diff --git a/src/langserver/debugger/mod.rs b/src/langserver/debugger/mod.rs
new file mode 100644
index 00000000..b2c8d664
--- /dev/null
+++ b/src/langserver/debugger/mod.rs
@@ -0,0 +1,49 @@
+//! Debug adapter protocol implementation for DreamSeeker.
+//!
+//! * https://microsoft.github.io/debug-adapter-protocol/
+
+mod types;
+
+use std::error::Error;
+use io;
+use self::types::*;
+
+pub fn debugger_main<I: Iterator<Item=String>>(mut args: I) {
+    let mut dreamseeker_exe = None;
+
+    while let Some(arg) = args.next() {
+        if arg == "--dreamseeker-exe" {
+            dreamseeker_exe = Some(args.next().expect("must specify a value for --dreamseeker-exe"));
+        } else {
+            panic!("unknown argument {:?}", arg);
+        }
+    }
+
+    let mut debugger = Debugger {
+        dreamseeker_exe: dreamseeker_exe.expect("must provide argument `--dreamseeker-exe path/to/dreamseeker.exe`"),
+    };
+    io::run_forever(|message| debugger.handle_input(message));
+}
+
+struct Debugger {
+    dreamseeker_exe: String,
+}
+
+impl Debugger {
+    fn handle_input(&mut self, message: &str) {
+        // TODO: error handling
+        self.dispatch_input(message).expect("error in dispatch_input");
+    }
+
+    fn dispatch_input(&mut self, message: &str) -> Result<(), Box<dyn Error>> {
+        let protocol_message = serde_json::from_str::<ProtocolMessage>(message)?;
+        match protocol_message.type_.as_str() {
+            "request" => {
+                let request = serde_json::from_str::<Request>(message)?;
+                eprintln!("{:?}", request);
+            }
+            other => return Err(format!("unknown `type` field {:?}", other).into())
+        }
+        Ok(())
+    }
+}
diff --git a/src/langserver/debugger/types.rs b/src/langserver/debugger/types.rs
new file mode 100644
index 00000000..41d13930
--- /dev/null
+++ b/src/langserver/debugger/types.rs
@@ -0,0 +1,133 @@
+//! Serde types for the Debug Adapter Protocol.
+//!
+//! * https://microsoft.github.io/debug-adapter-protocol/specification
+
+use std::collections::HashMap;
+use serde_json::Value;
+
+// ----------------------------------------------------------------------------
+// Base Protocol
+
+/// Base class of requests, responses, and events.
+#[derive(Serialize, Deserialize, Debug)]
+pub struct ProtocolMessage {
+    /// Sequence number (also known as message ID). For protocol messages of type 'request' this ID can be used to cancel the request.
+    pub seq: i64,
+    #[serde(rename = "type")]
+    /// Message type.
+    /// Values: 'request', 'response', 'event', etc.
+    pub type_: String,
+}
+
+/// A client or debug adapter initiated request.
+#[derive(Serialize, Deserialize, Debug)]
+pub struct Request {
+    #[serde(flatten)]
+    pub protocol_message: ProtocolMessage,
+    /// The command to execute.
+    pub command: String,
+    /// Object containing arguments for the command.
+    pub arguments: Option<Value>,
+}
+
+/// A debug adapter initiated event.
+#[derive(Serialize, Deserialize, Debug)]
+pub struct Event {
+    #[serde(flatten)]
+    pub protocol_message: ProtocolMessage,
+    /// Type of event.
+    pub event: String,
+    /// Event-specific information.
+    pub body: Option<Value>,
+}
+
+/// Response for a request.
+#[derive(Serialize, Deserialize, Debug)]
+pub struct Response {
+    #[serde(flatten)]
+    pub protocol_message: ProtocolMessage,
+
+    /**
+     * Sequence number of the corresponding request.
+     */
+    pub request_seq: i64,
+
+    /**
+     * Outcome of the request.
+     * If true, the request was successful and the 'body' attribute may contain the result of the request.
+     * If the value is false, the attribute 'message' contains the error in short form and the 'body' may contain additional information (see 'ErrorResponse.body.error').
+     */
+    pub success: bool,
+
+    /**
+     * The command requested.
+     */
+    pub command: String,
+
+    /**
+     * Contains the raw error in short form if 'success' is false.
+     * This raw error might be interpreted by the frontend and is not shown in the UI.
+     * Some predefined values exist.
+     * Values:
+     * 'cancelled': request was cancelled.
+     * etc.
+     */
+    pub message: Option<String>,
+
+    /**
+     * Contains request result if success is true and optional error details if success is false.
+     */
+    pub body: Option<Value>,
+}
+
+/// On error (whenever ‘success’ is false), the body can provide more details.
+#[derive(Serialize, Deserialize, Debug)]
+pub struct ErrorResponseBody {
+    /// An optional, structured error message.
+    pub error: Option<Message>,
+}
+
+// ----------------------------------------------------------------------------
+// Types
+
+#[derive(Serialize, Deserialize, Debug)]
+pub struct Message {
+    /**
+     * Unique identifier for the message.
+     */
+    pub id: i64,
+
+    /**
+     * A format string for the message. Embedded variables have the form '{name}'.
+     * If variable name starts with an underscore character, the variable does not contain user data (PII) and can be safely used for telemetry purposes.
+     */
+    pub format: String,
+
+    /**
+     * An object used as a dictionary for looking up the variables in the format string.
+     */
+    pub variables: Option<HashMap<String, String>>,
+
+    /**
+     * If true send to telemetry.
+     */
+    #[serde(rename = "sendTelemetry")]
+    pub send_telemetry: Option<bool>,
+
+    /**
+     * If true show user.
+     */
+    #[serde(rename = "showUser")]
+    pub show_user: Option<bool>,
+
+    /**
+     * An optional url where additional information about this message can be found.
+     */
+    pub url: Option<String>,
+
+    /**
+     * An optional label that is presented to the user as the UI for opening the url.
+     */
+    #[serde(rename = "urlLabel")]
+    pub url_label: Option<String>,
+}
diff --git a/src/langserver/main.rs b/src/langserver/main.rs
index bc8a75ca..9082d359 100644
--- a/src/langserver/main.rs
+++ b/src/langserver/main.rs
@@ -27,6 +27,8 @@ mod find_references;
 mod extras;
 mod completion;
 
+mod debugger;
+
 use std::path::PathBuf;
 use std::collections::{HashMap, HashSet, VecDeque};
 use std::collections::hash_map::Entry;
@@ -62,6 +64,16 @@ fn main() {
         Err(e) => eprintln!("dir check failure: {}", e),
     }
 
+    let mut args = std::env::args();
+    let _ = args.next();  // skip executable name
+    if let Some(arg) = args.next() {
+        if arg == "--debugger" {
+            return debugger::debugger_main(args);
+        } else {
+            panic!("unknown argument {:?}", arg);
+        }
+    }
+
     let context = dm::Context::default();
     let mut engine = Engine::new(&context);
     io::run_forever(|message| engine.handle_input(message));