diff --git a/pkg/api/http_client.go b/pkg/api/http_client.go
index 03095bf..8490267 100644
--- a/pkg/api/http_client.go
+++ b/pkg/api/http_client.go
@@ -8,16 +8,11 @@ import (
 	"time"
 )
 
-const (
-	BaseURLPro  = "https://api.deepl.com/v2"
-	BaseURLFree = "https://api-free.deepl.com/v2"
-)
-
 type Client struct {
 	httpClient *http.Client
 }
 
-func NewClient(baseURL string, authKey string, timeout time.Duration) *Client {
+func NewClient(timeout time.Duration) *Client {
 	client := &http.Client{
 		Timeout: timeout,
 	}
diff --git a/pkg/api/translate.go b/pkg/api/translate.go
index 0e53eb4..57d1389 100644
--- a/pkg/api/translate.go
+++ b/pkg/api/translate.go
@@ -4,6 +4,8 @@ import (
 	"encoding/json"
 	"net/http"
 	"net/url"
+
+	"github.com/pkg/errors"
 )
 
 type Translation struct {
@@ -11,80 +13,101 @@ type Translation struct {
 	Text                   string `json:"text"`
 }
 
+// TranslateOption is a functional option for configuring text translation parameters
 type TranslateOption func(url.Values)
 
 // The language to be translated.
-// If this parameter is omitted, the API will attempt to detect the language of the text and translate it.
-func SourceLang(lang string) TranslateOption {
+// If this parameter is omitted, the API will attempt to detect the language of the text and translate it
+func SourceLang(lang string) (TranslateOption, error) {
 	return func(vals url.Values) {
 		vals.Set("source_lang", lang)
-	}
+	}, nil
 }
 
-// Sets whether the translation engine should first split the input into sentences.
-func SplitSentences(split string) TranslateOption {
-	return func(vals url.Values) {
-		vals.Set("split_sentences", split)
+// SplitSentences sets whether the translation engine should first split the input into sentences
+func SplitSentences(split string) (TranslateOption, error) {
+	switch split {
+	case "0", "1", "nonewlines":
+		return func(vals url.Values) {
+			vals.Set("split_sentences", split)
+		}, nil
 	}
+	return nil, errors.Errorf("Invalid SplitSentence value: %s", split)
 }
 
-// Sets whether the translation engine should respect the original formatting, even if it would usually correct some aspects.
-func PreserveFormatting(preserve string) TranslateOption {
-	return func(vals url.Values) {
-		vals.Set("preserve_formatting", preserve)
+// PreserveFormatting sets whether the translation engine should respect the original formatting, even if it would usually correct some aspects
+func PreserveFormatting(preserve string) (TranslateOption, error) {
+	switch preserve {
+	case "0", "1":
+		return func(vals url.Values) {
+			vals.Set("preserve_formatting", preserve)
+		}, nil
 	}
+	return errors.Errorf("Invalid PreserveFormatting value: %s", preserve)
 }
 
-// Sets whether the translated text should lean towards formal or informal language.
-func Formality(formality string) TranslateOption {
-	return func(vals url.Values) {
-		vals.Set("formality", formality)
+// Formality sets whether the translated text should lean towards formal or informal language
+func Formality(formality string) (TranslateOption, error) {
+	switch formality {
+	case "default", "more", "less", "prefer_more", "prefer_less":
+		return func(vals url.Values) {
+			vals.Set("formality", formality)
+		}, nil
 	}
+	return nil, errors.Errorf("Invalid Formality value: %s", formality)
 }
 
-// Specify the glossary to use for the translation.
-func GlossaryId(glossary string) TranslateOption {
+// GlossaryId specifies the glossary to use for the translation
+func GlossaryId(glossary string) (TranslateOption, error) {
 	return func(vals url.Values) {
 		vals.Set("glossary_id", glossary)
-	}
+	}, nil
 }
 
-// Sets which kind of tags should be handled.
-func TagHandling(handling string) TranslateOption {
-	return func(vals url.Values) {
-		vals.Set("tag_handling", handling)
+// TagHandling sets which kind of tags should be handled
+func TagHandling(handling string) (TranslateOption, error) {
+	switch handling {
+	case "html", "xml":
+		return func(vals url.Values) {
+			vals.Set("tag_handling", handling)
+		}, nil
 	}
+	return nil, errors.Errorf("Invalid TagHandling value: %s", handling)
 }
 
-// Comma-separated list of XML tags which never split sentences.
-func NonSplittingTags(tags string) TranslateOption {
+// NonSplittingTags specifies a comma-separated list of XML tags which never split sentences
+func NonSplittingTags(tags string) (TranslateOption, error) {
 	return func(vals url.Values) {
 		vals.Set("non_splitting_tags", tags)
-	}
+	}, nil
 }
 
