diff --git a/src/aimedb/decoder.ts b/src/aimedb/decoder.ts
index fbe821d..16af3af 100644
--- a/src/aimedb/decoder.ts
+++ b/src/aimedb/decoder.ts
@@ -121,7 +121,7 @@ export class Decoder extends Transform {
 
     const obj = reader(msg);
 
-    debug(`Decode ${JSON.stringify(obj)}`);
+    debug("Decode %j", obj);
 
     return callback(null, obj);
   }
diff --git a/src/aimedb/encoder.ts b/src/aimedb/encoder.ts
index 4436a44..3c5929c 100644
--- a/src/aimedb/encoder.ts
+++ b/src/aimedb/encoder.ts
@@ -30,7 +30,7 @@ export class Encoder extends Transform {
   }
 
   _transform(msg: AimeResponse, encoding, callback) {
-    debug(`Encode ${JSON.stringify(msg)}`);
+    debug("Encode %j", msg);
 
     let buf: Buffer;
 
@@ -108,7 +108,9 @@ export class Encoder extends Transform {
         return callback(new Error("Unimplemented response type"));
     }
 
-    debug(`Send ${buf.toString("hex")}`);
+    if (debug.enabled) {
+      debug("Send %s", buf.toString("hex"));
+    }
 
     return callback(null, buf);
   }
diff --git a/src/aimedb/frame.ts b/src/aimedb/frame.ts
index 1037248..139efe0 100644
--- a/src/aimedb/frame.ts
+++ b/src/aimedb/frame.ts
@@ -36,7 +36,9 @@ export class Deframer extends Transform {
 
     const frame = this.state.slice(0, len);
 
-    debug(`Recv ${frame.toString("hex")}`);
+    if (debug.enabled) {
+      debug("Recv %s", frame.toString("hex"));
+    }
 
     this.state = this.state.slice(len);
 
diff --git a/src/aimedb/handler.ts b/src/aimedb/handler.ts
index c93fbcc..ed3e24e 100644
--- a/src/aimedb/handler.ts
+++ b/src/aimedb/handler.ts
@@ -53,7 +53,7 @@ async function lookup(
   req: Req.LookupRequest,
   now: Date
 ): Promise<Res.LookupResponse> {
-  debug(`Mifare lookup v1: luid=${req.luid}`);
+  debug("Mifare lookup: luid=%s", req.luid);
 
   return {
     type: req.type,
@@ -68,7 +68,7 @@ async function lookup2(
   req: Req.LookupRequest2,
   now: Date
 ): Promise<Res.LookupResponse2> {
-  debug(`Mifare lookup v2: luid=${req.luid}`);
+  debug("FeliCa lookup: luid=%s", req.luid);
 
   return {
     type: req.type,
@@ -83,7 +83,7 @@ async function register(
   req: Req.RegisterRequest,
   now: Date
 ): Promise<Res.RegisterResponse> {
-  debug(`User register: luid=${req.luid}`);
+  debug("User register: luid=%s", req.luid);
 
   return {
     type: req.type,
diff --git a/src/aimedb/index.ts b/src/aimedb/index.ts
index 5538854..c1f26e5 100644
--- a/src/aimedb/index.ts
+++ b/src/aimedb/index.ts
@@ -28,7 +28,9 @@ export default function aimedb(db: DataSource) {
 
         output.write(res);
       } catch (e) {
-        debug(`Connection error:\n${e.toString()}\n`);
+        if (debug.enabled) {
+          debug("Connection error: %s", e.stack);
+        }
 
         break;
       }
diff --git a/src/allnet.ts b/src/allnet.ts
index bce3255..79b5926 100644
--- a/src/allnet.ts
+++ b/src/allnet.ts
@@ -59,8 +59,8 @@ app.use("/sys/servlet/PowerOn", async function(req, res, next) {
   return next();
 });
 
-app.post("/sys/servlet/PowerOn", function(req, resp) {
-  debug(`Startup Request: ${JSON.stringify(req.body)}`);
+app.post("/sys/servlet/PowerOn", function(req, res) {
+  debug("Startup request: %j", req.body);
 
   // Cut milliseconds out of ISO timestamp
 
@@ -91,9 +91,9 @@ app.post("/sys/servlet/PowerOn", function(req, resp) {
     token: req.body.token,
   };
 
