diff --git a/COMMITS.md b/COMMITS.md
index 2b4ba45..d93ea10 100644
--- a/COMMITS.md
+++ b/COMMITS.md
@@ -2,7 +2,7 @@ This style guide is used chiefly to test that aicommit follows the
 style guide.
 
 * Only provide a multi-line message when the change is non-trivial.
-* For example, a few lines changed is trivial. Prefer a single-line message.
-* Most changes under 100 lines changed are trivial and only need a single-line
-  message.
-* Never begin the commit with an emoji
\ No newline at end of file
+* For example, a few lines change is trivial. Prefer a single-line message.
+* Most changes under 100 lines changed are trivial and only need a single-line message.
+* Never begin the commit with an emoji.
+* Mind standard Conventional Commits v1.0.0 using most appropriate type.
diff --git a/cmd/aicommit/lint.go b/cmd/aicommit/lint.go
new file mode 100644
index 0000000..9b58aa5
--- /dev/null
+++ b/cmd/aicommit/lint.go
@@ -0,0 +1,95 @@
+package main
+
+import (
+	"errors"
+	"fmt"
+	"io"
+	"os"
+	"strings"
+
+	"github.com/coder/aicommit"
+	"github.com/coder/serpent"
+	"github.com/sashabaranov/go-openai"
+)
+
+func lint(inv *serpent.Invocation, opts runOptions) error {
+	workdir, err := os.Getwd()
+	if err != nil {
+		return err
+	}
+
+	// Build linting prompt considering role, style guide, commit message
+	msgs, err := aicommit.BuildLintPrompt(inv.Stdout, workdir, opts.lint)
+	if err != nil {
+		return err
+	}
+	if len(opts.context) > 0 {
+		msgs = append(msgs, openai.ChatCompletionMessage{
+			Role: openai.ChatMessageRoleSystem,
+			Content: "The user has provided additional context that MUST be" +
+				" included in the commit message",
+		})
+		for _, context := range opts.context {
+			msgs = append(msgs, openai.ChatCompletionMessage{
+				Role:    openai.ChatMessageRoleUser,
+				Content: context,
+			})
+		}
+	}
+
+	ctx := inv.Context()
+	if debugMode {
+		for _, msg := range msgs {
+			debugf("%s (%v tokens)\n%s\n", msg.Role, aicommit.CountTokens(msg), msg.Content)
+		}
+	}
+
+	// Stream AI response
+	stream, err := opts.client.CreateChatCompletionStream(ctx, openai.ChatCompletionRequest{
+		Model:       opts.model,
+		Stream:      true,
+		Temperature: 0,
+		StreamOptions: &openai.StreamOptions{
+			IncludeUsage: true,
+		},
+		Messages: msgs,
+	})
+	if err != nil {
+		return err
+	}
+	defer stream.Close()
+
+	var validationFailed bool
+
+	for {
+		resp, err := stream.Recv()
+		if err != nil {
+			if errors.Is(err, io.EOF) {
+				debugf("stream EOF")
+				break
+			}
+			return err
+		}
+
+		if len(resp.Choices) > 0 {
+			c := resp.Choices[0].Delta.Content
+			inv.Stdout.Write([]byte(c))
+
+			if strings.HasPrefix(c, "❌") {
+				validationFailed = true
+			}
+		} else {
+			inv.Stdout.Write([]byte("\n"))
+		}
+
+		// Usage is only sent in the last message.
+		if resp.Usage != nil {
+			debugf("total tokens: %d", resp.Usage.TotalTokens)
+		}
+	}
+
+	if validationFailed {
+		return fmt.Errorf("validation failed")
+	}
+	return nil
+}
diff --git a/cmd/aicommit/main.go b/cmd/aicommit/main.go
index dcfb210..9ca14ba 100644
--- a/cmd/aicommit/main.go
+++ b/cmd/aicommit/main.go
@@ -199,6 +199,7 @@ type runOptions struct {
 	dryRun        bool
 	amend         bool
 	ref           string
+	lint          string
 	context       []string
 }
 
