Environment variables

Every variable this server reads, in full. There is no configuration file.

Only CARDDAV_URL plus one credential pair is required; everything else has a default that is safe to leave alone.

Connection

Variable	Required	Default	Description
CARDDAV_URL	yes	—	Root of the CardDAV server, e.g. https://dav.example.net. An address book collection URL works too and limits the server to that one book. A query string or a fragment is refused.
CARDDAV_USERNAME	yes¹	—	Account name. Deleted from the process environment once read.
CARDDAV_PASSWORD	yes¹	—	Password, or an app-specific password. Deleted from the process environment once read.
CARDDAV_TOKEN	yes¹	—	Bearer token, instead of username and password. Setting both is refused at startup. Deleted from the process environment once read.

¹ Either CARDDAV_USERNAME and CARDDAV_PASSWORD, or CARDDAV_TOKEN. Not both — which was meant is not knowable from here, and the wrong guess authenticates as somebody else.

Almost every CardDAV server wants the username and password. CARDDAV_TOKEN exists for the rare one that does not.

Scope

Variable	Required	Default	Description
CARDDAV_ADDRESSBOOKS	no	every book the account can see	Comma-separated address books this server may touch, each a full URL, an absolute path, or the collection's final path segment. A display name is not accepted — it is chosen by whoever shared the book, is not unique, and changes.
CARDDAV_MAX_CONTACTS	no	100	Contacts a listing returns when the caller passes no limit. An integer from 1 to 500.
CARDDAV_READ_ONLY	no	false	true registers only the read tools. They do not appear in tools/list at all rather than failing when called.
CARDDAV_ALLOW_TOOLS	no	all tools	Comma-separated tool names, a prefix with one trailing *, or essential for the curated preset. A name matching no tool stops the server at startup.
CARDDAV_DENY_TOOLS	no	—	Same shape, subtracted from whatever the allow list left.

Setting CARDDAV_ADDRESSBOOKS to an empty string is a refusal, not an omission: whoever wrote CARDDAV_ADDRESSBOOKS= in a compose file meant to restrict something, and answering that by opening every book is the one wrong outcome. An entry matching two books stops the server rather than picking one.

Transport security

Variable	Required	Default	Description
CARDDAV_INSECURE_TLS	no	false	true accepts a self-signed certificate on the configured host only, through a scoped dispatcher. NODE_TLS_REJECT_UNAUTHORIZED is never set.
CARDDAV_ALLOW_PLAINTEXT	no	false	true allows a plain http:// URL to a host that is not loopback. Without it such a URL refuses to start, because it would send the credentials and every contact unencrypted on every request.

A loopback URL needs neither. http://127.0.0.1:5232, http://localhost:5232, http://[::1]:5232 and http://[::ffff:127.0.0.1]:5232 are all recognised as local — the classification is numeric rather than a string comparison, so 127.example.com is not.

Asking a person

Variable	Required	Default	Description
ELICITATION	no	true	Not prefixed. false makes guarded tools use the two-call token instead of raising a dialog. Anything else is fatal.

ELICITATION is deliberately unprefixed, which means one export ELICITATION=false reaches every MCP server in the environment. That is its risk as well as its point, so a server started with it off prints a line saying so.

It is also the only variable here that defaults to on, which is why an unrecognised value stops the server instead of being ignored: failing open on a typo would leave the dialog running while the operator believed it was off.

See asking a person.

How booleans are read

The direction decides the strictness, not the variable.

A switch that turns a protection on is read tolerantly — 1, true, TRUE, yes, with surrounding whitespace ignored. That is CARDDAV_READ_ONLY. An === 'true' comparison would answer CARDDAV_READ_ONLY=1 in a compose file with a server that quietly exposes every write tool, and the operator would not find out.

A switch that lifts a protection is compared against the exact string true. That is CARDDAV_INSECURE_TLS and CARDDAV_ALLOW_PLAINTEXT. Anything the operator did not spell exactly leaves the protection in place.

What is not here

For completeness, because a reader may be looking for them:

• No timezone variable. vCard has no timezones. A BDAY is a date, and one without a year stays without a year.
• No user-email variable. vCard has no attendees and no scheduling, so there is nothing this server would need to recognise you by.
• No cache or state directory. This server keeps no local copy of anything. The only state it holds is a five-minute memo of which address books exist, in memory, and list_address_books always refreshes it.