diff --git a/cmd/enbas/main.go b/cmd/enbas/main.go
index 7739113..2b0b364 100644
--- a/cmd/enbas/main.go
+++ b/cmd/enbas/main.go
@@ -39,7 +39,7 @@ var (
 
 func main() {
 	if err := run(); err != nil {
-		fmt.Fprintf(os.Stderr, "ERROR: %v\n", err)
+		fmt.Fprintf(os.Stderr, "ERROR: %v.\n", err)
 		os.Exit(1)
 	}
 }
diff --git a/internal/executor/errors.go b/internal/executor/errors.go
index 6383ef3..d6650fa 100644
--- a/internal/executor/errors.go
+++ b/internal/executor/errors.go
@@ -9,7 +9,7 @@ type FlagNotSetError struct {
 }
 
 func (e FlagNotSetError) Error() string {
-	return "the flag '" + e.flagText + "' is not set"
+	return "please use the required --" + e.flagText + " flag"
 }
 
 type UnsupportedTypeError struct {
@@ -17,15 +17,7 @@ type UnsupportedTypeError struct {
 }
 
 func (e UnsupportedTypeError) Error() string {
-	return "unsupported resource type '" + e.resourceType + "'"
-}
-
-type InvalidTimelineCategoryError struct {
-	category string
-}
-
-func (e InvalidTimelineCategoryError) Error() string {
-	return "'" + e.category + "' is not a valid timeline category (please choose home, public, tag or list)"
+	return "'" + e.resourceType + "' is not supported for this operation"
 }
 
 type NoAccountSpecifiedError struct{}
@@ -52,9 +44,9 @@ func (e UnsupportedRemoveOperationError) Error() string {
 	return "removing '" + e.ResourceType + "' from '" + e.RemoveFromResourceType + "' is not supported"
 }
 
-type EmptyContentError struct{
+type EmptyContentError struct {
 	ResourceType string
-	Hint string
+	Hint         string
 }
 
 func (e EmptyContentError) Error() string {
diff --git a/internal/executor/show.go b/internal/executor/show.go
index c5930d6..3f1b280 100644
--- a/internal/executor/show.go
+++ b/internal/executor/show.go
@@ -42,7 +42,7 @@ func NewShowExecutor(tlf TopLevelFlags, name, summary string) *ShowExecutor {
 	command.StringVar(&command.resourceType, flagType, "", "specify the type of resource to display")
 	command.StringVar(&command.accountName, flagAccountName, "", "specify the account name in full (username@domain)")
 	command.StringVar(&command.statusID, flagStatusID, "", "specify the ID of the status to display")
-	command.StringVar(&command.timelineCategory, flagTimelineCategory, "home", "specify the type of timeline to display (valid values are home, public, list and tag)")
+	command.StringVar(&command.timelineCategory, flagTimelineCategory, model.TimelineCategoryHome, "specify the timeline category to view")
 	command.StringVar(&command.listID, flagListID, "", "specify the ID of the list to display")
 	command.StringVar(&command.tag, flagTag, "", "specify the name of the tag to use")
 	command.IntVar(&command.limit, flagLimit, 20, "specify the limit of items to display")
@@ -75,7 +75,7 @@ func (c *ShowExecutor) Execute() error {
 
 	gtsClient, err := client.NewClientFromConfig(c.topLevelFlags.ConfigDir)
 	if err != nil {
-		return fmt.Errorf("unable to create the GoToSocial client; %w", err)
+		return fmt.Errorf("unable to create the GoToSocial client: %w", err)
 	}
 
 	return doFunc(gtsClient)
@@ -84,7 +84,7 @@ func (c *ShowExecutor) Execute() error {
 func (c *ShowExecutor) showInstance(gtsClient *client.Client) error {
 	instance, err := gtsClient.GetInstance()
 	if err != nil {
-		return fmt.Errorf("unable to retrieve the instance details; %w", err)
+		return fmt.Errorf("unable to retrieve the instance details: %w", err)
 	}
 
