RESP Type Reference

String / str in most languages

Simple strings are non-binary-safe strings terminated by CRLF. The + prefix signals a single-line string that cannot contain \r or \n characters. Used for short server replies like +OK, +PONG, and +QUEUED. For binary-safe string data, use bulk strings ($).

Exception / Error / exception class

Simple errors use the - prefix to signal command failures. The first word in upper case is the error code; the remainder is the human-readable message. Common codes: ERR (generic), WRONGTYPE (type mismatch), NOAUTH (authentication required), NOPERM (ACL permission denied).

Integer / int / Long

Integers use the : prefix and represent a signed 64-bit integer value. Used for command results that are naturally numeric: INCR/DECR return values, LLEN/SCARD counts, EXPIRE success/failure (1/0), PUBLISH subscriber count. The special values 0 and 1 are also used as boolean equivalents for commands that return success/failure.

String / bytes / Optional[str]

Bulk strings are binary-safe strings with an explicit length prefix. Format: $<length>\r\n<bytes>\r\n. The length prefix allows the string to contain any bytes including \r and \n. $-1\r\n represents a null bulk string. Used for most string data returned by Redis: GET values, HGET field values, LRANGE elements.

List / Array / []

Arrays contain an ordered sequence of other RESP types. Format: *<count>\r\n followed by count elements. Arrays can be nested. *-1\r\n is a null array. Used for multi-value replies: LRANGE list elements, KEYS, HMGET values. In RESP3, SMEMBERS returns a ~ set and HGETALL returns a % map instead of flat arrays.

nil / None / null / nullptr

RESP3 introduces a unified null type: _\r\n. This replaces RESP2's two null representations ($-1\r\n null bulk string and *-1\r\n null array), which were semantically identical but required clients to track which null form applied to which command.

float / double / Float64

RESP3 doubles carry IEEE 754 floating-point values natively. Format: ,<number>\r\n. Supports ,inf\r\n and ,-inf\r\n for infinity. Previously, Redis returned floats as bulk strings (e.g., ZSCORE returned '$4\r\n1.25\r\n'), requiring clients to parse the string. RESP3 doubles let clients receive native float/double values directly.

bool / Boolean / true/false

RESP3 booleans encode true and false explicitly: #t\r\n and #f\r\n. In RESP2, boolean-semantic commands returned integers (1=true, 0=false). RESP3 booleans let clients receive proper boolean types for commands like SISMEMBER, HEXISTS, and EXPIRE without knowing the command's boolean-integer convention.

dict / HashMap / Map<K,V> / object

RESP3 maps encode key-value dictionaries natively. Format: %<count>\r\n followed by count×2 elements (alternating keys and values). HGETALL, CONFIG GET, and XAUTOCLAIM now return maps instead of flat alternating arrays. Clients can return native dict/HashMap/object without knowing the command name.

set / Set / HashSet / frozenset

RESP3 sets encode unordered collections with test-for-existence semantics. Format: ~<count>\r\n followed by count elements. SMEMBERS, SUNION, SDIFF, and SINTER now return sets instead of arrays in RESP3. Clients return native set types (Python set, Ruby Set, Java HashSet) without needing to know the command name.

callback / event / async handler

Push data is the most architecturally significant RESP3 addition. A > frame is sent by the server at any time, interleaved with regular replies, without being a response to a command. The first element identifies the push type (pubsub, monitor, keyspace, etc.). Clients invoke registered callbacks. RESP3 push allows pub/sub subscriptions on the same connection used for regular commands.