unreal-api-mcp 0.1.0

MCP server providing ground-truth Unreal Engine API documentation -- prevents AI hallucination of signatures, includes, and deprecated APIs

unreal-api-mcp

MCP server that gives AI agents accurate Unreal Engine C++ API documentation. Prevents hallucinated signatures, wrong #include paths, and deprecated API usage.

Supports UE 5.5, 5.6, and 5.7 with separate databases for each version. Works with Claude Code, Cursor, Windsurf, or any MCP-compatible AI tool. No Unreal Engine installation required.

Quick Start

pip install unreal-api-mcp

Add to your MCP config (.mcp.json, mcp.json, or your tool's MCP settings), setting UNREAL_VERSION to match your project:

{
  "mcpServers": {
    "unreal-api": {
      "command": "unreal-api-mcp",
      "args": [],
      "env": {
        "UNREAL_VERSION": "5.5"
      }
    }
  }
}

Valid values: "5.5", "5.6", or "5.7". On Windows, use unreal-api-mcp.exe.

On first run the server downloads the correct database (~43-48 MB) to ~/.unreal-api-mcp/.

How It Works

1. Version detection. The server figures out which UE version to serve:

Priority	Source	Example
1	UNREAL_VERSION env var	"5.5", "5.6", "5.7"
2	UNREAL_PROJECT_PATH	Reads .uproject EngineAssociation field, maps 5.5.1 to "5.5"
3	Default	"5.7"

2. Database download. If the database for that version isn't cached locally, it downloads from GitHub (one time).

3. Serve. All tool calls query the version-specific SQLite database. Exact lookups return in <1ms, searches in <5ms.

Each version has its own database with the correct signatures, deprecation warnings, and member lists for that release.

Tools

Tool	Purpose	Example
search_unreal_api	Find APIs by keyword	"character movement", "spawn actor"
get_function_signature	Exact signature with parameters and return type	AActor::GetActorLocation
get_include_path	Resolve #include for a type	"ACharacter" -> #include "GameFramework/Character.h"
get_class_reference	Full class reference card	"APlayerController" -> all functions/properties/delegates
get_deprecation_warnings	Check if an API is obsolete	"K2_AttachRootComponentTo" -> Use AttachToComponent() instead

Coverage

All Engine Runtime, Editor, Developer modules, plus built-in plugins (Enhanced Input, Gameplay Abilities, Common UI, Niagara, Chaos, and hundreds more).

Version	Records	Deprecated	Modules	DB Size
UE 5.5	99,591	3,689	860	43 MB
UE 5.6	109,530	4,205	981	48 MB
UE 5.7	114,724	4,409	1,019	50 MB

Record breakdown (UE 5.7):

Type	Count	Source
Classes (UCLASS)	10,075	AActor, ACharacter, UGameplayStatics, ...
Structs (USTRUCT)	9,014	FHitResult, FVector, FTransform, ...
Enums (UENUM)	3,475	EMovementMode, ECollisionChannel, ...
Functions (UFUNCTION)	23,414	Signatures with params, return types, specifiers
Properties (UPROPERTY)	66,340	Types, specifiers, doc comments
Delegates	2,406	Dynamic multicast, delegate declarations

Does not cover third-party plugins or marketplace assets. For those, rely on project source.

Benchmarks

In a 10-step character movement development workflow, MCP consistently uses far fewer tokens than agents working with grep and file reads:

The gap holds across every question type. MCP wins on simple include lookups and complex class references alike:

Even in a realistic hybrid workflow where MCP results are followed up with targeted file reads, it still uses significantly fewer tokens than a skilled agent working without MCP:

"Without MCP" estimates assume full or partial file reads. A skilled agent with good tooling may use fewer tokens than shown. What MCP guarantees is a correct, structured answer in one call every time.

Per-question breakdown

Query latency

Measured on UE 5.7 database (114,724 records), 50 iterations per query:

Query	Median	p95
Exact FQN lookup (get_function_signature)	<1ms	<1ms
FTS search: specific function name	<1ms	<1ms
FTS search: keyword ("spawn actor")	1ms	1ms
Include path resolution	2ms	2ms
Class reference (full member list)	22ms	23ms
Deprecation check	24ms	25ms

Accuracy

Test	Result
Search top-1 relevance (8 common queries)	100%
Include path resolution (6 key classes)	100%
Function signature accuracy (3 common functions)	100%
Class reference completeness (2 classes)	100%
Deprecation detection (1 deprecated API)	100%

Ranking uses BM25 with tuned column weights (member name 10x, class name 5x) plus core module boosting to ensure AActor::GetActorLocation ranks above niche plugin APIs.