@@ -261,6 +262,11 @@ func main() {
 			if len(inv.Args) > 0 {
 				opts.ref = inv.Args[0]
 			}
+
+			if opts.lint != "" {
+				return lint(inv, opts)
+			}
+
 			return run(inv, opts)
 		},
 		Options: []serpent.Option{
@@ -308,6 +314,12 @@ func main() {
 				Description:   "Amend the last commit.",
 				Value:         serpent.BoolOf(&opts.amend),
 			},
+			{
+				Name:        "lint",
+				Description: "Lint the commit message.",
+				Flag:        "lint",
+				Value:       serpent.StringOf(&opts.lint),
+			},
 			{
 				Name:          "context",
 				Description:   "Extra context beyond the diff to consider when generating the commit message.",
diff --git a/prompt.go b/prompt.go
index 820ed47..82df210 100644
--- a/prompt.go
+++ b/prompt.go
@@ -152,16 +152,6 @@ func BuildPrompt(
 		},
 	}
 
-	gitRoot, err := findGitRoot(dir)
-	if err != nil {
-		return nil, fmt.Errorf("find git root: %w", err)
-	}
-
-	repo, err := git.PlainOpen(gitRoot)
-	if err != nil {
-		return nil, fmt.Errorf("open repo %q: %w", dir, err)
-	}
-
 	var buf bytes.Buffer
 	// Get the working directory diff
 	if err := generateDiff(&buf, dir, commitHash, amend); err != nil {
@@ -182,10 +172,11 @@ func BuildPrompt(
 
 	targetDiffString := buf.String()
 
-	// Get the HEAD reference
-	head, err := repo.Head()
+	commitMsgs, err := commitMessages(dir, commitHash)
 	if err != nil {
-		// No commits yet
+		return nil, fmt.Errorf("can't read commit messages: %w", err)
+	}
+	if len(commitMsgs) == 0 {
 		fmt.Fprintln(log, "no commits yet")
 		resp = append(resp, openai.ChatCompletionMessage{
 			Role:    openai.ChatMessageRoleUser,
@@ -194,46 +185,6 @@ func BuildPrompt(
 		return resp, nil
 	}
 
-	// Create a log options struct
-	logOptions := &git.LogOptions{
-		From:  head.Hash(),
-		Order: git.LogOrderCommitterTime,
-	}
-
-	// Get the commit iterator
-	commitIter, err := repo.Log(logOptions)
-	if err != nil {
-		return nil, fmt.Errorf("get commit iterator: %w", err)
-	}
-	defer commitIter.Close()
-
-	// Collect the last N commits
-	var commits []*object.Commit
-	for i := 0; i < 300; i++ {
-		commit, err := commitIter.Next()
-		if err == io.EOF {
-			break
-		}
-		if err != nil {
-			return nil, fmt.Errorf("iterate commits: %w", err)
-		}
-		// Ignore if commit equals ref, because we are trying to recalculate
-		// that particular commit's message.
-		if commit.Hash.String() == commitHash {
-			continue
-		}
-		commits = append(commits, commit)
-
-	}
-
-	// We want to reverse the commits so that the most recent commit is the
-	// last or "most recent" in the chat.
-	reverseSlice(commits)
-
-	var commitMsgs []string
-	for _, commit := range commits {
-		commitMsgs = append(commitMsgs, Ellipse(commit.Message, 1000))
-	}
 	// We provide the commit messages in case the actual commit diffs are cut
 	// off due to token limits.
 	resp = append(resp, openai.ChatCompletionMessage{
@@ -276,6 +227,159 @@ func BuildPrompt(
 	return resp, nil
 }
 