 	utilities.Display(instance, *c.topLevelFlags.NoColor)
@@ -101,7 +101,7 @@ func (c *ShowExecutor) showAccount(gtsClient *client.Client) error {
 	if c.myAccount {
 		account, err = getMyAccount(gtsClient, c.topLevelFlags.ConfigDir)
 		if err != nil {
-			return fmt.Errorf("received an error while getting the account details; %w", err)
+			return fmt.Errorf("received an error while getting the account details: %w", err)
 		}
 	} else {
 		if c.accountName == "" {
@@ -110,7 +110,7 @@ func (c *ShowExecutor) showAccount(gtsClient *client.Client) error {
 
 		account, err = getAccount(gtsClient, c.accountName)
 		if err != nil {
-			return fmt.Errorf("received an error while getting the account details; %w", err)
+			return fmt.Errorf("received an error while getting the account details: %w", err)
 		}
 	}
 
@@ -125,7 +125,7 @@ func (c *ShowExecutor) showAccount(gtsClient *client.Client) error {
 	if !c.myAccount && !c.skipAccountRelationship {
 		relationship, err := gtsClient.GetAccountRelationship(account.ID)
 		if err != nil {
-			return fmt.Errorf("unable to retrieve the relationship to this account; %w", err)
+			return fmt.Errorf("unable to retrieve the relationship to this account: %w", err)
 		}
 
 		utilities.Display(relationship, *c.topLevelFlags.NoColor)
@@ -134,7 +134,7 @@ func (c *ShowExecutor) showAccount(gtsClient *client.Client) error {
 	if c.myAccount && c.showUserPreferences {
 		preferences, err := gtsClient.GetUserPreferences()
 		if err != nil {
-			return fmt.Errorf("unable to retrieve the user preferences; %w", err)
+			return fmt.Errorf("unable to retrieve the user preferences: %w", err)
 		}
 
 		utilities.Display(preferences, *c.topLevelFlags.NoColor)
@@ -150,7 +150,7 @@ func (c *ShowExecutor) showStatus(gtsClient *client.Client) error {
 
 	status, err := gtsClient.GetStatus(c.statusID)
 	if err != nil {
-		return fmt.Errorf("unable to retrieve the status; %w", err)
+		return fmt.Errorf("unable to retrieve the status: %w", err)
 	}
 
 	if c.showInBrowser {
@@ -171,28 +171,28 @@ func (c *ShowExecutor) showTimeline(gtsClient *client.Client) error {
 	)
 
 	switch c.timelineCategory {
-	case "home":
+	case model.TimelineCategoryHome:
 		timeline, err = gtsClient.GetHomeTimeline(c.limit)
-	case "public":
+	case model.TimelineCategoryPublic:
 		timeline, err = gtsClient.GetPublicTimeline(c.limit)
-	case "list":
+	case model.TimelineCategoryList:
 		if c.listID == "" {
 			return FlagNotSetError{flagText: flagListID}
 		}
 
 		timeline, err = gtsClient.GetListTimeline(c.listID, c.limit)
-	case "tag":
+	case model.TimelineCategoryTag:
 		if c.tag == "" {
 			return FlagNotSetError{flagText: flagTag}
 		}
 
 		timeline, err = gtsClient.GetTagTimeline(c.tag, c.limit)
 	default:
-		return InvalidTimelineCategoryError{category: c.timelineCategory}
+		return model.InvalidTimelineCategoryError{Value: c.timelineCategory}
 	}
 
 	if err != nil {
-		return fmt.Errorf("unable to retrieve the %s timeline; %w", c.timelineCategory, err)
+		return fmt.Errorf("unable to retrieve the %s timeline: %w", c.timelineCategory, err)
 	}
 
 	if len(timeline.Statuses) == 0 {
@@ -213,12 +213,12 @@ func (c *ShowExecutor) showList(gtsClient *client.Client) error {
 
 	list, err := gtsClient.GetList(c.listID)
 	if err != nil {
-		return fmt.Errorf("unable to retrieve the list; %w", err)
+		return fmt.Errorf("unable to retrieve the list: %w", err)
 	}
 
