rea/docs/il2cpp-metadata.md

IL2CPP metadata

inspect_il2cpp_metadata / inspect-il2cpp-metadata decodes one selected local Unity IL2CPP global-metadata.dat file and returns its assembly images, type definitions and method definitions by name, namespace, index range and count, with the header sections and serialized index widths. It reads the file without running it and requires no Unity installation, IL2CPP binary, active target, Hopper, Ghidra or IDA.

Metadata versions 29, 31 and 39 are supported. For example, Unity 2022.3.30f1 wrote version 29, 2022.3.62f3 wrote 31 and 6000.4.2f1 wrote 39; other Unity releases that write these numbers have not been checked. Other versions are rejected as unsupported. The path must name a regular file; directories and symbolic links are rejected.

MCP

MCP defaults to a compact summary and retains the complete decoded Evidence in the session. MCP requires an absolute filesystem path:

{
  "name": "inspect_il2cpp_metadata",
  "arguments": {
    "path": "/artifacts/Data/Managed/Metadata/global-metadata.dat"
  }
}

The summary retains the complete decoded Evidence in the session and returns a linked inspect_analysis_view overview: artifact identity, metadata version, index widths and counts (sections, images, types, methods and nested_types) without rows. Use normalized_result.parent_evidence_id to page the original rows without reopening or decoding the file:

{
  "source": {
    "kind": "retained-evidence",
    "evidence_id": "<parent_evidence_id>"
  },
  "view": {
    "kind": "il2cpp-metadata",
    "collection": "types",
    "offset": 0,
    "limit": 64
  }
}

Collections are sections, images, types and methods. Every returned row includes its source index, scoped by artifact SHA-256 and collection. All collections accept batch indices, exact names and fields. Types also accept image_indices, namespaces and declaring_types; methods accept declaring_types. Filters intersect, duplicate indices are returned once, and rows retain metadata order. An empty filter selects no rows; fields: [] returns indices only. Omitted fields return the complete selected rows.

For example, after resolving a type index, retrieve selected method facts:

{
  "source": {
    "kind": "retained-evidence",
    "evidence_id": "<parent_evidence_id>"
  },
  "view": {
    "kind": "il2cpp-metadata",
    "collection": "methods",
    "declaring_types": [1555],
    "names": ["SendMessage"],
    "fields": ["name", "declaring_type"]
  }
}

offset counts matching rows, not source indices. limit defaults to 64; coverage.next_offset continues that filtered page. Coverage describes retained metadata facts only; runtime behavior and correspondence to native code remain unknown. Each view preserves the parent Evidence link, artifact identity and limitations. Queries work after the source file is removed. Select detail: "complete" to return every row inline within the separate MCP response budget.

CLI

rea inspect-il2cpp-metadata /absolute/path/global-metadata.dat --json

The CLI defaults to complete Evidence. For compact delivery, explicitly preserve the full Evidence in a new file:

rea inspect-il2cpp-metadata /absolute/path/global-metadata.dat \
  --detail summary --evidence_output /tmp/metadata-evidence.json --json
jq -c '{source: {kind: "inline", evidence: .records[0]}, view: {kind: "il2cpp-metadata", collection: "methods", indices: [9785], fields: ["name", "declaring_type"]}}' \
  /tmp/metadata-evidence.json > /tmp/metadata-query.json
rea inspect-analysis-view /tmp/metadata-query.json --json

Use the exported Evidence with the CLI's inline Evidence source format described in CLI and Evidence. Compact delivery requires --evidence_output; existing files are never overwritten. The full export preserves every decoded row for subsequent queries without the original file.

Observations

The result contains:

• artifact: path, SHA-256 and byte length;
• magic: unsigned little-endian header signature (0xFAB11BAF, delivered as a JSON number);
• metadata_version: 29, 31 or 39;
• index_widths: the serialized widths (1, 2 or 4 bytes) of type_definition, generic_container, parameter and type indices, and type_width_source. Version 39 derives the type index width from the interface-offsets-record or the type-definition-record; versions 29 and 31 always use 4-byte indices (fixed-width-version);
• sections: all 31 header sections in header order, each with offset, size and count. Versions 29 and 31 record no counts, so count is null and record counts come from the section sizes;
• images: name, type_start and type_count;
• types: name, namespace, method_start, method_count, nested_type_start, nested_type_count and declaring_type;
• methods: name and declaring_type;
• limitations.

