diff --git a/Sources/imsg/CommandRouter.swift b/Sources/imsg/CommandRouter.swift
index 7d819f9..d198e6f 100644
--- a/Sources/imsg/CommandRouter.swift
+++ b/Sources/imsg/CommandRouter.swift
@@ -33,7 +33,7 @@ struct CommandRouter {
   func run(argv: [String]) async -> Int32 {
     let argv = normalizeArguments(argv)
     if argv.contains("--version") || argv.contains("-V") {
-      Swift.print(version)
+      StdoutWriter.writeLine(version)
       return 0
     }
     if argv.count <= 1 || argv.contains("--help") || argv.contains("-h") {
@@ -46,7 +46,7 @@ struct CommandRouter {
       guard let commandName = invocation.path.last,
         let spec = specs.first(where: { $0.name == commandName })
       else {
-        Swift.print("Unknown command")
+        StdoutWriter.writeLine("Unknown command")
         HelpPrinter.printRoot(version: version, rootName: rootName, commands: specs)
         return 1
       }
@@ -55,17 +55,17 @@ struct CommandRouter {
         try await spec.run(invocation.parsedValues, runtime)
         return 0
       } catch {
-        Swift.print(error)
+        StdoutWriter.writeLine(String(describing: error))
         return 1
       }
     } catch let error as CommanderProgramError {
-      Swift.print(error.description)
+      StdoutWriter.writeLine(error.description)
       if case .missingSubcommand = error {
         HelpPrinter.printRoot(version: version, rootName: rootName, commands: specs)
       }
       return 1
     } catch {
-      Swift.print(error)
+      StdoutWriter.writeLine(String(describing: error))
       return 1
     }
   }
diff --git a/Sources/imsg/Commands/ChatsCommand.swift b/Sources/imsg/Commands/ChatsCommand.swift
index dae76dc..baa447b 100644
--- a/Sources/imsg/Commands/ChatsCommand.swift
+++ b/Sources/imsg/Commands/ChatsCommand.swift
@@ -26,14 +26,14 @@ enum ChatsCommand {
 
     if runtime.jsonOutput {
       for chat in chats {
-        try JSONLines.print(ChatPayload(chat: chat))
+        try StdoutWriter.writeJSONLine(ChatPayload(chat: chat))
       }
       return
     }
 
     for chat in chats {
       let last = CLIISO8601.format(chat.lastMessageAt)
-      Swift.print("[\(chat.id)] \(chat.name) (\(chat.identifier)) last=\(last)")
+      StdoutWriter.writeLine("[\(chat.id)] \(chat.name) (\(chat.identifier)) last=\(last)")
     }
   }
 }
diff --git a/Sources/imsg/Commands/HistoryCommand.swift b/Sources/imsg/Commands/HistoryCommand.swift
index 2d6c057..407eb79 100644
--- a/Sources/imsg/Commands/HistoryCommand.swift
+++ b/Sources/imsg/Commands/HistoryCommand.swift
@@ -57,7 +57,7 @@ enum HistoryCommand {
           attachments: attachments,
           reactions: reactions
         )
-        try JSONLines.print(payload)
+        try StdoutWriter.writeJSONLine(payload)
       }
       return
     }
@@ -65,18 +65,18 @@ enum HistoryCommand {
     for message in filtered {
       let direction = message.isFromMe ? "sent" : "recv"
       let timestamp = CLIISO8601.format(message.date)
-      Swift.print("\(timestamp) [\(direction)] \(message.sender): \(message.text)")
+      StdoutWriter.writeLine("\(timestamp) [\(direction)] \(message.sender): \(message.text)")
       if message.attachmentsCount > 0 {
         if showAttachments {
           let metas = try store.attachments(for: message.rowID)
           for meta in metas {
             let name = displayName(for: meta)
-            Swift.print(
+            StdoutWriter.writeLine(
               "  attachment: name=\(name) mime=\(meta.mimeType) missing=\(meta.missing) path=\(meta.originalPath)"
             )
           }
         } else {
-          Swift.print(
+          StdoutWriter.writeLine(
             "  (\(message.attachmentsCount) attachment\(pluralSuffix(for: message.attachmentsCount)))"
           )
         }
diff --git a/Sources/imsg/Commands/SendCommand.swift b/Sources/imsg/Commands/SendCommand.swift
index 3c9a707..3fdad4f 100644
--- a/Sources/imsg/Commands/SendCommand.swift
+++ b/Sources/imsg/Commands/SendCommand.swift
@@ -91,9 +91,9 @@ enum SendCommand {
       ))
 