-  debug(`Startup response: ${JSON.stringify(resParams)}`);
+  debug("Startup response: %j", resParams);
 
-  resp.send(resParams);
+  res.send(resParams);
 });
 
 export default app;
diff --git a/src/billing.ts b/src/billing.ts
index 57460a1..c9cae75 100644
--- a/src/billing.ts
+++ b/src/billing.ts
@@ -62,7 +62,7 @@ app.use(async function(req, res, next) {
 });
 
 app.post("/request/", function(req, res) {
-  debug(`Billing request: ${JSON.stringify(req.body)}`);
+  debug("Billing request: %j", req.body);
 
   const first = req.body[0];
 
@@ -135,7 +135,7 @@ app.post("/request/", function(req, res) {
     playhistory: "000000/0:000000/0:000000/0",
   });
 
-  debug(`Billing response: ${JSON.stringify(resItems)}`);
+  debug("Billing response: %j", resItems);
 
   res.set("content-type", "text/plain");
   res.send(resItems);
diff --git a/src/checkdb.ts b/src/checkdb.ts
index 0e0f3cf..d772748 100644
--- a/src/checkdb.ts
+++ b/src/checkdb.ts
@@ -42,7 +42,7 @@ async function initdb(txn: Transaction): Promise<void> {
   debug("Initializing database");
 
   for (const script of scripts) {
-    debug(`Executing ${script}`);
+    debug("Executing %s", script);
 
     const scriptPath = resolve(initPath, script);
     const scriptSql = readFileSync(scriptPath, "utf-8");
@@ -56,7 +56,7 @@ async function initdb(txn: Transaction): Promise<void> {
 
   await txn.modify(metaInsert);
 
-  debug(`Initialized new database to schema version ${schemaver}`);
+  debug("Initialized new database to schema version %s", schemaver);
 }
 
 async function migratedb(
@@ -72,7 +72,7 @@ async function migratedb(
     const captures = filename.match(migrateRx);
 
     if (captures === null) {
-      debug(`Warning: Unexpected file ${filename} in SQL migrations dir`);
+      debug("Warning: Unexpected file %s in SQL migrations dir", filename);
 
       continue;
     }
@@ -83,7 +83,7 @@ async function migratedb(
       continue;
     }
 
-    debug(`Executing database upgrade: ${filename}`);
+    debug("Executing database upgrade: %s", filename);
 
     const scriptPath = resolve(migratePath, filename);
     const scriptSql = readFileSync(scriptPath, "utf-8");
@@ -126,7 +126,7 @@ export default async function checkdb(db: DataSource): Promise<void> {
   const newver = await db.transaction(txn => migratedb(txn, schemaver));
 
   if (newver !== undefined) {
-    debug(`Upgraded database to version ${newver}`);
+    debug("Upgraded database to version %s", newver);
 
     await db.vacuum();
 
diff --git a/src/chunithm/index.ts b/src/chunithm/index.ts
index 5579f56..e233294 100644
--- a/src/chunithm/index.ts
+++ b/src/chunithm/index.ts
@@ -42,13 +42,13 @@ app.use(express.json());
 // Trace requests and responses
 
 app.use(function(req, resp, next) {
-  debug(`\n--- Chunithm ${req.url} ---\n`);
-  debug(`Request: ${JSON.stringify(req.body)}\n`);
+  debug("\n--- Chunithm %s ---\n", req.url);
+  debug("Request: %j", req.body);
 
   const prevJson = resp.json;
 
   resp.json = function(obj) {
-    debug(`Response: ${JSON.stringify(obj)}`);
+    debug("Response: %j", obj);
 
     resp.json = prevJson;
     resp.json.apply(this, arguments);
diff --git a/src/diva/index.ts b/src/diva/index.ts
index b86f175..930073a 100644
--- a/src/diva/index.ts
+++ b/src/diva/index.ts
@@ -25,7 +25,7 @@ app.use(async function(req, res, next) {
   const send_ = res.send;
 
   res.send = function(kvps) {
-    debug(`Response: ${JSON.stringify(kvps)}\n`);
+    debug("Response: %j", kvps);
 
     const bits: string[] = [];
 