A row's position in its collection is its metadata index, so type_start, method_start and declaring_type refer to positions in types or methods. nested_type_start instead indexes the metadata's nestedTypes table, which is not returned; each nested type's declaring_type carries that relationship. A type's declaring_type is derived from the nestedTypes section and is -1 for top-level types. The start of an empty range can retain the original value -1.

The complete inventory of a large game is several megabytes and can exceed the MCP response budget. Summary delivery and filtered, projected pages keep unneeded rows out of agent context without discarding the source Evidence.

Failures

A file whose magic is not 0xFAB11BAF fails as an unsupported target with unrecognized-magic. The file may be encrypted or may not be IL2CPP metadata. A version other than 29, 31 or 39 fails as an unsupported target with unsupported-version.

Damaged metadata returns an input error (invalid_format) whose message names one reason:

Reason	Meaning
truncated-header	The file is shorter than the header.
unexpected-header-size	stringLiterals.offset is not the header size: 256 bytes for versions 29 and 31, 380 for 39.
section-out-of-bounds	A section extends beyond the file, or a non-empty section starts inside the header.
section-overlap	Two sections overlap. Zero-size sections are exempt and gaps are allowed.
record-size-mismatch	A section size does not divide into its records, or the record size differs from the one the index widths imply.
type-index-width	The record used to derive the type index width implies no 1, 2 or 4 byte width.
index-out-of-range	A serialized index or range points outside its target collection.
nested-type-conflict	A type is listed as nested in two types, in itself, or in a cycle of declaring types.
declaring-type-mismatch	A method inside a type's method range names a different type, or a method lies outside its type's range.
image-range-overlap	Two images claim the same type definitions.
invalid-string	A name index does not start a string, or the name is unterminated or not valid UTF-8.

A version field that disagrees with the file's layout, for example a version 39 file relabeled as 29, usually surfaces as unexpected-header-size or record-size-mismatch.

Two checks are stricter than the IL2CPP runtime: a name index must start a string, and an empty range's start must lie between -1 and the collection size. Every Unity-written file checked so far satisfies both; metadata rewritten by other tools may be rejected.

An incomplete inventory is never reported as complete. Failures after a verified snapshot retain partial source Evidence with its SHA-256, byte length and any validated section row counts; these counts do not establish that names and relationships were decoded. A file that changes during reading and a cancelled request keep distinct errors. Decode checkpoints yield for cancellation, and close waits for active work. Each reader admits one inspection at a time. Resource guards bound the selected file to 256 MiB and the encoded complete report to 64 MiB, checking JSON/UTF-8 expansion before serialization. MCP also applies its response transport budget; a complete report within the report limit can still require the summary and paging path.

Outside this tool

• Decrypting or deobfuscating protected metadata.
• Linking metadata to the native binary (GameAssembly, UnityFramework), including method RVAs and code addresses.
• Fields, properties, signatures, parameters and generic instances.
• Ghidra or other disassembler integration. Use the native workflow for native code.
• Metadata versions other than 29, 31 and 39.

Names come from the metadata file only. They do not establish which methods were compiled into the native binary or how they behave at runtime.

Real producer verification

npm run verify:il2cpp:metadata -- --metadata PATH exercises a caller-supplied global-metadata.dat through the public CLI and MCP. It is opt-in, like verify:pcap, because no real game metadata ships with the repository. Normal inspection does not need it.

The follow-up was checked against the public Cpp2IL Simple_2022_3_35 sample: version 31, 1,892,268 bytes, SHA-256 2441635a7c234a1a34deccc6a9906d6f5abcbdab078a38b2bf488a52a4962c48. An independent byte-layout oracle matched all 36 images, 2,468 types and 12,409 methods. Corresponding managed DLLs independently matched names and ownership for 35 images, 2,463 types and 12,406 methods; the generated image has no matching DLL. This does not establish real-producer coverage for versions 29 or 39.