diff --git a/README.md b/README.md
index fe16e17..8969b89 100644
--- a/README.md
+++ b/README.md
@@ -31,11 +31,7 @@ This works on any Gitea or Forgejo instance.
 
 ### Can I migrate specific repositories?
 
-Sure, just pass the URLs to them as arguments:
-
-```nu
-./migrate.nu https://github.com/RGBCube/Foo https://github.com/RGBCube/Bar
-```
+Nope. Just use the Gitea/Forgejo web UI for that.
 
 ## License
 
diff --git a/migrate.nu b/migrate.nu
index 37ad5d0..e0b3ad7 100755
--- a/migrate.nu
+++ b/migrate.nu
@@ -19,89 +19,98 @@ def or-default [default: closure] {
 # GITEA_USER: The user to migrate the repositories to.
 # GITEA_TOKEN: An access token for the user to actually insert repositories to.
 # STRATEGY: The strategy. Valid options are "mirrored" or "cloned" (case insensitive).
-def main [
-  ...repo_urls: string # The GitHub repo URLs to migrate to Gitea or Forgejo. If not given, all will be fetched.
-] {
-  let github_user = $env | get -i GITHUB_USER | or-default { input $"(ansi red)GitHub username: (ansi reset)" }
+# FORCE_SYNC: Whether to delete a mirrored repo from Gitea or Forgejo if the source on GitHub doesn't exist anymore. Must be either "true" or "false".
+def main [] {
+  let github_user  = $env | get -i GITHUB_USER  | or-default { input $"(ansi red)GitHub username: (ansi reset)" }
   let github_token = $env | get -i GITHUB_TOKEN | or-default { input $"(ansi red)GitHub access token (ansi yellow)\((ansi blue)optional, only used for private repositories(ansi yellow))(ansi red): (ansi reset)" }
+  let gitea_url    = $env | get -i GITEA_URL    | or-default { input $"(ansi green)Gitea instance URL \(with https://): (ansi reset)" } | str trim --right --char "/"
+  let gitea_user   = $env | get -i GITEA_USER   | or-default { input $"(ansi green)Gitea username or organization to migrate to: (ansi reset)" }
+  let gitea_token  = $env | get -i GITEA_TOKEN  | or-default { input $"(ansi green)Gitea access token: (ansi reset)" }
+  let strategy     = $env | get -i STRATEGY     | or-default { [ Mirrored Cloned ] | input list $"(ansi cyan)Should the repos be mirrored, or just cloned once?(ansi reset)" } | str downcase
+  let force_sync   = $env | get -i FORCE_SYNC   | or-default { [ "Yup, delete them" Nope ] | input list $"(ansi yellow)Should mirrored repos that don't have a GitHub source anymore be deleted?(ansi reset)" } | $in != "Nope"
 
-  let gitea_url = $env | get -i GITEA_URL | or-default { input $"(ansi green)Gitea instance URL \(with https://): (ansi reset)" } | str trim --right --char "/"
-
-  let gitea_user = $env | get -i GITEA_USER | or-default { input $"(ansi green)Gitea username or organization to migrate to: (ansi reset)" }
-  let gitea_token = $env | get -i GITEA_TOKEN | or-default { input $"(ansi green)Gitea access token: (ansi reset)" }
-
-  let gitea_uid = (
-    http get $"($gitea_url)/api/v1/users/($gitea_user)"
-    -H [ Authorization $"token ($gitea_token)" ]
-  ) | get -i id
-
-  if $gitea_uid == null {
-    echo "Invalid Gitea username or password"
-    exit 1
-  }
-
-  let strategy = $env | get -i STRATEGY | or-default { [ Mirrored Cloned ] | input list $"(ansi cyan)Should the repos be mirrored, or just cloned once? (ansi reset)" } | str downcase
-
-  let repo_urls = if ($repo_urls | length) != 0 {
-    $repo_urls
-  } else {
+  def get-repos [page_nr: number] {
     if $github_token != "" {
-      (
-        http get $"https://api.github.com/users/($github_user)/repos?per_page=100"
-        -H [ Authorization $"token ($github_token)" ]
-      )
-      | get html_url
+      (http get $"https://api.github.com/user/repos?per_page=100&page=($page_nr)"
+      -H [ Authorization $"token ($github_token)" ])
     } else {
-      http get $"https://api.github.com/users/($github_user)/repos?per_page=100"
-      | get html_url
+      http get $"https://api.github.com/users/($github_user)/repos?per_page=100?page=($page_nr)"
+      exit
     }
   }
 
