diff --git a/internal/chatgpt/chatgpt.go b/internal/chatgpt/chatgpt.go
index 714c046..445400f 100644
--- a/internal/chatgpt/chatgpt.go
+++ b/internal/chatgpt/chatgpt.go
@@ -10,6 +10,10 @@ import (
 	"github.com/dfanso/commit-msg/pkg/types"
 )
 
+const (
+	chatgptModel = openai.ChatModelGPT4o
+)
+
 // GenerateCommitMessage calls OpenAI's chat completions API to turn the provided
 // repository changes into a polished git commit message.
 func GenerateCommitMessage(config *types.Config, changes string, apiKey string, opts *types.GenerationOptions) (string, error) {
@@ -22,7 +26,7 @@ func GenerateCommitMessage(config *types.Config, changes string, apiKey string,
 		Messages: []openai.ChatCompletionMessageParamUnion{
 			openai.UserMessage(prompt),
 		},
-		Model: openai.ChatModelGPT4o,
+		Model: chatgptModel,
 	})
 	if err != nil {
 		return "", fmt.Errorf("OpenAI error: %w", err)
diff --git a/internal/claude/claude.go b/internal/claude/claude.go
index c4aefbc..c93a00a 100644
--- a/internal/claude/claude.go
+++ b/internal/claude/claude.go
@@ -11,6 +11,16 @@ import (
 	"github.com/dfanso/commit-msg/pkg/types"
 )
 
+const (
+	claudeModel        = "claude-3-5-sonnet-20241022"
+	claudeMaxTokens    = 200
+	claudeAPIEndpoint  = "https://api.anthropic.com/v1/messages"
+	claudeAPIVersion   = "2023-06-01"
+	contentTypeJSON    = "application/json"
+	anthropicVersionHeader = "anthropic-version"
+	xAPIKeyHeader      = "x-api-key"
+)
+
 // ClaudeRequest describes the payload sent to Anthropic's Claude messages API.
 type ClaudeRequest struct {
 	Model     string          `json:"model"`
@@ -34,8 +44,8 @@ func GenerateCommitMessage(config *types.Config, changes string, apiKey string,
 	prompt := types.BuildCommitPrompt(changes, opts)
 
 	reqBody := ClaudeRequest{
-		Model:     "claude-3-5-sonnet-20241022",
-		MaxTokens: 200,
+		Model:     claudeModel,
+		MaxTokens: claudeMaxTokens,
 		Messages: []types.Message{
 			{
 				Role:    "user",
@@ -50,14 +60,14 @@ func GenerateCommitMessage(config *types.Config, changes string, apiKey string,
 	}
 
 	ctx := context.Background()
-	req, err := http.NewRequestWithContext(ctx, "POST", "https://api.anthropic.com/v1/messages", bytes.NewBuffer(jsonData))
+	req, err := http.NewRequestWithContext(ctx, "POST", claudeAPIEndpoint, bytes.NewBuffer(jsonData))
 	if err != nil {
 		return "", err
 	}
 
-	req.Header.Set("Content-Type", "application/json")
-	req.Header.Set("x-api-key", apiKey)
-	req.Header.Set("anthropic-version", "2023-06-01")
+	req.Header.Set("Content-Type", contentTypeJSON)
+	req.Header.Set(xAPIKeyHeader, apiKey)
+	req.Header.Set(anthropicVersionHeader, claudeAPIVersion)
 
 	client := httpClient.GetClient()
 	resp, err := client.Do(req)
diff --git a/internal/gemini/gemini.go b/internal/gemini/gemini.go
index 0606d49..3d8146d 100644
--- a/internal/gemini/gemini.go
+++ b/internal/gemini/gemini.go
@@ -10,6 +10,11 @@ import (
 	"github.com/dfanso/commit-msg/pkg/types"
 )
 
+const (
+	geminiModel       = "gemini-2.0-flash"
+	geminiTemperature = 0.2
+)
+
 // GenerateCommitMessage asks Google Gemini to author a commit message for the
 // supplied repository changes and optional style instructions.
 func GenerateCommitMessage(config *types.Config, changes string, apiKey string, opts *types.GenerationOptions) (string, error) {
@@ -25,8 +30,8 @@ func GenerateCommitMessage(config *types.Config, changes string, apiKey string,
 	defer client.Close()
 
 	// Create a GenerativeModel with appropriate settings
-	model := client.GenerativeModel("gemini-2.0-flash")
-	model.SetTemperature(0.2) // Lower temperature for more focused responses
+	model := client.GenerativeModel(geminiModel)
+	model.SetTemperature(geminiTemperature) // Lower temperature for more focused responses
 
 	// Generate content using the prompt
 	resp, err := model.GenerateContent(ctx, genai.Text(prompt))
diff --git a/internal/grok/grok.go b/internal/grok/grok.go
index 7a42960..d86e784 100644
--- a/internal/grok/grok.go
+++ b/internal/grok/grok.go
@@ -11,6 +11,14 @@ import (
 	"github.com/dfanso/commit-msg/pkg/types"
 )
 
