The config file
Paste a redis.conf or valkey.conf, or drop the file here. The checker reads it line by line the way the server you pick reads it at startup, and tells you whether that server would start.
The file never leaves your browser.
What the server does
A running server
Paste the output of CONFIG GET * from redis-cli or valkey-cli to see which settings differ from the defaults of its version. Add --raw for the shortest output; the numbered kind works too.
redis-cli --raw CONFIG GET '*' > config.txt