diff --git a/Package.swift b/Package.swift
index 2d0bc86a..130e8536 100644
--- a/Package.swift
+++ b/Package.swift
@@ -416,6 +416,27 @@ let package = Package(
             name: "SocketForwarderTests",
             dependencies: ["SocketForwarder"]
         ),
+        .testTarget(
+            name: "ContainerCommandsTests",
+            dependencies: [
+                "ContainerCommands",
+                "ContainerClient",
+                .product(name: "Containerization", package: "containerization"),
+            ]
+        ),
+        .testTarget(
+            name: "CLITests",
+            dependencies: [
+                .product(name: "AsyncHTTPClient", package: "async-http-client"),
+                .product(name: "Containerization", package: "containerization"),
+                .product(name: "ContainerizationExtras", package: "containerization"),
+                .product(name: "ContainerizationOS", package: "containerization"),
+                "ContainerBuild",
+                "ContainerClient",
+                "ContainerNetworkService",
+            ],
+            path: "Tests/CLITests"
+        ),
         .target(
             name: "ContainerVersion",
             dependencies: [
diff --git a/Sources/ContainerCommands/Container/ContainerKill.swift b/Sources/ContainerCommands/Container/ContainerKill.swift
index c9bfbc20..7d5cac54 100644
--- a/Sources/ContainerCommands/Container/ContainerKill.swift
+++ b/Sources/ContainerCommands/Container/ContainerKill.swift
@@ -50,21 +50,18 @@ extension Application {
         }
 
         public mutating func run() async throws {
-            let set = Set<String>(containerIds)
+            let allContainers = try await ClientContainer.list()
 
-            var containers = try await ClientContainer.list().filter { c in
-                c.status == .running
-            }
-            if !self.all {
-                containers = containers.filter { c in
-                    set.contains(c.id)
-                }
-            }
+            let containersToSignal = try self.all
+                ? allContainers.filter { $0.status == .running }
+                : ContainerStop.containers(matching: containerIds, in: allContainers)
+
+            let runningContainers = containersToSignal.filter { $0.status == .running }
 
             let signalNumber = try Signals.parseSignal(signal)
 
             var failed: [String] = []
-            for container in containers {
+            for container in runningContainers {
                 do {
                     try await container.kill(signalNumber)
                     print(container.id)
diff --git a/Sources/ContainerCommands/Container/ContainerStop.swift b/Sources/ContainerCommands/Container/ContainerStop.swift
index 42cd25f8..966d2a92 100644
--- a/Sources/ContainerCommands/Container/ContainerStop.swift
+++ b/Sources/ContainerCommands/Container/ContainerStop.swift
@@ -21,6 +21,13 @@ import ContainerizationError
 import ContainerizationOS
 import Foundation
 
+package protocol ContainerIdentifiable {
+    var id: String { get }
+    var status: RuntimeStatus { get }
+}
+
+extension ClientContainer: ContainerIdentifiable {}
+
 extension Application {
     public struct ContainerStop: AsyncParsableCommand {
         public init() {}
@@ -45,25 +52,20 @@ extension Application {
         var containerIds: [String] = []
 
         public func validate() throws {
-            if containerIds.count == 0 && !all {
+            if containerIds.isEmpty && !all {
                 throw ContainerizationError(.invalidArgument, message: "no containers specified and --all not supplied")
             }
-            if containerIds.count > 0 && all {
+            if !containerIds.isEmpty && all {
                 throw ContainerizationError(
                     .invalidArgument, message: "explicitly supplied container IDs conflict with the --all flag")
             }
         }
 
         public mutating func run() async throws {
-            let set = Set<String>(containerIds)
-            var containers = [ClientContainer]()
-            if self.all {
-                containers = try await ClientContainer.list()
-            } else {
-                containers = try await ClientContainer.list().filter { c in
-                    set.contains(c.id)
-                }
-            }
+            let allContainers = try await ClientContainer.list()
+            let containers = try self.all
+                ? allContainers
+                : Self.containers(matching: containerIds, in: allContainers)
 
             let opts = ContainerStopOptions(
                 timeoutInSeconds: self.time,
@@ -104,5 +106,19 @@ extension Application {
 
             return failed
         }
+
+        static func containers<C: ContainerIdentifiable>(
+            matching containerIds: [String],
+            in allContainers: [C]
+        ) throws -> [C] {
+            var matched: [C] = []
+            for containerId in containerIds {
+                guard let container = allContainers.first(where: { $0.id == containerId || $0.id.starts(with: containerId) }) else {
+                    throw ContainerizationError(.notFound, message: "no such container: \(containerId)")
+                }
+                matched.append(container)
+            }
+            return matched
+        }
     }
 }
diff --git a/Tests/ContainerCommandsTests/ContainerStopValidationTests.swift b/Tests/ContainerCommandsTests/ContainerStopValidationTests.swift
new file mode 100644
index 00000000..d39f1bf7
--- /dev/null
+++ b/Tests/ContainerCommandsTests/ContainerStopValidationTests.swift
@@ -0,0 +1,61 @@
+//===----------------------------------------------------------------------===//
+// Copyright © 2025 Apple Inc. and the container project authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//   https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//===----------------------------------------------------------------------===//
+
+import ContainerClient
+import ContainerCommands
+import ContainerizationError
+import Testing
+
+@testable import ContainerCommands
+
+struct ContainerStopValidationTests {
+    struct StubContainer: ContainerIdentifiable {
+        let id: String
+        let status: RuntimeStatus
+    }
+
+    @Test
+    func resolvesExactIds() throws {
+        let containers = [StubContainer(id: "abc123", status: .running)]
+        let matched = try Application.ContainerStop.containers(matching: ["abc123"], in: containers)
+        #expect(matched.count == 1)
+        #expect(matched.first?.id == "abc123")
+    }
+
+    @Test
+    func resolvesIdPrefixes() throws {
+        let containers = [
+            StubContainer(id: "abcdef", status: .running),
+            StubContainer(id: "123456", status: .running),
+        ]
+        let matched = try Application.ContainerStop.containers(matching: ["abc"], in: containers)
+        #expect(matched.count == 1)
+        #expect(matched.first?.id == "abcdef")
+    }
+
+    @Test
+    func throwsForMissingContainers() throws {
+        let containers = [StubContainer(id: "abcdef", status: .running)]
+        #expect {
+            _ = try Application.ContainerStop.containers(matching: ["missing"], in: containers)
+        } throws: { error in
+            guard let error = error as? ContainerizationError else {
+                return false
+            }
+            return error.code == .notFound
+        }
+    }
+}