Glossary

ACME — the protocol Caddy uses to obtain and renew certificates from Let's Encrypt automatically: prove control of a domain, receive a certificate.

Admin API — the REST API a running Caddy exposes (default localhost:2019) for inspecting and replacing its live config. caddy reload is a client of it.

Adapt — compiling a Caddyfile into the JSON config Caddy actually runs (caddy adapt).

Basic auth — HTTP's built-in username/password prompt. In Caddy: the basic_auth directive, passwords stored as bcrypt hashes.

Caddyfile — Caddy's human config format: site blocks of directives. Adapts to JSON at load time.

Directive — one instruction inside a site block (root, file_server, reverse_proxy, respond...).

Internal CA — Caddy's built-in certificate authority for names the public internet can't verify (localhost, LAN names), enabled with tls internal. Trust requires installing its root certificate.

Let's Encrypt — the free, automated public certificate authority Caddy uses by default.

Matcher — a pattern narrowing a directive's reach: a path (/health), a named set (@lan), * for all.

Placeholder — a runtime value in a config or log format: {uri}, {host}, {remote}.

Reverse proxy — a server that receives requests and forwards them to an app behind it, relaying responses — Caddy's most common job.

Site block — one address line plus its braced directives: the unit of Caddyfile organization.

Upstream — the app behind a proxy: the dial address in reverse_proxy 127.0.0.1:8080.

Via / X-Forwarded- — headers a proxy adds so the app knows the original visitor: their address (X-Forwarded-For), the name and scheme they used.