 	accounts, err := gtsClient.GetAccountsFromList(c.listID, 0)
 	if err != nil {
-		return fmt.Errorf("unable to retrieve the accounts from the list; %w", err)
+		return fmt.Errorf("unable to retrieve the accounts from the list: %w", err)
 	}
 
 	if len(accounts) > 0 {
@@ -238,7 +238,7 @@ func (c *ShowExecutor) showList(gtsClient *client.Client) error {
 func (c *ShowExecutor) showLists(gtsClient *client.Client) error {
 	lists, err := gtsClient.GetAllLists()
 	if err != nil {
-		return fmt.Errorf("unable to retrieve the lists; %w", err)
+		return fmt.Errorf("unable to retrieve the lists: %w", err)
 	}
 
 	if len(lists) == 0 {
@@ -255,12 +255,12 @@ func (c *ShowExecutor) showLists(gtsClient *client.Client) error {
 func (c *ShowExecutor) showFollowers(gtsClient *client.Client) error {
 	accountID, err := getAccountID(gtsClient, c.myAccount, c.accountName, c.topLevelFlags.ConfigDir)
 	if err != nil {
-		return fmt.Errorf("received an error while getting the account ID; %w", err)
+		return fmt.Errorf("received an error while getting the account ID: %w", err)
 	}
 
 	followers, err := gtsClient.GetFollowers(accountID, c.limit)
 	if err != nil {
-		return fmt.Errorf("unable to retrieve the list of followers; %w", err)
+		return fmt.Errorf("unable to retrieve the list of followers: %w", err)
 	}
 
 	if len(followers.Accounts) > 0 {
@@ -275,12 +275,12 @@ func (c *ShowExecutor) showFollowers(gtsClient *client.Client) error {
 func (c *ShowExecutor) showFollowing(gtsClient *client.Client) error {
 	accountID, err := getAccountID(gtsClient, c.myAccount, c.accountName, c.topLevelFlags.ConfigDir)
 	if err != nil {
-		return fmt.Errorf("received an error while getting the account ID; %w", err)
+		return fmt.Errorf("received an error while getting the account ID: %w", err)
 	}
 
 	following, err := gtsClient.GetFollowing(accountID, c.limit)
 	if err != nil {
-		return fmt.Errorf("unable to retrieve the list of followed accounts; %w", err)
+		return fmt.Errorf("unable to retrieve the list of followed accounts: %w", err)
 	}
 
 	if len(following.Accounts) > 0 {
@@ -295,7 +295,7 @@ func (c *ShowExecutor) showFollowing(gtsClient *client.Client) error {
 func (c *ShowExecutor) showBlocked(gtsClient *client.Client) error {
 	blocked, err := gtsClient.GetBlockedAccounts(c.limit)
 	if err != nil {
-		return fmt.Errorf("unable to retrieve the list of blocked accounts; %w", err)
+		return fmt.Errorf("unable to retrieve the list of blocked accounts: %w", err)
 	}
 
 	if len(blocked.Accounts) > 0 {
diff --git a/internal/model/timeline.go b/internal/model/timeline.go
index d58e519..dff1d5e 100644
--- a/internal/model/timeline.go
+++ b/internal/model/timeline.go
@@ -10,6 +10,27 @@ import (
 	"codeflow.dananglin.me.uk/apollo/enbas/internal/utilities"
 )
 
+const (
+	TimelineCategoryHome   = "home"
+	TimelineCategoryPublic = "public"
+	TimelineCategoryTag    = "tag"
+	TimelineCategoryList   = "list"
+)
+
+type InvalidTimelineCategoryError struct {
+	Value string
+}
+
+func (e InvalidTimelineCategoryError) Error() string {
+	return "'" +
+		e.Value +
+		"' is not a valid timeline category (valid values are " +
+		TimelineCategoryHome + ", " +
+		TimelineCategoryPublic + ", " +
+		TimelineCategoryTag + ", " +
+		TimelineCategoryList + ")"
+}
+
 type Timeline struct {
 	Name     string
 	Statuses []Status