     if runtime.jsonOutput {
-      try JSONLines.print(["status": "sent"])
+      try StdoutWriter.writeJSONLine(["status": "sent"])
     } else {
-      Swift.print("sent")
+      StdoutWriter.writeLine("sent")
     }
   }
 }
diff --git a/Sources/imsg/Commands/WatchCommand.swift b/Sources/imsg/Commands/WatchCommand.swift
index abc86a7..36b2797 100644
--- a/Sources/imsg/Commands/WatchCommand.swift
+++ b/Sources/imsg/Commands/WatchCommand.swift
@@ -1,5 +1,4 @@
 import Commander
-import Darwin
 import Foundation
 import IMsgCore
 
@@ -90,29 +89,27 @@ enum WatchCommand {
           attachments: attachments,
           reactions: reactions
         )
-        try JSONLines.print(payload)
-        fflush(stdout)
+        try StdoutWriter.writeJSONLine(payload)
         continue
       }
       let direction = message.isFromMe ? "sent" : "recv"
       let timestamp = CLIISO8601.format(message.date)
-      Swift.print("\(timestamp) [\(direction)] \(message.sender): \(message.text)")
+      StdoutWriter.writeLine("\(timestamp) [\(direction)] \(message.sender): \(message.text)")
       if message.attachmentsCount > 0 {
         if showAttachments {
           let metas = try store.attachments(for: message.rowID)
           for meta in metas {
             let name = displayName(for: meta)
-            Swift.print(
+            StdoutWriter.writeLine(
               "  attachment: name=\(name) mime=\(meta.mimeType) missing=\(meta.missing) path=\(meta.originalPath)"
             )
           }
         } else {
-          Swift.print(
+          StdoutWriter.writeLine(
             "  (\(message.attachmentsCount) attachment\(pluralSuffix(for: message.attachmentsCount)))"
           )
         }
       }
-      fflush(stdout)
     }
   }
 }
diff --git a/Sources/imsg/HelpPrinter.swift b/Sources/imsg/HelpPrinter.swift
index 14a9209..a0bba67 100644
--- a/Sources/imsg/HelpPrinter.swift
+++ b/Sources/imsg/HelpPrinter.swift
@@ -4,13 +4,13 @@ import Foundation
 struct HelpPrinter {
   static func printRoot(version: String, rootName: String, commands: [CommandSpec]) {
     for line in renderRoot(version: version, rootName: rootName, commands: commands) {
-      Swift.print(line)
+      StdoutWriter.writeLine(line)
     }
   }
 
   static func printCommand(rootName: String, spec: CommandSpec) {
     for line in renderCommand(rootName: rootName, spec: spec) {
-      Swift.print(line)
+      StdoutWriter.writeLine(line)
     }
   }
 
diff --git a/Sources/imsg/JSONLines.swift b/Sources/imsg/JSONLines.swift
index a34e46f..893a4be 100644
--- a/Sources/imsg/JSONLines.swift
+++ b/Sources/imsg/JSONLines.swift
@@ -15,7 +15,7 @@ enum JSONLines {
   static func print<T: Encodable>(_ value: T) throws {
     let line = try encode(value)
     if !line.isEmpty {
-      Swift.print(line)
+      StdoutWriter.writeLine(line)
     }
   }
 }
diff --git a/Sources/imsg/RPCServer.swift b/Sources/imsg/RPCServer.swift
index 6109005..4f0a470 100644
--- a/Sources/imsg/RPCServer.swift
+++ b/Sources/imsg/RPCServer.swift
@@ -286,8 +286,6 @@ private func buildMessagePayload(
 }
 