-  $repo_urls | each {|url|
-    let repo_name = $url | split row "/" | last
+  mut github_repos = []
+  mut github_repo_page_nr = 1
 
-    let repo_is_private = if ($github_token | is-empty) {
-      false
+  loop {
+    let next_repos = get-repos $github_repo_page_nr
+    $github_repos = ($github_repos | append $next_repos)
+
+    if ($next_repos | length) >= 100 {
+      $github_repo_page_nr += 1
     } else {
-      (
-        http get ("https://api.github.com/repos/" + $github_user + "/" + $repo_name)
-        -H [ Authorization $"token ($github_token)" ]
-      ).private
+      break
+    }
+  }
+
+  $github_repos = ($github_repos | filter { get owner.login | $in == $github_user })
+
+  # Delete mirrored repos that do not exist on GitHub.
+  if $force_sync {
+    let github_repo_names = ($github_repos | get name)
+
+    let gitea_mirrored_repos = (
+      http get $"($gitea_url)/api/v1/user/repos"
+        -H [ Authorization $"token ($gitea_token)" ]
+      | filter { get mirror }
+    )
+
+    let gitea_not_on_github = ($gitea_mirrored_repos | filter { not ($in.name in $github_repo_names) })
+
+    $gitea_not_on_github | each {|repo|
+      print --no-newline $"(ansi red)Deleting ($gitea_url)/($repo.full_name) because the mirror source doesn't exist on GitHub anymore...(ansi reset)"
+
+      (http delete $"($gitea_url)/api/v1/repos/($repo.full_name)"
+        -H [ Authorization $"token ($gitea_token)" ])
+
+      print $" (ansi green)Success!(ansi reset)"
+    }
+  }
+
+  # Mirror repos that do exist on GitHub to Gitea.
+  $github_repos | each {|repo|
+    let url = if not $repo.private {
+      $repo.html_url
+    } else {
+      $"https://($github_token)@github.com/($github_user)/($repo.name)"
     }
 
-    let url = if not $repo_is_private {
-      $url
-    } else {
-      $"https://($github_token)@github.com/($github_user)/($repo_name)"
-    }
-
-    print --no-newline $"(ansi blue)($strategy | str replace "ed" "ing") ([ public private ] | get ($repo_is_private | into int)) repository ($url) to ($gitea_url)/($gitea_user)/($repo_name)..."
+    print --no-newline $"(ansi blue)($strategy | str capitalize | str replace "ed" "ing") ([ public private ] | get ($repo.private | into int)) repository ($url) to ($gitea_url)/($gitea_user)/($repo.name)...(ansi reset)"
 
     let response = (
       http post $"($gitea_url)/api/v1/repos/migrate"
       --allow-errors
       -t application/json
-      -H [
-        Authorization $"token ($gitea_token)"
-      ]
+      -H [ Authorization $"token ($gitea_token)" ]
       {
         clone_addr: $url
         mirror: ($strategy != "cloned")
-        private: $repo_is_private
-        uid: $gitea_uid
+        private: $repo.private
 
         repo_owner: $gitea_user
-        repo_name: $repo_name
+        repo_name: $repo.name
       }
     )
 
     let error_message = ($response | get -i message)
     if ($error_message != null and $error_message =~ "already exists") {
-      print $" (ansi yellow)Already mirrored!"
+      print $" (ansi yellow)Already mirrored!(ansi reset)"
     } else if ($error_message != null) {
-      print $" (ansi red)Unknown error: ($error_message)"
+      print $" (ansi red)Unknown error: ($error_message)(ansi reset)"
     } else {
-      print $" (ansi green)Success!"
+      print $" (ansi green)Success!(ansi reset)"
     }
   }
+
+  null
 }