diff --git a/README.md b/README.md
index 8563d05..67c85a9 100644
--- a/README.md
+++ b/README.md
@@ -18,16 +18,16 @@ This plugin assumes that the mapping of "_which Image tag should be deployed to
 
 ## Variables
 
-| Variable name    | Variable meaning                                                                                                                                                                                      | Example value                                                                    |
-|------------------|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|----------------------------------------------------------------------------------|
-| BRANCH           | The branch of the Infrastructure Repo on which to make a commit                                                                                                                                       | `main`                                                                           |
-| GIT_REPO         | The (https://) address of the Infrastructure Repo                                                                                                                                                     | `https://github.com/myusername/coolrepo`                                         |
-| IMAGE_TAG        | The Image Tag to insert into a tracking file                                                                                                                                                          | `a6b6e8`                                                                         |
-| DESTINATION_FILE | The file in Infrastructure Repo that should be updated to contain `IMAGE_TAG`                                                                                                                         | `deployed_tags/prod_image_tag`                                                   |
-| AUTHOR_EMAIL     | The email that should be associated with the automated commit                                                                                                                                         | `myname@gmail.com`                                                               |
-| AUTHOR_NAME      | The name that should be associated with the automated commit                                                                                                                                          | `Adam Nonymous`                                                                  |
-| COMMIT_MESSAGE   | Commit message. Expands environment variables ([note that](https://docs.drone.io/plugins/overview/#plugin-inputs) any of these variables should have `PLUGIN_` prepended if you are referencing them) | `[Auto] Automated commit to write $PLUGIN_IMAGE_TAG to $PLUGIN_DESTINATION_FILE` |
-| ACCESS_TOKEN     | Personal Access Token providing access to the Git Repo                                                                                                                                                | <PAT>                                                                            |
+| Variable name    | Required? | Variable meaning                                                                                                                                                                                      | Example value (default value for optional variables) |
+|------------------|-----------|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|------------------------------------------------------|
+| BRANCH           | No        | The branch of the Infrastructure Repo on which to make a commit                                                                                                                                       | `main`                                               |
+| AUTHOR_EMAIL     | No        | The email that should be associated with the automated commit                                                                                                                                         | `auto-update-bot@example.com`                        |
+| AUTHOR_NAME      | No        | The name that should be associated with the automated commit                                                                                                                                          | `Auto Update Bot`                                    |
+| COMMIT_MESSAGE   | No        | Commit message. Expands environment variables ([note that](https://docs.drone.io/plugins/overview/#plugin-inputs) any of these variables should have `PLUGIN_` prepended if you are referencing them) | `[Auto] Update $DESTINATION_FILE to $IMAGE_TAG`      |
+| GIT_REPO         | Yes       | The (https://) address of the Infrastructure Repo                                                                                                                                                     | `https://github.com/myusername/coolrepo`             |
+| IMAGE_TAG        | Yes       | The Image Tag to insert into a tracking file                                                                                                                                                          | `a6b6e8`                                             |
+| DESTINATION_FILE | Yes       | The file in Infrastructure Repo that should be updated to contain `IMAGE_TAG`                                                                                                                         | `deployed_tags/prod_image_tag`                       |
+| ACCESS_TOKEN     | Yes       | Personal Access Token providing access to the Git Repo                                                                                                                                                | <PAT>                                                |
 
 # FAQs
 
diff --git a/script.sh b/script.sh
index 1b5544d..65f70a5 100644
--- a/script.sh
+++ b/script.sh
@@ -2,6 +2,12 @@
 
 set -eox pipefail
 
+# Set default values
+PLUGIN_BRANCH="${PLUGIN_BRANCH:=main}"
+PLUGIN_AUTHOR_EMAIL="${PLUGIN_AUTHOR_EMAIL:=auto-update-bot@example.com}"
+PLUGIN_AUTHOR_NAME="${PLUGIN_AUTHOR_NAME:=Auto Update Bot}"
+PLUGIN_COMMIT_MESSAGE="${PLUGIN_COMMIT_MESSAGE:=[Auto] Update $PLUGIN_DESTINATION_FILE to $PLUGIN_IMAGE_TAG}"
+
 mkdir /working
 cd /working
 git clone -b "$PLUGIN_BRANCH" "$PLUGIN_GIT_REPO" .