diff --git a/R/KorAPConnection.R b/R/KorAPConnection.R
index f7b6af8..967feaa 100644
--- a/R/KorAPConnection.R
+++ b/R/KorAPConnection.R
@@ -5,6 +5,28 @@
 setClassUnion("listOrNULL", c("list", "NULL"))
 # setOldClass("httr2_oauth_client")
 
+#' @rdname KorAPConnection
+#' @export
+setClass("KorAPConnection", slots = c(KorAPUrl = "character", apiVersion = "character", indexRevision = "characterOrNULL", apiUrl = "character", accessToken = "characterOrNULL", oauthClient = "ANY", oauthScope = "characterOrNULL", authorizationSupported = "logical", userAgent = "character", timeout = "numeric", verbose = "logical", cache = "logical", welcome = "listOrNULL"))
+
+generic_kor_app_id <- "99FbPHH7RrN36hbndF7b6f"
+
+kustvakt_redirect_uri <- "http://localhost:1410/"
+kustvakt_auth_path <- "settings/oauth/authorize"
+
+#' Default KorAP server URL
+#'
+#' Returns the KorAP instance URL to connect to if none is given explicitly:
+#' the environment variable `KORAP_URL` if it is set and non-empty, and the
+#' IDS Mannheim KorAP main instance otherwise.
+#'
+#' @return URL of the KorAP instance to connect to by default
+#' @keywords internal
+defaultKorAPUrl <- function() {
+  url <- Sys.getenv("KORAP_URL", unset = "")
+  if (nzchar(url)) url else "https://korap.ids-mannheim.de/"
+}
+
 #' Connect to KorAP Server
 #'
 #' `KorAPConnection()` creates a connection to a KorAP server for corpus queries.
@@ -101,27 +123,32 @@
 #' @import utils
 #' @import methods
 #' @include logging.R
-
 #' @export
-KorAPConnection <- setClass("KorAPConnection", slots = c(KorAPUrl = "character", apiVersion = "character", indexRevision = "characterOrNULL", apiUrl = "character", accessToken = "characterOrNULL", oauthClient = "ANY", oauthScope = "characterOrNULL", authorizationSupported = "logical", userAgent = "character", timeout = "numeric", verbose = "logical", cache = "logical", welcome = "listOrNULL"))
-
-generic_kor_app_id <- "99FbPHH7RrN36hbndF7b6f"
-
-kustvakt_redirect_uri <- "http://localhost:1410/"
-kustvakt_auth_path <- "settings/oauth/authorize"
-
+KorAPConnection <- function(KorAPUrl = defaultKorAPUrl(),
+                            apiVersion = "v1.0",
+                            apiUrl,
+                            accessToken = getAccessToken(KorAPUrl),
+                            oauthClient = NULL,
+                            oauthScope = "search match_info",
+                            authorizationSupported = TRUE,
+                            userAgent = "R-KorAP-Client",
+                            timeout = 240,
+                            verbose = FALSE,
+                            cache = TRUE) {
+  # Forward only the arguments that were actually supplied, so that the
+  # defaults and the `missing()` based overrides of the initialize method
+  # (see below) keep working. The defaults above merely mirror those of the
+  # initialize method to document them (see test-korapconnection-signature.R).
+  args <- as.list(match.call())[-1L]
+  do.call(methods::new, c("KorAPConnection", args), envir = parent.frame())
+}
 
 #' Initialize KorAPConnection object
 #' @keywords internal
 #' @export
 #'
 setMethod("initialize", "KorAPConnection", function(.Object,
-                                                    KorAPUrl = if (is.null(Sys.getenv("KORAP_URL")) |
-                                                      Sys.getenv("KORAP_URL") == "") {
-                                                      "https://korap.ids-mannheim.de/"
-                                                    } else {
-                                                      Sys.getenv("KORAP_URL")
-                                                    },
+                                                    KorAPUrl = defaultKorAPUrl(),
                                                     apiVersion = "v1.0",
                                                     apiUrl,
                                                     accessToken = getAccessToken(KorAPUrl),
diff --git a/man/KorAPConnection-class.Rd b/man/KorAPConnection.Rd
similarity index 93%
rename from man/KorAPConnection-class.Rd
rename to man/KorAPConnection.Rd
index fd306a4..018573f 100644
--- a/man/KorAPConnection-class.Rd
+++ b/man/KorAPConnection.Rd
@@ -5,6 +5,21 @@
 \alias{KorAPConnection-class}
 \alias{KorAPConnection}
 \title{Connect to KorAP Server}
+\usage{
+KorAPConnection(
+  KorAPUrl = defaultKorAPUrl(),
+  apiVersion = "v1.0",
+  apiUrl,
+  accessToken = getAccessToken(KorAPUrl),
+  oauthClient = NULL,
+  oauthScope = "search match_info",
+  authorizationSupported = TRUE,
+  userAgent = "R-KorAP-Client",
+  timeout = 240,
+  verbose = FALSE,
+  cache = TRUE
+)
+}
 \arguments{
 \item{KorAPUrl}{URL of the web user interface of the KorAP server instance you want to access.
 Defaults to the environment variable \code{KORAP_URL} if set and to the IDS Mannheim KorAP main instance
diff --git a/man/defaultKorAPUrl.Rd b/man/defaultKorAPUrl.Rd
new file mode 100644
index 0000000..5da4915
--- /dev/null
+++ b/man/defaultKorAPUrl.Rd
@@ -0,0 +1,17 @@
+% Generated by roxygen2: do not edit by hand
+% Please edit documentation in R/KorAPConnection.R
+\name{defaultKorAPUrl}
+\alias{defaultKorAPUrl}
+\title{Default KorAP server URL}
+\usage{
+defaultKorAPUrl()
+}
+\value{
+URL of the KorAP instance to connect to by default
+}
+\description{
+Returns the KorAP instance URL to connect to if none is given explicitly:
+the environment variable \code{KORAP_URL} if it is set and non-empty, and the
+IDS Mannheim KorAP main instance otherwise.
