diff --git a/src/main/java/ru/itmo/ctlab/hict/hict_server/MainVerticle.java b/src/main/java/ru/itmo/ctlab/hict/hict_server/MainVerticle.java
index f4125ec..c6316f4 100644
--- a/src/main/java/ru/itmo/ctlab/hict/hict_server/MainVerticle.java
+++ b/src/main/java/ru/itmo/ctlab/hict/hict_server/MainVerticle.java
@@ -34,6 +34,7 @@
 import io.vertx.core.Promise;
 import io.vertx.core.Vertx;
 import io.vertx.core.http.HttpServerOptions;
+import io.vertx.core.json.Json;
 import io.vertx.core.json.JsonArray;
 import io.vertx.core.json.JsonObject;
 import io.vertx.core.logging.SLF4JLogDelegateFactory;
@@ -61,6 +62,7 @@
 import java.nio.file.Path;
 import java.util.ArrayList;
 import java.util.List;
+import java.util.Map;
 import java.util.concurrent.BrokenBarrierException;
 import java.util.concurrent.CyclicBarrier;
 
@@ -187,8 +189,12 @@ public void start(final Promise<Void> startPromise) throws Exception {
 
     router.route().failureHandler(ctx -> {
       log.error("An exception was caught at router top-level", ctx.failure());
-      ctx.response().end(
-          ctx.failure().getMessage());
+      final var message = ctx.failure() != null && ctx.failure().getMessage() != null
+        ? ctx.failure().getMessage()
+        : "Request failed";
+      ctx.response()
+        .putHeader("content-type", "application/json")
+        .end(Json.encode(Map.of("error", message)));
     });
 
     log.info("Configuring router");
diff --git a/src/main/java/ru/itmo/ctlab/hict/hict_server/handlers/fileop/FileOpHandlersHolder.java b/src/main/java/ru/itmo/ctlab/hict/hict_server/handlers/fileop/FileOpHandlersHolder.java
index eb84614..517706f 100644
--- a/src/main/java/ru/itmo/ctlab/hict/hict_server/handlers/fileop/FileOpHandlersHolder.java
+++ b/src/main/java/ru/itmo/ctlab/hict/hict_server/handlers/fileop/FileOpHandlersHolder.java
@@ -94,7 +94,9 @@ public void addHandlersToRouter(final @NotNull Router router) {
 
       map.put("TileStatisticHolder", TileStatisticHolder.newDefaultStatisticHolder(chunkedFile.getResolutions().length));
 
-      ctx.response().end(Json.encode(generateOpenFileResponse(chunkedFile)));
+      ctx.response()
+        .putHeader("content-type", "application/json")
+        .end(Json.encode(generateOpenFileResponse(chunkedFile)));
     });
 
     router.post("/attach").blockingHandler(ctx -> {
diff --git a/src/main/java/ru/itmo/ctlab/hict/hict_server/handlers/info/InfoHandlersHolder.java b/src/main/java/ru/itmo/ctlab/hict/hict_server/handlers/info/InfoHandlersHolder.java
index 7b7c7f2..4e2b504 100644
--- a/src/main/java/ru/itmo/ctlab/hict/hict_server/handlers/info/InfoHandlersHolder.java
+++ b/src/main/java/ru/itmo/ctlab/hict/hict_server/handlers/info/InfoHandlersHolder.java
@@ -26,10 +26,13 @@ public void addHandlersToRouter(final @NotNull Router router) {
     router.get("/version").handler(ctx -> {
       final var version = readVersion();
       final var webuiVersion = readWebUiVersion();
-      ctx.response().setStatusCode(200).end(Json.encode(Map.of(
-        "version", version,
-        "webuiVersion", webuiVersion
-      )));
+      ctx.response()
+        .putHeader("content-type", "application/json")
+        .setStatusCode(200)
+        .end(Json.encode(Map.of(
+          "version", version,
+          "webuiVersion", webuiVersion
+        )));
     });
   }
 
diff --git a/src/main/java/ru/itmo/ctlab/hict/hict_server/handlers/tiles/TileHandlersHolder.java b/src/main/java/ru/itmo/ctlab/hict/hict_server/handlers/tiles/TileHandlersHolder.java
index fa9d343..d3b9511 100644
--- a/src/main/java/ru/itmo/ctlab/hict/hict_server/handlers/tiles/TileHandlersHolder.java
+++ b/src/main/java/ru/itmo/ctlab/hict/hict_server/handlers/tiles/TileHandlersHolder.java
@@ -83,7 +83,10 @@ public void addHandlersToRouter(final @NotNull Router router) {
         return;
       }
       final var options = visualizationOptionsWrapper.getSimpleVisualizationOptions();
-      ctx.response().setStatusCode(200).end(Json.encode(VisualizationOptionsDTO.fromEntity(options, chunkedFile)));
+      ctx.response()
+        .putHeader("content-type", "application/json")
+        .setStatusCode(200)
+        .end(Json.encode(VisualizationOptionsDTO.fromEntity(options, chunkedFile)));
     });
 
     router.post("/get_visualization_options").blockingHandler(ctx -> {
@@ -102,7 +105,10 @@ public void addHandlersToRouter(final @NotNull Router router) {
         return;
       }
       final var options = visualizationOptionsWrapper.getSimpleVisualizationOptions();
-      ctx.response().setStatusCode(200).end(Json.encode(VisualizationOptionsDTO.fromEntity(options, chunkedFile)));
+      ctx.response()
+        .putHeader("content-type", "application/json")
+        .setStatusCode(200)
+        .end(Json.encode(VisualizationOptionsDTO.fromEntity(options, chunkedFile)));
     });
 
     router.post("/tiles/reload").blockingHandler(ctx -> {