 private final class RPCWriter: RPCOutput, @unchecked Sendable {
-  private let queue = DispatchQueue(label: "imsg.rpc.writer")
-
   func sendResponse(id: Any, result: Any) {
     send(["jsonrpc": "2.0", "id": id, "result": result])
   }
@@ -306,21 +304,15 @@ private final class RPCWriter: RPCOutput, @unchecked Sendable {
   }
 
   private func send(_ object: Any) {
-    queue.sync {
-      do {
-        let data = try JSONSerialization.data(withJSONObject: object, options: [])
-        if let output = String(data: data, encoding: .utf8) {
-          FileHandle.standardOutput.write(Data(output.utf8))
-          FileHandle.standardOutput.write(Data("\n".utf8))
-        }
-      } catch {
-        if let fallback =
-          "{\"jsonrpc\":\"2.0\",\"error\":{\"code\":-32603,\"message\":\"write failed\"}}\n"
-          .data(using: .utf8)
-        {
-          FileHandle.standardOutput.write(fallback)
-        }
+    do {
+      let data = try JSONSerialization.data(withJSONObject: object, options: [])
+      if let output = String(data: data, encoding: .utf8) {
+        StdoutWriter.writeLine(output)
       }
+    } catch {
+      StdoutWriter.writeLine(
+        "{\"jsonrpc\":\"2.0\",\"error\":{\"code\":-32603,\"message\":\"write failed\"}}"
+      )
     }
   }
 }
diff --git a/Sources/imsg/StdoutWriter.swift b/Sources/imsg/StdoutWriter.swift
new file mode 100644
index 0000000..acdebef
--- /dev/null
+++ b/Sources/imsg/StdoutWriter.swift
@@ -0,0 +1,24 @@
+import Dispatch
+import Foundation
+
+enum StdoutWriter {
+  private static let queue = DispatchQueue(label: "imsg.stdout.writer")
+
+  private static let jsonEncoder: JSONEncoder = {
+    let encoder = JSONEncoder()
+    encoder.outputFormatting = [.withoutEscapingSlashes]
+    return encoder
+  }()
+
+  static func writeLine(_ line: String) {
+    queue.sync {
+      FileHandle.standardOutput.write(Data((line + "\n").utf8))
+    }
+  }
+
+  static func writeJSONLine<T: Encodable>(_ value: T) throws {
+    let data = try jsonEncoder.encode(value)
+    guard let line = String(data: data, encoding: .utf8), !line.isEmpty else { return }
+    writeLine(line)
+  }
+}
diff --git a/Tests/imsgTests/CommandRouterTests.swift b/Tests/imsgTests/CommandRouterTests.swift
index f55f77b..82fefa0 100644
--- a/Tests/imsgTests/CommandRouterTests.swift
+++ b/Tests/imsgTests/CommandRouterTests.swift
@@ -4,25 +4,31 @@ import Testing
 @testable import imsg
 
 @Test
-func commandRouterPrintsVersionFromEnv() async throws {
+func commandRouterPrintsVersionFromEnv() async {
   setenv("IMSG_VERSION", "9.9.9-test", 1)
   defer { unsetenv("IMSG_VERSION") }
   let router = CommandRouter()
   #expect(router.version == "9.9.9-test")
-  let status = await router.run(argv: ["imsg", "--version"])
+  let (_, status) = await StdoutCapture.capture {
+    await router.run(argv: ["imsg", "--version"])
+  }
   #expect(status == 0)
 }
 
