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Engine Source Index

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tumourlove edited this page Jun 13, 2026 · 7 revisions

Engine Source Index

Monolith includes a native C++ source indexer that runs automatically on editor startup. No Python, no external tools, no setup required. It indexes the entire UE engine source tree into a local SQLite database, enabling instant API lookups, call graphs, and class hierarchy queries.

How It Works

  1. Automatic on startup — The native indexer runs inside the editor when it first launches. No separate script to run.
  2. 1M+ symbols indexed — full class definitions, inheritance links, call graphs. As of the v0.19.0 allman-brace parser fix the engine symbols table tripled (~301K → ~967K rows) — see the note below.
  3. Database — Stored in Saved/Monolith/EngineSource.db.
  4. Fully offline — All queries run against the local SQLite database. No network access needed.

v0.19.0 — plain-class indexing gap fixed. The non-reflected class/struct extractor used to require the opening { on the declaration line, but Epic's coding standard puts it on the next line (allman). That structurally excluded the vast majority of exported non-reflected engine types — FCollisionShape, FSceneView, FPrimitiveSceneProxy, FScopeLock, FPaths, FRegexPattern and ~40K others had no row and no extracted members, so get_include_path, read_source, get_class_hierarchy, verify_symbols, get_signature, and find_example_usage all degraded or failed on them. The parser now accepts the allman brace. Existing EngineSource.db files enrich on the next full trigger_reindex — the offline tools then return the richer results automatically.

Available Actions (20)

Action Description
read_source Full source code for any class (or members_only mode for just the interface)
find_references Type references across the engine codebase
find_callers Who calls a given function
find_callees What a function calls
search_source Full-text search across all indexed source (cursor-paginated)
get_class_hierarchy Ancestors and descendants with configurable depth
get_module_info Module path, type, file count, key classes
get_symbol_context Definition with surrounding context lines
read_file Raw source file by relative path
trigger_reindex Re-run the engine source indexer
trigger_project_reindex Incremental re-index of project C++ source
audit_module_dep_reality Find UE type references whose declaring module is missing from the file's Build.cs deps (the LNK2019 bug class)

LLM C++ authoring ergonomics (v0.19.0, 8 actions)

Read-only, offline-served lookups so an AI agent resolves an include, signature, deprecation, or Build.cs dep in one round-trip instead of reading raw source.

Action Description
get_include_path Canonical #include for a symbol (resolves via the owning class header). Public/Classes/Internal headers are includable cross-module; Private headers report includable:false with a same-module note
get_signature Exact declaration signature(s) for a function or Class::Method, with inline bodies + macro line-continuations stripped. Overloads returned separately
check_deprecations Batch UE_DEPRECATED status for a symbols[] list. Returns index_state:"empty" (never a false clean bill) if the deprecation index hasn't been built by a reindex yet
verify_symbols Batch pre-flight verdict — existence + include + signature + deprecation composed per symbol. A missing symbol reports exists:false, no error
find_example_usage Ranked real call-site examples via source-line FTS, ±3 lines of context, prefer engine/project ranking, cursor-paginated
suggest_build_cs_deps Suggest Build.cs PrivateDependencyModuleNames for a file (or symbol list). Reads the declaring module's Build.cs from disk — works on uncommitted files
lint_header Regex-level UHT-gotcha lint of a single header — works on unindexed files you just wrote
generate_class_stub UCLASS-derived .h/.cpp stub pair returned as TEXT (never writes to disk)

Optional: Index Your Project's C++ Source

Engine source indexing is automatic. If you also want your own project's C++ source indexed (so find_callers/find_callees/get_class_hierarchy span your project code too):

  1. Install Python 3.10+
  2. Run python Plugins/Monolith/Scripts/index_project.py from your project root
  3. Your source gets added to EngineSource.db alongside engine symbols
  4. The database grows by your project's source footprint (the engine portion is ~7 GB after the v0.19.0 plain-class indexing expansion)
  5. To re-run without leaving the editor: source_query("trigger_project_reindex")

The project indexer is incremental — only changed files are reprocessed on subsequent runs.

Offline Queries (Editor Not Running)

When the editor is down, use the standalone monolith_query.exe to query the same databases. Zero UE dependency, instant startup.

# Search engine source
Plugins/Monolith/Binaries/monolith_query.exe source search_source FCharacterMovementComponent --limit=5

# Read a class
Plugins/Monolith/Binaries/monolith_query.exe source read_source ACharacter --max-lines=50

# Class hierarchy
Plugins/Monolith/Binaries/monolith_query.exe source get_class_hierarchy ACharacter --depth=3 --direction=down

# Project asset search
Plugins/Monolith/Binaries/monolith_query.exe project search damage --limit=10

monolith_offline.py (Scripts/monolith_offline.py) is a maintained stdlib-only dev fallback for the exe, kept byte-identical to it. Both offline tools serve the full Reflection-Intelligence surface (cppreflect, network, decision, risk) byte-identical to the live MCP server. The exe auto-detects database paths relative to its own location.

Usage Tips

  • Always use source_query when debugging — never guess UE API signatures, include paths, or function names
  • read_source with members_only: true — returns the class interface without function bodies, much more compact
  • find_callers/find_callees — great for understanding how engine systems interact
  • get_class_hierarchy — trace inheritance from any class up or down the tree

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