-// Disable the automatic detection of the XML structure.
-func OutlineDetection(detect string) TranslateOption {
-	return func(vals url.Values) {
-		vals.Set("outline_detection", detect)
+// OutlineDetection can be used to disable the automatic detection of the XML structure
+func OutlineDetection(detect string) (TranslateOption, error) {
+	switch detect {
+	case "0":
+		return func(vals url.Values) {
+			vals.Set("outline_detection", detect)
+		}, nil
 	}
+	return nil, errors.Errorf("Invalid OutlineDetection value: %s", detect)
 }
 
-// Comma-separated list of XML tags which always cause splts.
-func SplittingTags(tags string) TranslateOption {
+// SplittingTags specifies a comma-separated list of XML tags which always cause splts
+func SplittingTags(tags string) (TranslateOption, error) {
 	return func(vals url.Values) {
 		vals.Set("splitting_tags", tags)
-	}
+	}, nil
 }
 
-// Comma-separated list of XML tags that indicate text not to be translated.
-func IgnoreTags(tags string) TranslateOption {
+// IgnoeTags specifies a comma-separated list of XML tags that indicate text not to be translated
+func IgnoreTags(tags string) (TranslateOption, error) {
 	return func(vals url.Values) {
 		vals.Set("ignore_tags", tags)
-	}
+	}, nil
 }
 
-// The translate function.
+// TranslateText translates the given text(s) into the specified target language
 func (t *Translator) TranslateText(texts []string, targetLang string, options ...TranslateOption) ([]Translation, error) {
 	vals := make(url.Values)
 
@@ -94,6 +117,7 @@ func (t *Translator) TranslateText(texts []string, targetLang string, options ..
 
 	vals.Set("target_lang", targetLang)
 
+	// Apply translation parameter options
 	for _, opt := range options {
 		opt(vals)
 	}
diff --git a/pkg/api/translator.go b/pkg/api/translator.go
index 04c53be..156512f 100644
--- a/pkg/api/translator.go
+++ b/pkg/api/translator.go
@@ -8,9 +8,10 @@ import (
 	"time"
 )
 
-type TranslatorOptions struct {
-	ServerUrl string `default:""`
-}
+const (
+	ServerURLPro  = "https://api.deepl.com/v2"
+	ServerURLFree = "https://api-free.deepl.com/v2"
+)
 
 type Translator struct {
 	httpClient *Client
@@ -18,26 +19,58 @@ type Translator struct {
 	authKey    string
 }
 
-func NewTranslator(authKey string, options TranslatorOptions) *Translator {
-	var serverURL string
-	if options.ServerUrl == "" {
-		if authKeyIsFreeAccount(authKey) {
-			serverURL = BaseURLFree
-		} else {
-			serverURL = BaseURLPro
+// TranslatorOption is a functional option for configuring the Translator
+type TranslatorOption func(*Translator) error
+
+// ServerURL allows overriding the default server url
+func ServerURL(url string) TranslatorOption {
+	return func(t *Translator) error {
+		t.serverURL = url
+		return nil
+	}
+}
+
+// parseOptions apllies the supplied functional options to the Translator
+func (t *Translator) parseOptions(opts ...TranslatorOption) error {
+	for _, opt := range opts {
+		err := opt(t)
+		if err != nil {
+			return err
 		}
 	}
 
-	timeout := 10 * time.Second
-	httpClient := NewClient(serverURL, authKey, timeout)
+	return nil
+}
 
-	return &Translator{
+// NewTranslator creates a new translator
+func NewTranslator(authKey string, opts ...TranslatorOption) (*Translator, error) {
+	// Determine default server url based on auth key
+	var serverURL string
+	if authKeyIsFreeAccount(authKey) {
+		serverURL = ServerURLFree
+	} else {
+		serverURL = ServerURLPro
+	}
+
+	// Set up default http client
+	timeout := time.Second * 30
+	httpClient := NewClient(timeout)
+
+	t := &Translator{
 		httpClient: httpClient,
 		serverURL:  serverURL,
 		authKey:    authKey,
 	}
+
+	// Parse and apply options
+	if err := t.parseOptions(opts...); err != nil {
+		return nil, err
+	}
+
+	return t, nil
 }
 
+// callAPI calls the supplied API endpoint with the provided parameters and returns the response
 func (t *Translator) callAPI(method string, endpoint string, data url.Values, headers http.Header) (*http.Response, error) {
 	url := fmt.Sprintf("%s/%s", t.serverURL, endpoint)
 
@@ -54,6 +87,7 @@ func (t *Translator) callAPI(method string, endpoint string, data url.Values, he
 	return res, err
 }
 
+// authKeyIsFreeAccount determines whether the supplied auth key belongs to a Free account
 func authKeyIsFreeAccount(authKey string) bool {
 	return strings.HasSuffix(authKey, ":fx")
 }