager implements CommentManager {
+    private redis: redis.Redis;
+    constructor(redisUrl: string) {
         this.redis = redis.createLazyClient({
-            ...redis.parseURL(config.redisUrl),
+            ...redis.parseURL(redisUrl),
             maxRetryCount: 3,
         });
     }
 
     async getAndIncrement(key: string): Promise<number> {
+        key = `reviewcomment:${key}`;
+
+        // seems like pipelines don't quite work with the lazy client, so force a connection
         if (!this.redis.isConnected) {
-            // seems like pipelines don't quite work with the lazy client
             await this.redis.ping();
         }
+
         const pl = this.redis.pipeline();
-        pl.incr(`reviewcomment:${key}`);
-        pl.expire(`reviewcomment:${key}`, 3);
+        pl.incr(key);
+        pl.expire(key, KEY_EXPIRY);
         const results = await pl.flush();
 
         const newValue = results[0] as number;
@@ -25,4 +47,6 @@ class ReviewCommentManager {
     }
 }
 
-export const reviewCommentManager = new ReviewCommentManager();
+export const commentManager = config.redisUrl
+    ? new RedisCommentManager(config.redisUrl)
+    : new LocalCommentManager();