CLAUDE.md Snippet

Add this to your project's CLAUDE.md (or equivalent instructions file). This step is important. Without it, the AI has the tools but won't know when to reach for them.

## Unreal Engine API Lookup (unreal-api MCP)

Use the `unreal-api` MCP tools to verify UE C++ API usage instead of guessing. **Do not hallucinate signatures or #include paths.**

| When | Tool | Example |
|------|------|---------|
| Unsure about a function's parameters or return type | `get_function_signature` | `get_function_signature("AActor::GetActorLocation")` |
| Need the `#include` for a type | `get_include_path` | `get_include_path("ACharacter")` |
| Want to see all members on a class | `get_class_reference` | `get_class_reference("UCharacterMovementComponent")` |
| Searching for an API by keyword | `search_unreal_api` | `search_unreal_api("spawn actor")` |
| Checking if an API is deprecated | `get_deprecation_warnings` | `get_deprecation_warnings("K2_AttachRootComponentTo")` |

**Rules:**
- Before writing a UE API call you haven't used in this conversation, verify the signature with `get_function_signature`
- Before adding a `#include`, verify with `get_include_path` if unsure
- Covers: all Engine Runtime/Editor modules, built-in plugins (Enhanced Input, GAS, CommonUI, Niagara, etc.)
- Does NOT cover: third-party plugins or marketplace assets

Setup Details

Auto-detect version from .uproject

Instead of setting UNREAL_VERSION, you can point to your Unreal project. The server reads the EngineAssociation field from your .uproject file:

{
  "mcpServers": {
    "unreal-api": {
      "command": "unreal-api-mcp",
      "args": [],
      "env": {
        "UNREAL_PROJECT_PATH": "F:/Unreal Projects/MyProject"
      }
    }
  }
}

Environment variables

Variable	Purpose	Example
UNREAL_VERSION	UE version to serve	5.5, 5.6, 5.7
UNREAL_PROJECT_PATH	Auto-detect version from .uproject	F:/Unreal Projects/MyProject
UNREAL_INSTALL_PATH	Override UE install path (for ingest only)	H:/UE_5.6

Building databases locally

If you want to build a database from your own Unreal Engine installation instead of downloading:

# Build for a specific version
python -m unreal_api_mcp.ingest --unreal-version 5.6 --unreal-install "H:/UE_5.6"
python -m unreal_api_mcp.ingest --unreal-version 5.5 --unreal-install "H:/UE_5.5"

Databases are written to ~/.unreal-api-mcp/unreal_docs_{version}.db by default.

Project structure

unreal-api-mcp/
├── src/unreal_api_mcp/
│   ├── server.py          # MCP server (5 tools)
│   ├── db.py              # SQLite + FTS5 database layer
│   ├── version.py         # Version detection + DB download
│   ├── header_parser.py   # Parse Unreal C++ headers (UCLASS, UFUNCTION, etc.)
│   ├── unreal_paths.py    # Locate UE installs + discover modules
│   └── ingest.py          # CLI ingestion pipeline
└── pyproject.toml

Databases are stored in ~/.unreal-api-mcp/ (downloaded on first run).

Troubleshooting

Problem	Fix
"Could not download UE X database"	Check internet connection. Or build locally: python -m unreal_api_mcp.ingest --unreal-version 5.6 --unreal-install H:/UE_5.6
Wrong API version being served	Set UNREAL_VERSION explicitly. Check stderr: unreal-api-mcp: serving UE <version>
Server won't start	Check python --version (needs 3.10+). Check path: which unreal-api-mcp or where unreal-api-mcp
Third-party plugins return no results	Marketplace/third-party plugins are not indexed. Only built-in Engine and Plugin APIs are covered.

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Contact

Need a custom MCP server for your engine or framework? I build MCP tools that cut token waste and prevent hallucinations for AI-assisted game development. If you want something similar for your team's stack, reach out.

[e-mail]

License

MIT