+}
+\keyword{internal}
diff --git a/man/initialize-KorAPConnection-method.Rd b/man/initialize-KorAPConnection-method.Rd
index 35a92a0..8399c3f 100644
--- a/man/initialize-KorAPConnection-method.Rd
+++ b/man/initialize-KorAPConnection-method.Rd
@@ -6,12 +6,7 @@
 \usage{
 \S4method{initialize}{KorAPConnection}(
   .Object,
-  KorAPUrl = if (is.null(Sys.getenv("KORAP_URL")) | Sys.getenv("KORAP_URL") == "") {
-    
-    "https://korap.ids-mannheim.de/"
- } else {
-     Sys.getenv("KORAP_URL")
- },
+  KorAPUrl = defaultKorAPUrl(),
   apiVersion = "v1.0",
   apiUrl,
   accessToken = getAccessToken(KorAPUrl),
diff --git a/tests/testthat/test-korapconnection-signature.R b/tests/testthat/test-korapconnection-signature.R
new file mode 100644
index 0000000..e8356fe
--- /dev/null
+++ b/tests/testthat/test-korapconnection-signature.R
@@ -0,0 +1,96 @@
+withOfflineKorAPEnv <- function(code, verboseEnv = NA_character_) {
+  oldUrl <- Sys.getenv("KORAP_URL", unset = NA_character_)
+  oldVerbose <- Sys.getenv("KORAP_VERBOSE", unset = NA_character_)
+  on.exit(
+    {
+      if (is.na(oldUrl)) Sys.unsetenv("KORAP_URL") else Sys.setenv(KORAP_URL = oldUrl)
+      if (is.na(oldVerbose)) {
+        Sys.unsetenv("KORAP_VERBOSE")
+      } else {
+        Sys.setenv(KORAP_VERBOSE = oldVerbose)
+      }
+    },
+    add = TRUE
+  )
+  Sys.setenv(KORAP_URL = "https://example.invalid/")
+  if (is.na(verboseEnv)) Sys.unsetenv("KORAP_VERBOSE") else Sys.setenv(KORAP_VERBOSE = verboseEnv)
+  force(code)
+}
+
+test_that("the documented KorAPConnection() defaults are the ones actually used", {
+  # KorAPConnection() only forwards the arguments that were supplied, so its
+  # own defaults are never evaluated. They mirror those of the initialize
+  # method to document them, and this test makes sure that the two cannot
+  # drift apart silently.
+  withOfflineKorAPEnv({
+    kco <- KorAPConnection(accessToken = NULL)
+    documented <- formals(KorAPConnection)
+
+    # accessToken (keyring), apiUrl (derived) and authorizationSupported
+    # (answered by the server) are covered by the tests below instead
+    for (parameter in c(
+      "KorAPUrl", "apiVersion", "oauthClient", "oauthScope",
+      "userAgent", "timeout", "verbose", "cache"
+    )) {
+      expect_equal(
+        slot(kco, parameter),
+        eval(documented[[parameter]]),
+        info = parameter
+      )
+    }
+  })
+})
+
+test_that("KorAPConnection() forwards only the arguments that were supplied", {
+  # `missing()` based overrides in the initialize method must keep working
+  withOfflineKorAPEnv(
+    {
+      expect_true(KorAPConnection(accessToken = NULL)@verbose)
+      # an explicitly passed verbose argument still wins over the env var
+      expect_false(KorAPConnection(accessToken = NULL, verbose = FALSE)@verbose)
+    },
+    verboseEnv = "true"
+  )
+})
+
+test_that("KorAPConnection() derives apiUrl unless it is given explicitly", {
+  kco <- KorAPConnection(KorAPUrl = "https://example.invalid/", accessToken = NULL)
+  expect_equal(kco@apiUrl, "https://example.invalid/api/v1.0/")
+
+  kco <- KorAPConnection(
+    KorAPUrl = "https://example.invalid/",
+    apiUrl = "https://other.invalid/api/",
+    accessToken = NULL
+  )
+  expect_equal(kco@apiUrl, "https://other.invalid/api/")
+})
+
+test_that("KorAPConnection objects can still be created with new()", {
+  kco <- methods::new(
+    "KorAPConnection",
+    KorAPUrl = "https://example.invalid/",
+    apiUrl = "https://example.invalid/api/v1.0/",
+    accessToken = NULL,
+    verbose = FALSE
+  )
+  expect_s4_class(kco, "KorAPConnection")
+  expect_equal(kco@apiUrl, "https://example.invalid/api/v1.0/")
+})
+
+test_that("defaultKorAPUrl() honours KORAP_URL", {
+  old <- Sys.getenv("KORAP_URL", unset = NA_character_)
+  on.exit(
+    if (is.na(old)) Sys.unsetenv("KORAP_URL") else Sys.setenv(KORAP_URL = old),
+    add = TRUE
+  )
+
+  Sys.setenv(KORAP_URL = "https://example.invalid/")
+  expect_equal(defaultKorAPUrl(), "https://example.invalid/")
+
+  # an empty KORAP_URL counts as unset
+  Sys.setenv(KORAP_URL = "")
+  expect_equal(defaultKorAPUrl(), "https://korap.ids-mannheim.de/")
+
+  Sys.unsetenv("KORAP_URL")
+  expect_equal(defaultKorAPUrl(), "https://korap.ids-mannheim.de/")
+})