diff --git a/Cli/App.swift b/Cli/App.swift
index fdf5278..fd5cce3 100644
--- a/Cli/App.swift
+++ b/Cli/App.swift
@@ -1,11 +1,32 @@
+// Marker CLI entry point.
+// (c) Kyrylo Khlopko
+
+#if canImport(Darwin)
+    import Darwin
+#else
+    import Glibc
+#endif
+
+import ArgumentParser
+
 import DotMd
 
 @main
-struct App {
-    static func main() throws {
-        //let path = "Examples/markdown/bench.md"
-        let path = "README.md"
-        let md = try Markdown(path: path)
+struct Cli: ParsableCommand {
+    @Argument
+    var inputFilePath: String
+    
+    mutating func run() throws {
+        let file = fopen(inputFilePath, "r")
+        defer { fclose(file) }
+        var contents = ""
+        var buf = Array(repeating: CChar(0), count: 1024)
+        while fgets(&buf, Int32(1024), file) != nil {
+            if let chunk = String(validatingUTF8: buf) {
+                contents += chunk
+            }
+        }
+        let md = try Markdown(contents: contents)
         print(md)
     }
 }
diff --git a/Markdown/Lexer.swift b/Markdown/Lexer.swift
new file mode 100644
index 0000000..01236a3
--- /dev/null
+++ b/Markdown/Lexer.swift
@@ -0,0 +1,64 @@
+//  Markdown lexer implementation
+//  (c) Kyrylo Khlopko
+
+internal enum MarkdownToken {
+    case newline
+    case line(String)
+    case header(HeaderLevel)
+}
+
+internal struct Lexer {
+    private let contents: [Character]
+    private var lastPos = 0
+
+    init(contents: String) {
+        self.contents = Array(contents)
+    }
+
+    init(contents: [Character]) {
+        self.contents = contents
+    }
+
+    mutating func nextTok() -> MarkdownToken? {
+        guard lastPos < contents.count else {
+            return nil
+        }
+        let start = lastPos
+        switch contents[lastPos] {
+        case "\n":
+            lastPos += 1
+            return .newline
+        case "#":
+            return header(start: start)
+        default: 
+            return line(start: start)
+        }
+    }
+
+    private mutating func header(start: Int) -> MarkdownToken {
+        var level = 0
+        while lastPos < contents.count && contents[lastPos] == "#" {
+            level += 1
+            lastPos += 1
+        }
+        guard 
+            let headerLevel = HeaderLevel(rawValue: level),
+            contents[lastPos] == " " 
+        else {
+            return line(start: start)
+        }
+        lastPos += 1
+        return .header(headerLevel)
+    }
+
+    private mutating func line(start: Int) -> MarkdownToken {
+        guard start < contents.count else {
+            return .line(String(contents[start...]))
+        }
+        while lastPos < contents.count && contents[lastPos] != "\n" {
+            lastPos += 1
+        }
+        return .line(String(contents[start..<lastPos]))
+    }
+}
+
diff --git a/Markdown/Markdown.swift b/Markdown/Markdown.swift
index 42ec6b1..9931ea7 100644
--- a/Markdown/Markdown.swift
+++ b/Markdown/Markdown.swift
@@ -1,22 +1,18 @@
-// Markdown.swift
-
-import Foundation 
+// Parsed markdown representation
+//  (c) Kyrylo Khlopko
 
 public struct Markdown {
     public let blocks: [Block]
 
-    public init(path: String) throws {
-        let contents = try String(contentsOfFile: path)
-        var parser = MarkdownParser(contents: Array(contents))
+    public init(contents: String) throws {
+        var parser = Parser(contents: Array(contents))
         self.blocks = parser.parse()
     }
 }
 
 extension Markdown: CustomStringConvertible {
     public var description: String {
-        blocks.map { block in
-            block.description
-        }.joined(separator: "\n")
+        blocks.map(\.description).joined(separator: "\n")
     }
 }
 