+const (
+	grokModel          = "grok-3-mini-fast-beta"
+	grokTemperature    = 0
+	grokAPIEndpoint    = "https://api.x.ai/v1/chat/completions"
+	grokContentType    = "application/json"
+	authorizationPrefix = "Bearer "
+)
+
 // GenerateCommitMessage calls X.AI's Grok API to create a commit message from
 // the provided Git diff and generation options.
 func GenerateCommitMessage(config *types.Config, changes string, apiKey string, opts *types.GenerationOptions) (string, error) {
@@ -25,9 +33,9 @@ func GenerateCommitMessage(config *types.Config, changes string, apiKey string,
 				Content: prompt,
 			},
 		},
-		Model:       "grok-3-mini-fast-beta",
+		Model:       grokModel,
 		Stream:      false,
-		Temperature: 0,
+		Temperature: grokTemperature,
 	}
 
 	requestBody, err := json.Marshal(request)
@@ -36,14 +44,14 @@ func GenerateCommitMessage(config *types.Config, changes string, apiKey string,
 	}
 
 	// Create HTTP request
-	req, err := http.NewRequest("POST", "https://api.x.ai/v1/chat/completions", bytes.NewBuffer(requestBody))
+	req, err := http.NewRequest("POST", grokAPIEndpoint, bytes.NewBuffer(requestBody))
 	if err != nil {
 		return "", err
 	}
 
 	// Set headers
-	req.Header.Set("Content-Type", "application/json")
-	req.Header.Set("Authorization", fmt.Sprintf("Bearer %s", apiKey))
+	req.Header.Set("Content-Type", grokContentType)
+	req.Header.Set("Authorization", fmt.Sprintf("%s%s", authorizationPrefix, apiKey))
 
 	client := httpClient.GetClient()
 	resp, err := client.Do(req)
diff --git a/internal/groq/groq.go b/internal/groq/groq.go
index 013dd0e..4630fb8 100644
--- a/internal/groq/groq.go
+++ b/internal/groq/groq.go
@@ -36,6 +36,14 @@ type chatResponse struct {
 // If Groq updates their defaults again, override via GROQ_MODEL.
 const defaultModel = "llama-3.3-70b-versatile"
 
+const (
+	groqTemperature         = 0.2
+	groqMaxTokens           = 200
+	groqSystemMessage       = "You are an assistant that writes clear, concise git commit messages."
+	groqContentType         = "application/json"
+	groqAuthorizationPrefix = "Bearer "
+)
+
 var (
 	// allow overrides in tests
 	baseURL = "https://api.groq.com/openai/v1/chat/completions"
@@ -62,10 +70,10 @@ func GenerateCommitMessage(_ *types.Config, changes string, apiKey string, opts
 
 	payload := chatRequest{
 		Model:       model,
-		Temperature: 0.2,
-		MaxTokens:   200,
+		Temperature: groqTemperature,
+		MaxTokens:   groqMaxTokens,
 		Messages: []chatMessage{
-			{Role: "system", Content: "You are an assistant that writes clear, concise git commit messages."},
+			{Role: "system", Content: groqSystemMessage},
 			{Role: "user", Content: prompt},
 		},
 	}
@@ -85,8 +93,8 @@ func GenerateCommitMessage(_ *types.Config, changes string, apiKey string, opts
 		return "", fmt.Errorf("failed to create Groq request: %w", err)
 	}
 
-	req.Header.Set("Content-Type", "application/json")
-	req.Header.Set("Authorization", fmt.Sprintf("Bearer %s", apiKey))
+	req.Header.Set("Content-Type", groqContentType)
+	req.Header.Set("Authorization", fmt.Sprintf("%s%s", groqAuthorizationPrefix, apiKey))
 
 	resp, err := httpClient.Do(req)
 	if err != nil {
diff --git a/internal/ollama/ollama.go b/internal/ollama/ollama.go
index 98f354b..0db08c9 100644
--- a/internal/ollama/ollama.go
+++ b/internal/ollama/ollama.go
@@ -11,6 +11,12 @@ import (
 	"github.com/dfanso/commit-msg/pkg/types"
 )
 
+const (
+	ollamaDefaultModel = "llama3:latest"
+	ollamaStream       = false
+	ollamaContentType  = "application/json"
+)
+
 // OllamaRequest captures the prompt payload sent to an Ollama HTTP endpoint.
 type OllamaRequest struct {
 	Model  string `json:"model"`
@@ -28,7 +34,7 @@ type OllamaResponse struct {
 func GenerateCommitMessage(_ *types.Config, changes string, url string, model string, opts *types.GenerationOptions) (string, error) {
 	// Use llama3:latest as the default model
 	if model == "" {
-		model = "llama3:latest"
+		model = ollamaDefaultModel
 	}
 
 	// Preparing the prompt
@@ -38,7 +44,7 @@ func GenerateCommitMessage(_ *types.Config, changes string, url string, model st
 	reqBody := map[string]interface{}{
 		"model":  model,
 		"prompt": prompt,
-		"stream": false,
+		"stream": ollamaStream,
 	}
 
 	// Generating the body
@@ -51,7 +57,7 @@ func GenerateCommitMessage(_ *types.Config, changes string, url string, model st
 	if err != nil {
 		return "", fmt.Errorf("failed to create request: %v", err)
 	}
-	req.Header.Set("Content-Type", "application/json")
+	req.Header.Set("Content-Type", ollamaContentType)
 
 	resp, err := httpClient.GetOllamaClient().Do(req)
 	if err != nil {