diff --git a/code/backend/Cleanuparr.Api.Tests/Features/QueueCleaner/QueueCleanerResponseContractTests.cs b/code/backend/Cleanuparr.Api.Tests/Features/QueueCleaner/QueueCleanerResponseContractTests.cs
new file mode 100644
index 00000000..99032f2c
--- /dev/null
+++ b/code/backend/Cleanuparr.Api.Tests/Features/QueueCleaner/QueueCleanerResponseContractTests.cs
@@ -0,0 +1,192 @@
+using Cleanuparr.Api.Features.QueueCleaner.Contracts.Requests;
+using Cleanuparr.Api.Features.QueueCleaner.Controllers;
+using Cleanuparr.Api.Tests.TestHelpers;
+using Cleanuparr.Domain.Enums;
+using Cleanuparr.Infrastructure.Models;
+using Cleanuparr.Infrastructure.Services.Interfaces;
+using Cleanuparr.Persistence;
+using Cleanuparr.Persistence.Models.Configuration.QueueCleaner;
+using Microsoft.AspNetCore.Mvc;
+using Microsoft.Extensions.Logging;
+using NSubstitute;
+using Shouldly;
+using Xunit;
+
+namespace Cleanuparr.Api.Tests.Features.QueueCleaner;
+
+/// <summary>
+/// Records today's wire shape, leaks included.
+/// </summary>
+public class QueueCleanerResponseContractTests : IDisposable
+{
+    private readonly DataContext _dataContext;
+    private readonly QueueCleanerConfigController _configController;
+    private readonly QueueRulesController _rulesController;
+
+    public QueueCleanerResponseContractTests()
+    {
+        _dataContext = ConfigControllerTestDataFactory.CreateDataContext();
+
+        _configController = new QueueCleanerConfigController(
+            Substitute.For<ILogger<QueueCleanerConfigController>>(),
+            _dataContext,
+            Substitute.For<IJobManagementService>());
+        ConfigControllerTestDataFactory.ConfigureProblemDetails(_configController);
+
+        IRuleIntervalValidator validator = Substitute.For<IRuleIntervalValidator>();
+        validator.ValidateStallRuleIntervals(Arg.Any<StallRule>(), Arg.Any<List<StallRule>>())
+            .Returns(ValidationResult.Success());
+        validator.ValidateSlowRuleIntervals(Arg.Any<SlowRule>(), Arg.Any<List<SlowRule>>())
+            .Returns(ValidationResult.Success());
+
+        _rulesController = new QueueRulesController(
+            Substitute.For<ILogger<QueueRulesController>>(),
+            _dataContext,
+            validator);
+        ConfigControllerTestDataFactory.ConfigureProblemDetails(_rulesController);
+    }
+
+    public void Dispose()
+    {
+        _dataContext.Dispose();
+        GC.SuppressFinalize(this);
+    }
+
+    [Fact]
+    public async Task GetQueueCleanerConfig_ReturnsTheDocumentedKeys()
+    {
+        IActionResult result = await _configController.GetQueueCleanerConfig();
+
+        ResponseContract.Keys(result).ShouldBe(
+        [
+            "cronExpression",
+            "downloadingMetadataMaxStrikes",
+            "enabled",
+            "failedImport",
+            "id",
+            "ignoredDownloads",
+            "processNoContentId",
+            "slowRules",
+            "stallRules",
+            "useAdvancedScheduling",
+        ]);
+    }
+
+    [Fact]
+    public async Task GetStallRules_ReturnsTheDocumentedKeys()
+    {
+        await _rulesController.CreateStallRule(NewStallDto("contract"));
+
+        IActionResult result = await _rulesController.GetStallRules();
+
+        ResponseContract.FirstItemKeys(result).ShouldBe(StallRuleKeys);
+    }
+
+    [Fact]
+    public async Task CreateStallRule_ReturnsTheDocumentedKeys()
+    {
+        IActionResult result = await _rulesController.CreateStallRule(NewStallDto("contract"));
+
+        ResponseContract.Keys(result).ShouldBe(StallRuleKeys);
+    }
+
+    [Fact]
+    public async Task UpdateStallRule_ReturnsTheDocumentedKeys()
+    {
+        IActionResult created = await _rulesController.CreateStallRule(NewStallDto("contract"));
+        Guid id = created.ShouldBeOfType<CreatedAtActionResult>().Value.ShouldBeOfType<StallRule>().Id;
+
+        IActionResult result = await _rulesController.UpdateStallRule(id, NewStallDto("renamed"));
+
+        ResponseContract.Keys(result).ShouldBe(StallRuleKeys);
+    }
+
+    [Fact]
+    public async Task GetSlowRules_ReturnsTheDocumentedKeys()
+    {
+        await _rulesController.CreateSlowRule(NewSlowDto("contract"));
+
+        IActionResult result = await _rulesController.GetSlowRules();
+
+        ResponseContract.FirstItemKeys(result).ShouldBe(SlowRuleKeys);
+    }
+
+    [Fact]
+    public async Task CreateSlowRule_ReturnsTheDocumentedKeys()
+    {
+        IActionResult result = await _rulesController.CreateSlowRule(NewSlowDto("contract"));
+
+        ResponseContract.Keys(result).ShouldBe(SlowRuleKeys);
