How to fix ERR syntax error in Redis

Test the failing command directly in redis-cli to isolate the issue:

redis-cli
127.0.0.1:6379> SET mykey "hello world"
OK
127.0.0.1:6379> GET mykey
"hello world"

If the command works in redis-cli but fails in your application, the issue is with how your client library sends the command, not with Redis itself.

Verify you're sending the correct number of arguments. Check the Redis command documentation:

# WRONG: SET requires exactly 2 args (key, value)
SET mykey

# CORRECT
SET mykey "myvalue"

# WRONG: GET requires exactly 1 arg
GET key1 key2

# CORRECT
GET key1

Use COMMAND INFO command-name in redis-cli to see exact argument requirements.

In RESP protocol, arguments with spaces must be properly formatted as bulk strings:

# Wrong (spaces without encoding)
SET mykey hello world

# Correct RESP2 format
*3\r\n$3\r\nSET\r\n$5\r\nmykey\r\n$11\r\nhello world\r\n

# Using redis-cli with proper quoting
SET mykey "hello world"

Most client libraries handle this automatically, but if using raw socket connections, ensure proper bulk string encoding.

Outdated client libraries may have RESP protocol bugs. Update to the latest stable version:

# Node.js
npm update redis

# Python
pip install --upgrade redis

# Ruby
gem update redis

# Java
# Update Jedis or Lettuce in pom.xml/build.gradle

Check the client library changelog for syntax error fixes and protocol improvements.

If using Redis 6.0+, ensure your client supports the same RESP version:

# Check Redis RESP version support
redis-cli HELLO 3

# In your client, explicitly set RESP version if needed
# Node.js example:
const redis = require('redis');
const client = redis.createClient({
  socket: { host: 'localhost', port: 6379 },
  protocol: 'resp2', // or 'resp3'
});

Most clients default to RESP2 for compatibility with older Redis versions.

Use Redis MONITOR to see exactly what your client is sending:

# Terminal 1: Start monitoring
redis-cli MONITOR

# Terminal 2: Run your client code
# Watch Terminal 1 output to see the exact command format sent

This reveals if your client is sending malformed RESP. Look for:
- Missing type markers ($, *, etc.)
- Incorrect length specifications
- Missing CRLF terminators
- Non-printable or unexpected characters

If only some commands fail, the connection may be in a bad state:

# Test basic connectivity
redis-cli PING

# If using connection pools, try disconnecting and reconnecting
# If using Lua scripts, ensure they're not corrupting state

Close and reopen connections. If the issue persists after reconnecting, it's not a connection state problem.

When dealing with binary data or reading from files, ensure proper encoding:

# Node.js: Ensure buffers are properly handled
const key = 'mykey';
const value = Buffer.from('hello\x00world'); // Binary data
await client.set(key, value);

# Python: Use bytes for binary data
import redis
r = redis.Redis(decode_responses=False) # Binary mode
r.set(b'mykey', b'hello\x00world')

If reading from files, avoid extra whitespace or hidden characters. Use xxd or od to inspect raw bytes.