Environment variables

Variable	Required	Description
CALIBRE_WEB_URL	yes	Root URL of the Calibre-Web instance, e.g. https://books.example.com. The /opds path is appended automatically. Subpath installations (https://host.example/calibre) work.
CALIBRE_WEB_USERNAME	yes¹	Username of the Calibre-Web account. The OPDS feed authenticates with the normal web login via HTTP Basic auth.
CALIBRE_WEB_PASSWORD	yes¹	Password of that account (the web login password — Calibre-Web has no separate API tokens).
CALIBRE_WEB_INSECURE_TLS	no	true to accept self-signed certificates. Scoped to the configured host; never disables TLS validation process-wide.

¹ The credentials count as a pair: leave both unset for an instance that allows anonymous browsing; setting only one of them is a configuration error.

Behaviour without configuration

The server starts and lists its tools even with nothing set — registries and sandbox inspectors can introspect it. Every tool call then fails with setup instructions instead of reaching any host.

Validation at startup

• Fatal: an unparseable URL, a non-http(s) scheme, or credentials embedded in the URL (https://user:pass@host — they would end up in logs; use the dedicated variables).
• Warning: plain http:// to a non-loopback host (the password would cross the network unencrypted), or only one of the two credential variables set.
• CALIBRE_WEB_PASSWORD is deleted from process.env immediately after being read.

Narrowing the tool list

Variable	Required	Description
CALIBRE_WEB_ALLOW_TOOLS	no	Tool names, list_* prefixes or essential; only these register
CALIBRE_WEB_DENY_TOOLS	no	Same syntax; subtracted from whatever the allow list left

Both are comma-separated. Each entry is either an exact tool name or a prefix with a single trailing *. Entries are trimmed and matched case-insensitively; empty entries are ignored, and a value that is empty or only whitespace counts as unset — CALIBRE_WEB_ALLOW_TOOLS= in a compose file does not mean "allow nothing". essential is recognised only in the allow list, and selects search_books, list_books, list_shelves, get_shelf_books, get_stats.

An entry that matches no tool aborts startup, naming the entry and listing the valid names, as does a malformed pattern such as *_x or list_*_x. The alternative — ignoring the entry — leaves a tool missing from tools/list with nothing pointing at the cause. If both lists together remove everything, the server refuses to start rather than offering an empty tool list.