+    }
+
+    [Fact]
+    public async Task UpdateSlowRule_ReturnsTheDocumentedKeys()
+    {
+        IActionResult created = await _rulesController.CreateSlowRule(NewSlowDto("contract"));
+        Guid id = created.ShouldBeOfType<CreatedAtActionResult>().Value.ShouldBeOfType<SlowRule>().Id;
+
+        IActionResult result = await _rulesController.UpdateSlowRule(id, NewSlowDto("renamed"));
+
+        ResponseContract.Keys(result).ShouldBe(SlowRuleKeys);
+    }
+
+    private static readonly string[] StallRuleKeys =
+    [
+        "changeCategory",
+        "deletePrivateTorrentsFromClient",
+        "enabled",
+        "id",
+        "maxCompletionPercentage",
+        "maxStrikes",
+        "minCompletionPercentage",
+        "minimumProgress",
+        "name",
+        "privacyType",
+        "queueCleanerConfig",
+        "queueCleanerConfigId",
+        "resetStrikesOnProgress",
+    ];
+
+    private static readonly string[] SlowRuleKeys =
+    [
+        "changeCategory",
+        "deletePrivateTorrentsFromClient",
+        "enabled",
+        "id",
+        "ignoreAboveSize",
+        "ignoreWhileAltSpeedActive",
+        "maxCompletionPercentage",
+        "maxStrikes",
+        "maxTimeHours",
+        "minCompletionPercentage",
+        "minSpeed",
+        "name",
+        "privacyType",
+        "queueCleanerConfig",
+        "queueCleanerConfigId",
+        "resetStrikesOnProgress",
+    ];
+
+    private static StallRuleDto NewStallDto(string name) => new()
+    {
+        Name = name,
+        Enabled = true,
+        MaxStrikes = 3,
+        PrivacyType = TorrentPrivacyType.Public,
+        MinCompletionPercentage = 0,
+        MaxCompletionPercentage = 100,
+        ResetStrikesOnProgress = true,
+    };
+
+    private static SlowRuleDto NewSlowDto(string name) => new()
+    {
+        Name = name,
+        Enabled = true,
+        MaxStrikes = 3,
+        PrivacyType = TorrentPrivacyType.Public,
+        MinCompletionPercentage = 0,
+        MaxCompletionPercentage = 100,
+        ResetStrikesOnProgress = true,
+        MinSpeed = "1MB",
+    };
+}
diff --git a/code/backend/Cleanuparr.Api.Tests/TestHelpers/ResponseContract.cs b/code/backend/Cleanuparr.Api.Tests/TestHelpers/ResponseContract.cs
new file mode 100644
index 00000000..52060b75
--- /dev/null
+++ b/code/backend/Cleanuparr.Api.Tests/TestHelpers/ResponseContract.cs
@@ -0,0 +1,61 @@
+using System.Text.Json;
+using Cleanuparr.Api.Json;
+using Microsoft.AspNetCore.Mvc;
+
+namespace Cleanuparr.Api.Tests.TestHelpers;
+
+/// <summary>
+/// Serializes a controller result through the API's own JSON options.
+/// </summary>
+public static class ResponseContract
+{
+    private static readonly JsonSerializerOptions Options = BuildOptions();
+
+    private static JsonSerializerOptions BuildOptions()
+    {
+        JsonSerializerOptions options = new(JsonSerializerDefaults.Web);
+        CleanuparrJsonConfiguration.ConfigureApiInbound(options);
+        return options;
+    }
+
+    /// <summary>
+    /// Serializes the value carried by an <see cref="ObjectResult"/> and parses it back.
+    /// </summary>
+    public static JsonElement Body(IActionResult result)
+    {
+        if (result is not ObjectResult objectResult)
+        {
+            throw new InvalidOperationException($"Expected an ObjectResult, got {result.GetType().Name}.");
+        }
+
+        if (objectResult.Value is null)
+        {
+            throw new InvalidOperationException("The result carries no value.");
+        }
+
+        string json = JsonSerializer.Serialize(objectResult.Value, objectResult.Value.GetType(), Options);
+        return JsonDocument.Parse(json).RootElement.Clone();
+    }
+
+    /// <summary>
+    /// Top-level property names, sorted so assertions read in a stable order.
+    /// </summary>
+    public static IReadOnlyList<string> Keys(IActionResult result) => Keys(Body(result));
+
+    /// <inheritdoc cref="Keys(IActionResult)" />
+    public static IReadOnlyList<string> Keys(JsonElement element) =>
+        element.EnumerateObject()
+            .Select(property => property.Name)
+            .OrderBy(name => name, StringComparer.Ordinal)
+            .ToList();
+
+    /// <summary>
+    /// Property names of the first array element, empty when the array is empty.
+    /// </summary>
+    public static IReadOnlyList<string> FirstItemKeys(IActionResult result)
+    {
+        JsonElement body = Body(result);
+        JsonElement? first = body.EnumerateArray().Cast<JsonElement?>().FirstOrDefault();
+        return first is null ? [] : Keys(first.Value);
+    }
+}