MCPDevTools User Guide

MCPDevTools provides asset queries, editing, and read-only development diagnostics over HTTP MCP in Unreal Editor. It currently registers 33 tools: the original 30 asset tools plus GetDevContext, ListProjectPlugins, and ReadDevLog. Use the tools/list response and tool results from the target editor as the authority.

Place Plugins/MCPDevTools in your project’s Plugins directory and enable MCPDevTools in the .uproject Plugins array. After opening the editor, configure the port and automatic startup under Project Settings → Plugins → MCPDevTools. The default address is http://127.0.0.1:8768/mcp. If the port is occupied, the server tries subsequent ports; use the actual address in the editor log. InputAction and InputMappingContext tools also require EnhancedInput. Creating either asset type requires the InputEditor module.

AssetPath is a package path such as /Game/Data/DA_Example, not a short name, object path, or subobject path. ClassPath is a full class object path, such as /Script/Engine.DataAsset or a compiled Blueprint class path like /Game/Data/BP_Example.BP_Example_C. Standard lists and paged reads return 20 items by default, with at most 100 per page. Continue using bHasMore and NextOffset. Editing supports seven asset categories: DataAsset, DataTable, Curve, CurveTable, StringTable, PrimaryAssetLabel, and Enhanced Input (InputAction/InputMappingContext).

The three diagnostic tools do not start processes or test jobs, load assets, save packages, or change configuration. Their inputs reject extra fields. Missing context returns a specific reason for unavailability.

ListProjectPlugins and ReadDevLog default to 100 items per page, with a maximum of 200. Continue with the returned NextCursor. Log pages also reserve a serialization budget for worst-case JSON escaping, with a maximum TextContent length of 512 Ki TCHAR. A page may therefore contain fewer entries than Limit; matching entries that were not returned remain available on the next page. Plugin lists return only the name, friendly name, version number/name, enabled state, source, and type. They do not return arbitrary descriptor JSON or plugin paths. List cursors are bound to a snapshot, Scope, and Limit. If the information or query conditions change, restart the query without Cursor.

Logs exist only in the current process’s memory, with limits of 2,048 entries, 2 MiB of total text, and 8,192 TCHAR per entry. VerbosityFilter accepts Fatal, Error, Warning, Display, Log, Verbose, and VeryVerbose; omitting it or passing an empty array disables level filtering. Output includes CaptureStartUtc, CaptureSession, NextCursor, coverage-gap fields bGap / DroppedSinceCursor, and the truncation flag bTruncated. Even when no logs match, the cursor advances to the position already examined. Cursors from an earlier capture session are rejected, and the first read may already have a coverage gap. Module shutdown stops capture and unregisters the output device. The tool provides no disk logs, history from before registration, or guarantee of complete capture during a crash. Plugin logs produced by HTTP queries may appear on subsequent pages. Messages in this category may contain project names or paths; logs are not guaranteed to be free of private information.

On Windows, listener results come from read-only GetExtendedTcpTable observations of the current PID and ActualPort for IPv4/IPv6. observed_loopback requires both address-family queries to succeed and every matching address to be in IPv4 127/8 or IPv6 ::1; wildcard addresses produce observed_non_loopback. Query failure, ambiguous ownership, no matches, or a state change produces unknown; a stopped server produces not_running. Other platforms return the reason unsupported_platform. A returned 127.0.0.1 URL does not itself prove the actual binding. OS observations describe only the sampling instant and provide neither authentication nor an ongoing security guarantee. The tools do not change listeners, HTTP settings, firewalls, or permissions.

1. Use the relevant Get... tool to read the complete current values. If the type or fields are unclear, call GetAssetTypeSchema. For creation, keep the default bDryRun=true first, check the path, class, or mode, then set bDryRun=false.
2. For edits, copy the complete old values into the corresponding Expected... parameters and provide the new values. Start with the default dry-run, then set bDryRun=false. Conflicts or invalid fields cause rejection. Created or edited assets are dirty in memory.
3. Once you have checked the result, call SaveAsset separately to write that asset package. Tools do not automatically check out files, overwrite an existing creation path, or save referenced assets.

Existing DataAsset calls remain unchanged. For example, after GetDataAsset returns "Old" as the current Title, call SetDataAssetProperties:

{
  "AssetPath": "/Game/Data/DA_Example",
  "Properties": { "Title": "New" },
  "ExpectedValues": { "Title": "Old" },
  "bDryRun": true
}

Input Trigger, Modifier, and PlayerMappable settings are instances owned by the asset, rather than ordinary object references. Replace an instance using the shape { "ClassPath": "/Script/EnhancedInput.InputTriggerHold", "Properties": {} }. Arrays retain input order, and PlayerMappableKeySettings accepts that object shape or null. Each InputMappingContext mapping contains Properties, Triggers, and Modifiers, with optional PlayerMappableKeySettings. MappingProfileOverrides is an object mapping profile names to complete mapping arrays. UE 5.8 exposes profiles; UE 5.2 has no such field and rejects profile parameters. First read bProfileOverridesSupported and the complete old values for the current engine from GetInputMappingContext.

• Writable types include booleans, finite numbers within the type’s range, valid enum names, strings, names, value-type structs, arrays, sets, Maps with string or name keys, and hard/soft object and class references. Read and write 64-bit integers beyond JSON’s exact integer range as decimal strings. Structs may omit unchanged fields; arrays, Sets, and Maps are replaced in full.
• Read and write FText as an identity object: {"InvariantText":"内容"}, {"StringTableId":"...","StringTableKey":"..."}, or the localized form {"Namespace":"...","Key":"...","Source":"..."}. The localized form in UE 5.8 also includes DevNotes. Text that cannot be represented losslessly, such as formatted or numeric text, is read-only.
• Field names are case-sensitive. JSON objects must not contain duplicate keys or keys that differ only in case. Property names, enum names, FName values and keys, and paths reject embedded NUL. Ordinary string values are compared at their full length. Duplicate Set values and Map-key normalization collisions are rejected.
• Ordinary property references use a full path to an existing object of the matching type, or JSON null to clear the value. Generic DataAsset property editing does not accept inline subobjects, delegates, Transient or read-only fields, or unsupported types. Use the dedicated parameters above for Input instances.
• ListDataAssets filters ClassPath by inheritance and accepts abstract DataAsset base classes such as DataAsset and PrimaryDataAsset. Class-path requirements and the requirement for a currently successful Blueprint compile still apply. CreateDataAsset requires a concrete, non-abstract class and uses the generic DataAsset factory. Use the corresponding creation tool for types requiring a dedicated factory. SaveAsset saves only supported single-asset packages; read-only files are rejected.

Behavior on other platforms, native Manage/SearchableName dependency edges, Cook/actual Chunk output, and non-empty ExplicitBlueprints remains unconfirmed. The current tools do not provide Automation/Build/Cook/Package jobs, arbitrary commands, or editing of user C++ source code.