@@ -68,7 +68,7 @@ app.use(async function(req, res, next) {
     req.body = body;
 
     debug("\n--- Diva ---\n");
-    debug(`Request: ${JSON.stringify(req.body)}\n`);
+    debug("Request: %j", req.body);
 
     return next();
   } else if (req.is("multipart/form-data")) {
@@ -82,7 +82,7 @@ app.use(async function(req, res, next) {
       req.body = { ...files, ...fields };
 
       debug("\n--- Diva (Multipart) ---\n");
-      debug(`Request: ${JSON.stringify(req.body)}\n`);
+      debug("Request: %j", req.body);
 
       return next();
     });
diff --git a/src/idz/decoder/index.ts b/src/idz/decoder/index.ts
index 126cb63..ec8574f 100644
--- a/src/idz/decoder/index.ts
+++ b/src/idz/decoder/index.ts
@@ -184,8 +184,10 @@ export class Decoder extends Transform {
     const reqBuf = this.state.slice(0, 0x30 + msgLen);
     const payloadBuf = reqBuf.slice(0x30);
 
-    debug(`Raw: ${reqBuf.toString("hex")}`);
-    debug(`Header: ${JSON.stringify(header)}`);
+    if (debug.enabled) {
+      debug("Raw: %s", reqBuf.toString("hex"));
+      debug("Header: %j", header);
+    }
 
     const reader = readerFns.get(msgCode);
 
@@ -197,7 +199,7 @@ export class Decoder extends Transform {
 
     const payload = reader(payloadBuf);
 
-    debug(`Payload: ${JSON.stringify(payload)}`);
+    debug("Payload: %j", payload);
 
     return callback(null, payload);
   }
diff --git a/src/idz/encoder/index.ts b/src/idz/encoder/index.ts
index e35af94..c890069 100644
--- a/src/idz/encoder/index.ts
+++ b/src/idz/encoder/index.ts
@@ -150,11 +150,13 @@ export class Encoder extends Transform {
   }
 
   _transform(res: Response, encoding, callback) {
-    debug(`Object: ${JSON.stringify(res)}`);
+    debug("Object: %j", res);
 
     const buf = encode(res);
 
-    debug(`Encoded: ${buf.toString("hex")}`);
+    if (debug.enabled) {
+      debug("Encoded: %s", buf.toString("hex"));
+    }
 
     if (buf.readInt16LE(0) === 0) {
       throw new Error("Missing message type code");
diff --git a/src/idz/index.ts b/src/idz/index.ts
index 9439f93..7d3d5fd 100644
--- a/src/idz/index.ts
+++ b/src/idz/index.ts
@@ -18,7 +18,9 @@ export default function idz(db: DataSource) {
         output.write(await db.transaction(txn => dispatch(txn, req)));
       }
     } catch (e) {
-      debug(`Error:\n${e.toString()}`);
+      if (debug.enabled) {
+        debug("Error: %s", e.stack);
+      }
     }
 
     debug("Connection closed");
diff --git a/src/idz/ping.ts b/src/idz/ping.ts
index 66d8172..df6f3dc 100644
--- a/src/idz/ping.ts
+++ b/src/idz/ping.ts
@@ -8,7 +8,7 @@ export default function createPing(port: number, host: string) {
 
   socket.bind(port, host);
   socket.on("message", (msg, rinfo) => {
-    debug(`Ping from ${rinfo.address}:${rinfo.port}`);
+    debug("Ping from %s:%s", rinfo.address, rinfo.port);
     socket.send(msg, rinfo.port, rinfo.address);
   });
 }
diff --git a/src/switchboard.ts b/src/switchboard.ts
index 99c550c..e91abff 100644
--- a/src/switchboard.ts
+++ b/src/switchboard.ts
@@ -73,8 +73,8 @@ export function startupUri(model: string): string {
 // Diagnostic dump
 //
 
-debug(`HOST_EXT: ${HOST_EXT} (Service host name sent to clients)`);
-debug(`HOST_INT: ${HOST_INT} (Bind address)`);
+debug("HOST_EXT: %s (Service host name sent to clients)", HOST_EXT);
+debug("HOST_INT: %s (Bind address)", HOST_INT);
 
 if (cfgHostExt === undefined || cfgHostInt === undefined) {
   debug(