Nix Cache Info Format
The nix-cache-info file is a metadata file at the root of a binary cache (e.g., https://cache.example.com/nix-cache-info).
MIME type: text/x-nix-cache-info
Format
Line-based key-value format:
Key: value
Leading and trailing whitespace is trimmed from values. Lines without a colon are ignored. Unknown keys are silently ignored.
Fields
StoreDir
The Nix store directory path that this cache was built for (e.g., /nix/store).
If present, Nix verifies that this matches the client's store directory:
error: binary cache 'https://example.com' is for Nix stores with prefix '/nix/store', not '/home/user/nix/store'
WantMassQuery
1 or 0. Sets the default for want-mass-query.
Priority
Integer. Sets the default for priority.
BloomFilter
URL of a Bloom filter that enumerates the store paths held by this cache.
Clients may use it to skip .narinfo requests for paths the filter rules out.
The value is either an absolute URL or a path relative to the cache root:
BloomFilter: /bloom-filter
BloomFilter: https://filters.example.com/cache-abc.bloom
If absent, the cache does not publish a Bloom filter and clients must not assume one is available at any default location.
Example
StoreDir: /nix/store
WantMassQuery: 1
Priority: 30
BloomFilter: /bloom-filter
Caching Behavior
Nix caches nix-cache-info in the cache directory with a 7-day TTL.