 @Test
 func commandRouterPrintsHelp() async {
   let router = CommandRouter()
-  let status = await router.run(argv: ["imsg", "--help"])
+  let (_, status) = await StdoutCapture.capture {
+    await router.run(argv: ["imsg", "--help"])
+  }
   #expect(status == 0)
 }
 
 @Test
 func commandRouterUnknownCommand() async {
   let router = CommandRouter()
-  let status = await router.run(argv: ["imsg", "nope"])
+  let (_, status) = await StdoutCapture.capture {
+    await router.run(argv: ["imsg", "nope"])
+  }
   #expect(status == 1)
 }
diff --git a/Tests/imsgTests/CommandTests.swift b/Tests/imsgTests/CommandTests.swift
index c389875..4e32761 100644
--- a/Tests/imsgTests/CommandTests.swift
+++ b/Tests/imsgTests/CommandTests.swift
@@ -100,7 +100,9 @@ func chatsCommandRunsWithJsonOutput() async throws {
     flags: ["jsonOutput"]
   )
   let runtime = RuntimeOptions(parsedValues: values)
-  try await ChatsCommand.spec.run(values, runtime)
+  _ = try await StdoutCapture.capture {
+    try await ChatsCommand.spec.run(values, runtime)
+  }
 }
 
 @Test
@@ -112,7 +114,9 @@ func historyCommandRunsWithChatID() async throws {
     flags: ["jsonOutput"]
   )
   let runtime = RuntimeOptions(parsedValues: values)
-  try await HistoryCommand.spec.run(values, runtime)
+  _ = try await StdoutCapture.capture {
+    try await HistoryCommand.spec.run(values, runtime)
+  }
 }
 
 @Test
@@ -124,7 +128,9 @@ func historyCommandRunsWithAttachmentsNonJson() async throws {
     flags: ["attachments"]
   )
   let runtime = RuntimeOptions(parsedValues: values)
-  try await HistoryCommand.spec.run(values, runtime)
+  _ = try await StdoutCapture.capture {
+    try await HistoryCommand.spec.run(values, runtime)
+  }
 }
 
 @Test
@@ -136,7 +142,9 @@ func chatsCommandRunsWithPlainOutput() async throws {
     flags: []
   )
   let runtime = RuntimeOptions(parsedValues: values)
-  try await ChatsCommand.spec.run(values, runtime)
+  _ = try await StdoutCapture.capture {
+    try await ChatsCommand.spec.run(values, runtime)
+  }
 }
 
 @Test
@@ -204,7 +212,9 @@ func watchCommandRejectsInvalidDebounce() async {
   )
   let runtime = RuntimeOptions(parsedValues: values)
   do {
-    try await WatchCommand.spec.run(values, runtime)
+    _ = try await StdoutCapture.capture {
+      try await WatchCommand.spec.run(values, runtime)
+    }
     #expect(Bool(false))
   } catch let error as ParsedValuesError {
     #expect(error.description.contains("Invalid value"))
@@ -251,12 +261,14 @@ func watchCommandRunsWithStubStream() async throws {
         continuation.finish()
       }
     }
-  try await WatchCommand.run(
-    values: values,
-    runtime: runtime,
-    storeFactory: { _ in store },
-    streamProvider: streamProvider
-  )
+  _ = try await StdoutCapture.capture {
+    try await WatchCommand.run(
+      values: values,
+      runtime: runtime,
+      storeFactory: { _ in store },
+      streamProvider: streamProvider
+    )
+  }
 }
 
 @Test
@@ -320,12 +332,14 @@ func watchCommandRunsWithJsonOutput() async throws {
         continuation.finish()
       }
     }
-  try await WatchCommand.run(
-    values: values,
-    runtime: runtime,
-    storeFactory: { _ in store },
-    streamProvider: streamProvider
-  )
+  _ = try await StdoutCapture.capture {
+    try await WatchCommand.run(
+      values: values,
+      runtime: runtime,
+      storeFactory: { _ in store },
+      streamProvider: streamProvider
+    )
+  }
 }
 
 @Test