@@ -54,131 +50,3 @@ public enum TextStyle: Equatable {
     case regular
 }
 
-struct MarkdownParser {
-    private var lexer: MarkdownLexer
-
-    init(contents: String) {
-        lexer = MarkdownLexer(contents: contents)
-    }
-
-    init(contents: [Character]) {
-        lexer = MarkdownLexer(contents: contents)
-    }
-
-    private var blocks: [Block] = []
-    private var paragraphValue: String = ""
-    private var readingParagraph = false
-
-    mutating func parse() -> [Block] {
-        setup()
-        while let tok = lexer.nextTok() {
-            switch tok {
-            case .newline:
-                checkParagraph()
-            case let .line(value):
-                parseLine(value: value)
-            case let .header(level):
-                checkParagraph()
-                parseHeader(level: level)
-            }
-        }
-        checkParagraph()
-        return blocks
-    }
-
-    private mutating func setup() {
-        blocks = []
-        paragraphValue = ""
-        readingParagraph = false
-    }
-
-    private mutating func parseLine(value: String) {
-        if readingParagraph {
-            paragraphValue += "\n"
-            paragraphValue += value
-        } else {
-            readingParagraph = true
-            paragraphValue = value
-        }
-        _ = lexer.nextTok() // consume newline
-    }
-
-    private mutating func parseHeader(level: HeaderLevel) {
-        let nextTok = lexer.nextTok()
-        var headerValue: Block = .p([.text("", .regular)])
-        if case let .line(value) = nextTok {
-            headerValue = .p([.text(value, .regular)])
-        }
-        blocks.append(.h(level, headerValue))
-        _ = lexer.nextTok() // consume newline
-    }
-
-    private mutating func checkParagraph() {
-        if readingParagraph {
-            blocks.append(.p([.text(paragraphValue, .regular)]))
-            readingParagraph = false
-        }
-    }
-}
-
-enum MarkdownToken {
-    case newline
-    case line(String)
-    case header(HeaderLevel)
-}
-
-struct MarkdownLexer {
-    private let contents: [Character]
-    private var lastPos = 0
-
-    init(contents: String) {
-        self.contents = Array(contents)
-    }
-
-    init(contents: [Character]) {
-        self.contents = contents
-    }
-
-    mutating func nextTok() -> MarkdownToken? {
-        guard lastPos < contents.count else {
-            return nil
-        }
-        let start = lastPos
-        switch contents[lastPos] {
-        case "\n":
-            lastPos += 1
-            return .newline
-        case "#":
-            return header(start: start)
-        default: 
-            return line(start: start)
-        }
-    }
-
-    private mutating func header(start: Int) -> MarkdownToken {
-        var level = 0
-        while lastPos < contents.count && contents[lastPos] == "#" {
-            level += 1
-            lastPos += 1
-        }
-        guard 
-            let headerLevel = HeaderLevel(rawValue: level),
-            contents[lastPos] == " " 
-        else {
-            return line(start: start)
-        }
-        lastPos += 1
-        return .header(headerLevel)
-    }
-
-    private mutating func line(start: Int) -> MarkdownToken {
-        guard start < contents.count else {
-            return .line(String(contents[start...]))
-        }
-        while lastPos < contents.count && contents[lastPos] != "\n" {
-            lastPos += 1
-        }
-        return .line(String(contents[start..<lastPos]))
-    }
-}
-
diff --git a/Markdown/Parser.swift b/Markdown/Parser.swift
new file mode 100644
index 0000000..5b2dc93
--- /dev/null
+++ b/Markdown/Parser.swift
@@ -0,0 +1,69 @@
+//  Markdown parser implementation
+//  (c) Kyrylo Khlopko
+
+internal struct Parser {
+    private var lexer: Lexer
+
+    init(contents: String) {
+        lexer = Lexer(contents: contents)
+    }
+
+    init(contents: [Character]) {
+        lexer = Lexer(contents: contents)
+    }
+
+    private var blocks: [Block] = []
+    private var paragraphValue: String = ""
+    private var readingParagraph = false
+
+    mutating func parse() -> [Block] {
+        setup()
+        while let tok = lexer.nextTok() {
+            switch tok {
+            case .newline:
+                checkParagraph()
+            case let .line(value):
+                parseLine(value: value)
+            case let .header(level):
+                checkParagraph()
+                parseHeader(level: level)
+            }
+        }
+        checkParagraph()
+        return blocks
+    }
+
+    private mutating func setup() {
+        blocks = []
+        paragraphValue = ""
+        readingParagraph = false
+    }
+
+    private mutating func parseLine(value: String) {
+        if readingParagraph {
+            paragraphValue += "\n"
+            paragraphValue += value
+        } else {
+            readingParagraph = true
+            paragraphValue = value
+        }
+        _ = lexer.nextTok() // consume newline
+    }
+
+    private mutating func parseHeader(level: HeaderLevel) {
+        let nextTok = lexer.nextTok()
+        var headerValue: Block = .p([.text("", .regular)])
+        if case let .line(value) = nextTok {
+            headerValue = .p([.text(value, .regular)])
+        }
+        blocks.append(.h(level, headerValue))
+        _ = lexer.nextTok() // consume newline
+    }
+
+    private mutating func checkParagraph() {
+        if readingParagraph {
+            blocks.append(.p([.text(paragraphValue, .regular)]))
+            readingParagraph = false
+        }
+    }
+}
diff --git a/Package.resolved b/Package.resolved
index b7df665..a8b3698 100644
--- a/Package.resolved
+++ b/Package.resolved
@@ -1,6 +1,15 @@
 {
-  "originHash" : "ccfcb9545e17b683fc71f240b434fd9e699c7ad431a4508c9f6f5aef1185ef39",
+  "originHash" : "8d3c5bcf931d8172b0afa33fe2a5e54c7b37c0c93c050aa2b4f6a78e0b00dc1d",
   "pins" : [
+    {
+      "identity" : "swift-argument-parser",
+      "kind" : "remoteSourceControl",
+      "location" : "https://github.com/apple/swift-argument-parser.git",
+      "state" : {
+        "revision" : "46989693916f56d1186bd59ac15124caef896560",
+        "version" : "1.3.1"
+      }
+    },
     {
       "identity" : "swift-syntax",
       "kind" : "remoteSourceControl",
diff --git a/Package.swift b/Package.swift
index 7648ede..cac0c37 100644
--- a/Package.swift
+++ b/Package.swift
@@ -12,12 +12,14 @@ let package = Package(
     ],
     dependencies: [
         .package(url: "https://github.com/apple/swift-testing.git", branch: "main"),
+        .package(url: "https://github.com/apple/swift-argument-parser.git", from: "1.3.0"),
     ],
     targets: [
         .executableTarget(
             name: "Marker",
             dependencies: [
                 .target(name: "DotMd"),
+                .product(name: "ArgumentParser", package: "swift-argument-parser"),
             ],
             path: "Cli"
         ),
diff --git a/README.md b/README.md
index 7dc4a5a..d2c3467 100644
--- a/README.md
+++ b/README.md
@@ -1,7 +1,6 @@
-# Marker
 [![tests](https://github.com/khlopko/marker/actions/workflows/test.yml/badge.svg?branch=main&event=push)](https://github.com/khlopko/marker/actions/workflows/test.yml)
-
-A static web site generator, written in Swift, with a focus on simplicity and ease of use.
+# Marker
+❤️ A static web site generator, written in Swift, with a focus on simplicity and ease of use.
 
 ## (Upcoming) Features