api-database-vercel-kv

Vercel KV / Upstash Redis Patterns

Quick Guide: Use @upstash/redis (the successor to @vercel/kv) for serverless, edge-compatible Redis via REST API. Key gotchas: REST adds ~5-15ms latency per call vs TCP Redis, all values are auto-serialized as JSON (objects round-trip transparently but Date objects become strings), pipeline/multi execute as single HTTP requests but pipeline is NOT atomic. Use Redis.fromEnv() for automatic connection. Always set TTLs -- serverless Redis is billed per command.

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<critical_requirements>

CRITICAL: Before Using This Skill

All code must follow project conventions in CLAUDE.md (kebab-case, named exports, import ordering, import type, named constants)

(You MUST use @upstash/redis for new projects -- @vercel/kv was deprecated in December 2024 and all stores were migrated to Upstash Redis)

(You MUST set TTLs on all cached data -- serverless Redis is billed per command and has storage limits per plan)

(You MUST understand that this is a REST/HTTP client, NOT a TCP Redis client -- each command is an HTTP request with ~5-15ms overhead, so batch with pipelines when possible)

</critical_requirements>

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Examples

• Core Patterns -- Client setup, CRUD operations, TTL, hashes, pipelines, transactions, rate limiting, sessions

Additional resources:

• reference.md -- Command quick reference, environment variables, plan limits

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Auto-detection: Vercel KV, @vercel/kv, @upstash/redis, Upstash Redis, KV_REST_API_URL, KV_REST_API_TOKEN, UPSTASH_REDIS_REST_URL, UPSTASH_REDIS_REST_TOKEN, Redis.fromEnv, kv.set, kv.get, kv.hset, kv.hget, kv.incr, kv.expire, kv.del, createClient, automaticDeserialization, edge Redis, serverless Redis

When to use:

• Caching API responses or database queries in Vercel serverless/edge functions
• Rate limiting at the edge (sliding window counters)
• Session storage for serverless applications
• Feature flags, A/B test assignments, or short-lived counters
• Any Redis use case on Vercel where TCP connections are unavailable (edge runtime)

Key patterns covered:

• Client initialization (Redis.fromEnv(), new Redis())
• Basic CRUD with automatic JSON serialization
• TTL and expiration strategies
• Hash operations for structured data
• Pipelines (batched HTTP) and transactions (atomic MULTI/EXEC)
• Rate limiting with sorted sets
• Session storage patterns

When NOT to use:

• High-throughput, low-latency Redis workloads (use ioredis with TCP -- REST adds per-request overhead)
• Pub/Sub subscribers (REST is request-response, not persistent connections)
• Redis Streams consumers (requires TCP client like ioredis)
• Large value storage (>1 MB per record on free tier, billed by command count)
• Primary database (Redis is a cache/ephemeral store, not a source of truth)

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Philosophy

Upstash Redis (formerly Vercel KV) is a serverless, REST-based Redis designed for edge and serverless runtimes where TCP connections are unavailable or impractical. The core trade-off: HTTP compatibility everywhere, at the cost of per-request latency overhead.

Core principles:

1. REST-first -- Every Redis command is an HTTP request. This works everywhere (edge, serverless, browsers) but adds ~5-15ms per call. Batch with pipelines.
2. Auto-serialization -- Objects are JSON-serialized on write and deserialized on read. This is convenient but means Date objects, Map, Set, and functions are not preserved faithfully.
3. Ephemeral by design -- Set TTLs on everything. Serverless Redis is billed per command and has storage caps. Treat it as a cache, not a database.
4. Zero connection management -- No connection pools, no reconnection logic, no error event handlers. Each request is stateless HTTP.

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Core Patterns

Full implementations with good/bad pairs: examples/core.md

Pattern 1: Client Initialization

Two approaches: Redis.fromEnv() (preferred on Vercel -- reads UPSTASH_REDIS_REST_URL and UPSTASH_REDIS_REST_TOKEN automatically) or new Redis({ url, token }) for explicit configuration. Never hardcode credentials.

import { Redis } from "@upstash/redis";
const redis = Redis.fromEnv();
export { redis };

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Pattern 2: Automatic JSON Serialization

The SDK auto-serializes objects to JSON on write and deserializes on read. Never call JSON.stringify manually -- it causes double-serialization. Use get<T>() for typed returns, satisfies for type-safe writes. Date objects become ISO strings on round-trip -- store timestamps as numbers instead.

await redis.set("user:123", data satisfies UserProfile, { ex: TTL_SECONDS });
const user = await redis.get<UserProfile>("user:123"); // UserProfile | null

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Pattern 3: TTL and Expiration

Always set TTLs -- serverless Redis is billed per command. Use { ex: seconds } or { px: milliseconds } on set(). Use { nx: true } for distributed locks (returns "OK" or null). Keys without TTLs cause unbounded storage growth.

await redis.set("cache:key", data, { ex: CACHE_TTL_SECONDS });

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Pattern 4: Hash Operations

Hashes enable partial field reads/writes without serializing entire objects. Use hset for multi-field writes, hget/hgetall for reads, hincrby for atomic counters. Note: hset does not accept TTL directly -- call expire() separately. hgetall returns null for missing keys (not {}).

