What causes "redis: unexpected type=%T for Bool" in go-redis/redis?

Use the typed command (Exists → BoolCmd; SetNX → BoolCmd; SIsMember → BoolCmd).

redis: unexpected type=%T for Bool

Error message

redis: unexpected type=%T for Bool

What it means

Returned by toBool (command.go:764) when Cmd.Bool() is called on a reply value that is neither bool, int64, nor string. bool is returned directly; int64 is true if non-zero; string is parsed via strconv.ParseBool; any other type (array, nil, map) yields this error. Means the command did not return a single boolean-like scalar.

Source

Thrown at command.go:773

func (cmd *Cmd) Bool() (bool, error) {
	cmd.await()
	if cmd.err != nil {
		return false, cmd.err
	}
	return toBool(cmd.val)
}

func toBool(val interface{}) (bool, error) {
	switch val := val.(type) {
	case bool:
		return val, nil
	case int64:
		return val != 0, nil
	case string:
		return strconv.ParseBool(val)
	default:
		err := fmt.Errorf("redis: unexpected type=%T for Bool", val)
		return false, err
	}
}

func (cmd *Cmd) Slice() ([]interface{}, error) {
	cmd.await()
	if cmd.err != nil {
		return nil, cmd.err
	}
	switch val := cmd.val.(type) {
	case []interface{}:
		return val, nil
	default:
		return nil, fmt.Errorf("redis: unexpected type=%T for Slice", val)
	}
}

func (cmd *Cmd) StringSlice() ([]string, error) {

View on GitHub (pinned to 36d97525cd)

Solutions

Use the typed command (Exists → BoolCmd; SetNX → BoolCmd; SIsMember → BoolCmd).
Type-switch on cmd.Result() when using Do.
Check cmd.Err() for redis.Nil before reading the value.

Example fix

// before
ok, err := client.Do(ctx, "EXISTS", "k").Bool()

// after
ok, err := client.Exists(ctx, "k").Result()

Defensive patterns

Strategy: type-guard

Type guard

func asBool(cmd *redis.Cmd) (bool, error) {
    if err := cmd.Err(); err != nil { return false, err }
    switch v := cmd.Val().(type) {
    case bool:
        return v, nil
    case int64:
        return v != 0, nil
    case string:
        return strconv.ParseBool(v)
    default:
        return false, fmt.Errorf("not a bool: %T", v)
    }
}

Try / catch

ok, err := cmd.Bool()
if err != nil && strings.Contains(err.Error(), "unexpected type") {
    // reply was not boolean-like — use Exists/SIsMember/SetNX
}

Prevention

Use BoolCmd-returning methods (Exists, SetNX, SIsMember) for boolean replies.
Distinguish redis.Nil from a present false value before coercing.
Type-switch on Result() for raw Do replies.

When it happens

Trigger: Calling Bool() on a raw Cmd holding an array reply; calling Bool() on a nil value when redis.Nil was not surfaced as cmd.err; using Bool() where Exists/BoolSliceCmd is the correct accessor.

Common situations: Generic Do Cmd used for a command returning arrays; expecting a bool from a command whose value came back as []interface{}; confusing cmd.Err()==redis.Nil with a present-but-false value.

Related errors

AI-assisted analysis of go-redis/redis@36d97525cd (2026-08-06). Data as JSON: /data/errors/ee1d9cd0d0e3a6b5.json. Report an issue: GitHub.