+func BuildLintPrompt(log io.Writer, dir, commitMessage string) ([]openai.ChatCompletionMessage, error) {
+	resp := []openai.ChatCompletionMessage{
+		// Describe the role
+		{
+			Role: openai.ChatMessageRoleSystem,
+			Content: strings.Join([]string{
+				"You are `aicommit`, a commit title linting tool.",
+				"You are currently operating in PR title linting mode with access to repository history to ensure consistency.",
+				"Rules to follow:",
+				"1. Apply the repository's style guide strictly. Do not assume beyond the explicit rules provided.",
+				"2. Generate a linting report formatted as follows:",
+				"  * Prefix each line:",
+				"    * ✅ for passed rules",
+				"    * ❌ for violated rules",
+				"    * 🤫 for non-applicable rules, appending (non-applicable).",
+				"  * Include all rules in the report. Do not skip any.",
+				"3. If violations occur, suggest a single corrected PR title prefixed with `suggestion`: (plain text, no code formatting). If no violations exist, skip the suggestion.",
+				"4. Only output the report and suggestion. Avoid any additional text or explanations for the suggestion.",
+			}, "\n"),
+		},
+		// Output example
+		{
+			Role: openai.ChatMessageRoleSystem,
+			Content: strings.Join([]string{
+				"Output Example:",
+				"",
+				"Negative Report",
+				"❌ Rule 1: Limit the subject line to 50 characters.",
+				"✅ Rule 2: Use the imperative mood.",
+				"✅ Rule 3: Capitalize subject and omit period.",
+				"🤫 Rule 5: Include a body only if necessary. (non-applicable)",
+				"",
+				"suggestion: fix: reduce false positives in GetWorkspacesEligibleForTransition",
+			}, "\n"),
+		},
+	}
+
+	// Describe style guide rules
+	styleGuide, err := readStyleGuide(dir)
+	if err != nil {
+		return nil, err
+	}
+	resp = append(resp, openai.ChatCompletionMessage{
+		Role: openai.ChatMessageRoleSystem,
+		Content: strings.Join([]string{
+			"Style Guide Rules:",
+			styleGuide,
+		}, "\n"),
+	})
+
+	// Previous commit messages
+	commitMsgs, err := commitMessages(dir, "")
+	if err != nil {
+		return nil, fmt.Errorf("can't read commit messages: %w", err)
+	}
+	if len(commitMsgs) == 0 {
+		resp = append(resp, openai.ChatCompletionMessage{
+			Role:    openai.ChatMessageRoleUser,
+			Content: "No commits in the repository yet.",
+		})
+	} else {
+		resp = append(resp, openai.ChatCompletionMessage{
+			Role: openai.ChatMessageRoleSystem,
+			Content: "Here are recent commit messages in the same repository:\n" +
+				mustJSON(commitMsgs),
+		},
+		)
+	}
+
+	// Provide commit message to lint
+	resp = append(resp, openai.ChatCompletionMessage{
+		Role:    openai.ChatMessageRoleSystem,
+		Content: "Commit Message to Lint:\n" + commitMessage,
+	})
+	return resp, nil
+}
+
+func readStyleGuide(dir string) (string, error) {
+	styleGuide, err := findRepoStyleGuide(dir)
+	if err != nil {
+		return "", fmt.Errorf("find repository style guide: %w", err)
+	} else if styleGuide != "" {
+		return styleGuide, nil
+	}
+
+	styleGuide, err = findUserStyleGuide()
+	if err != nil {
+		return "", fmt.Errorf("find user style guide: %w", err)
+	} else if styleGuide != "" {
+		return styleGuide, nil
+	}
+	return defaultUserStyleGuide, nil
+}
+
+func commitMessages(dir string, commitHash string) ([]string, error) {
+	gitRoot, err := findGitRoot(dir)
+	if err != nil {
+		return nil, fmt.Errorf("find Git root: %w", err)
+	}
+
+	repo, err := git.PlainOpen(gitRoot)
+	if err != nil {
+		return nil, fmt.Errorf("open repository %q: %w", dir, err)
+	}
+
+	// Get the HEAD reference
+	head, err := repo.Head()
+	if err != nil {
+		return nil, nil // no commits yet
+	}
+
+	// Create a log options struct
+	logOptions := &git.LogOptions{
+		From:  head.Hash(),
+		Order: git.LogOrderCommitterTime,
+	}
+
+	// Get the commit iterator
+	commitIter, err := repo.Log(logOptions)
+	if err != nil {
+		return nil, fmt.Errorf("get commit iterator: %w", err)
+	}
+	defer commitIter.Close()
+
+	// Collect the last N commits
+	var commits []*object.Commit
+	for i := 0; i < 300; i++ {
+		commit, err := commitIter.Next()
+		if err == io.EOF {
+			break
+		}
+		if err != nil {
+			return nil, fmt.Errorf("iterate commits: %w", err)
+		}
+		// Ignore if commit equals ref, because we are trying to recalculate
+		// that particular commit's message.
+		if commitHash != "" && commit.Hash.String() == commitHash {
+			continue
+		}
+		commits = append(commits, commit)
+	}
+
+	// We want to reverse the commits so that the most recent commit is the
+	// last or "most recent" in the chat.
+	reverseSlice(commits)
+
+	var msgs []string
+	for _, commit := range commits {
+		msgs = append(msgs, Ellipse(commit.Message, 1000))
+	}
+	return msgs, nil
+}
+
 // generateDiff uses the git CLI to generate a diff for the given reference.
 // If refName is empty, it will generate a diff of staged changes for the working directory.
 func generateDiff(w io.Writer, dir string, refName string, amend bool) error {