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Pattern 5: Pipelines and Transactions

Pipelines (redis.pipeline()) batch commands into a single HTTP request but are NOT atomic. Transactions (redis.multi()) provide atomic MULTI/EXEC, also as a single HTTP request. Avoid sequential calls when multiple commands can be batched -- each call is a separate HTTP round-trip.

const pipe = redis.pipeline();
pipe.set("k1", "v1", { ex: TTL });
pipe.incr("counter");
const results = await pipe.exec<[string, number]>();

Important: Upstash REST transactions do NOT support WATCH for optimistic locking.

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Pattern 6: Rate Limiting (Sliding Window)

Sliding window via sorted set scores -- zadd with timestamp as score, zremrangebyscore to prune expired entries, zcard to count, all batched in a pipeline. For production rate limiting, consider @upstash/ratelimit which provides built-in algorithms.

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Pattern 7: Cache-Aside Helper

Generic cacheAside<T>(key, fetcher, ttl) pattern: check cache first, fetch on miss, fire-and-forget cache write to avoid blocking responses on cache failures.

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<decision_framework>

Decision Framework

Upstash Redis vs ioredis/node-redis?

Which Redis client should I use?
+-- Running in Vercel Edge Runtime? -> @upstash/redis (only option -- no TCP)
+-- Running in Vercel Serverless Functions? -> @upstash/redis (simpler) or ioredis (if you need TCP features)
+-- Need Pub/Sub subscribers? -> ioredis (REST cannot maintain subscriptions)
+-- Need Redis Streams consumers? -> ioredis (requires persistent TCP connection)
+-- Need lowest possible latency (<1ms)? -> ioredis with TCP (REST adds HTTP overhead)
+-- Simple caching/sessions/counters? -> @upstash/redis (zero connection management)

Pipeline vs Transaction vs Sequential?

How should I batch commands?
+-- Need atomicity (all-or-nothing)? -> redis.multi() (transaction)
+-- Just reducing HTTP round-trips? -> redis.pipeline() (non-atomic batch)
+-- Single independent command? -> Direct call (redis.set, redis.get, etc.)

</decision_framework>

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<red_flags>

RED FLAGS

High Priority Issues:

• Using @vercel/kv in new projects -- deprecated December 2024, use @upstash/redis instead
• Missing TTLs on cached keys -- causes unbounded storage growth and unexpected billing
• Manual JSON.stringify/JSON.parse with Upstash Redis -- causes double-serialization because the SDK auto-serializes all values
• Assuming pipeline commands are atomic -- pipelines batch for HTTP efficiency but do NOT guarantee atomicity (use multi() for atomic execution)

Medium Priority Issues:

• Making sequential Redis calls where a pipeline would work -- each call is a separate HTTP round-trip (~5-15ms each)
• Storing values >1 MB -- REST requests have size limits per plan (100 MB max on free/pay-as-you-go, but large values degrade performance)
• Using Upstash Redis as a primary database -- it's a cache/ephemeral store, always have a source of truth elsewhere

Common Mistakes:

• Expecting hgetall to return an empty object {} for missing keys -- Upstash returns null (unlike ioredis which returns {})
• Forgetting that get() returns null (not undefined) for missing keys
• Passing Date objects and expecting them to survive round-trip -- they serialize to ISO strings and come back as strings, not Date instances

Gotchas & Edge Cases:

• automaticDeserialization: false breaks many TypeScript types -- only disable if you need raw string responses and are prepared to handle typing manually
• set with ex option resets TTL on overwrite (standard Redis behavior) -- if you set a key that already has a TTL, the new ex value replaces it
• REST latency is per-request, not per-command -- a pipeline with 10 commands has the same HTTP overhead as a single command (one round-trip)
• Free tier is limited to 500K commands/month and 256 MB storage -- monitor usage in production
• nx (set-if-not-exists) returns null on failure, "OK" on success -- check the return value explicitly

</red_flags>

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<critical_reminders>

CRITICAL REMINDERS

All code must follow project conventions in CLAUDE.md (kebab-case, named exports, import ordering, import type, named constants)

(You MUST use @upstash/redis for new projects -- @vercel/kv was deprecated in December 2024 and all stores were migrated to Upstash Redis)

(You MUST set TTLs on all cached data -- serverless Redis is billed per command and has storage limits per plan)

(You MUST understand that this is a REST/HTTP client, NOT a TCP Redis client -- each command is an HTTP request with ~5-15ms overhead, so batch with pipelines when possible)

Failure to follow these rules will cause deprecated package usage, unbounded storage costs, and unnecessary latency in serverless functions.

</critical_reminders>