Environment variables

Variable	Required	Default	Description
HEALTHCHECKS_API_KEY	yes	—	Project API key, exactly 32 characters. Read-only or read-write
HEALTHCHECKS_URL	no	https://healthchecks.io	Site root of a self-hosted instance. A trailing /api/vN is trimmed
HEALTHCHECKS_READ_ONLY	no	false	true registers only the read tools
HEALTHCHECKS_ALLOW_TOOLS	no	—	Tool names, list_* prefixes or essential; only these register
HEALTHCHECKS_DENY_TOOLS	no	—	Same syntax; subtracted from whatever the allow list left
HEALTHCHECKS_INSECURE_TLS	no	false	true accepts self-signed certificates, scoped to this connection
ELICITATION	no	true	false replaces the approval dialog with the two-call token. Not prefixed

The HEALTHCHECKS_* booleans are the exact string true; anything else, including 1 and TRUE, is false. ELICITATION is the exception in both directions — see below.

ELICITATION

Whether a client that can show a dialog is asked before delete_check acts. Default true. false takes the two-call-token path instead — it does not remove the guard, and a server started with it off prints one line saying so.

Two ways it differs from every other variable here:

• No prefix. One export ELICITATION=false reaches every MCP server in the same environment, not just this one. That is the point of it and also its risk; see Asking a person.
• Fatal on anything else. 1, off or a typo stop the server with exit code 1 rather than falling back to the default. It is the only variable of this family that defaults to on, and a typo that fell back would leave the dialog running while you believed it was off.

Values are trimmed and matched case-insensitively. It is read afterHEALTHCHECKS_API_KEY is deleted from process.env, so the fatal path cannot leave the key sitting there for a crash reporter.

HEALTHCHECKS_API_KEY

Per project, not per account — Project Settings → API Access. Exactly 32 characters; the upstream answers any other length with 401 missing api key, which looks like a header that never arrived, so the server checks the length itself at startup and before each call.

Read from the environment once and then deleted from process.env, so it is not visible to child processes. It is sent as X-Api-Key and never in a request body.

A read-only key (hcr_… on the hosted service) reaches list_checks, get_check, list_flips and list_badges. It does not reach list_pings, get_ping_body, list_integrations or any write tool. See read-only and read-write keys.

HEALTHCHECKS_URL

The site root of a self-hosted instance: https://hc.example.net. Must be http: or https: and must not carry user:pass@ credentials — both are fatal at startup, because a malformed target is the one misconfiguration that can send the key to the wrong host. Plain http to a non-loopback host warns and continues.

A value ending in /api/v1, /api/v2 or /api/v3 is trimmed back to the site root, so a URL copied out of the API documentation works as well as the short one.

Narrowing the tool list

The syntax, exactly; for why you would want it, see choosing the tools that load.

HEALTHCHECKS_ALLOW_TOOLS and HEALTHCHECKS_DENY_TOOLS are comma-separated. Each entry is either an exact tool name or a prefix with a single trailing *:

Value	Registers
essential	the curated preset, marked in the tool reference
list_*,get_check	exactly those
list_*	every tool whose name starts with list_
*	everything — the same as leaving it unset

Entries are trimmed and matched case-insensitively; empty entries are ignored, and a value that is empty or only whitespace counts as unset — HEALTHCHECKS_ALLOW_TOOLS= in a compose file does not mean "allow nothing". essential is recognised only in the allow list.

An entry that matches no tool aborts startup, naming the entry and listing the valid names, as does a malformed pattern such as *_check 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.

Under HEALTHCHECKS_READ_ONLY, an exact write-tool name in the allow list is an error naming the read-only setting rather than "unknown tool"; a pattern covering write tools is accepted and merely contributes nothing, with a warning on stderr. Deny entries are exempt: denying an already-suppressed tool is how a defensive list is written.