diff --git a/swh/indexer/codemeta.py b/swh/indexer/codemeta.py
--- a/swh/indexer/codemeta.py
+++ b/swh/indexer/codemeta.py
@@ -30,6 +30,8 @@
 }
 CODEMETA_URI = "https://codemeta.github.io/terms/"
 SCHEMA_URI = "http://schema.org/"
+FORGEFED_URI = "https://forgefed.org/ns#"
+ACTIVITYSTREAMS_URI = "https://www.w3.org/ns/activitystreams#"
 
 
 PROPERTY_BLACKLIST = {
diff --git a/swh/indexer/metadata_dictionary/base.py b/swh/indexer/metadata_dictionary/base.py
--- a/swh/indexer/metadata_dictionary/base.py
+++ b/swh/indexer/metadata_dictionary/base.py
@@ -5,7 +5,7 @@
 
 import json
 import logging
-from typing import Any, Dict, List, Optional, Tuple
+from typing import Any, Callable, Dict, List, Optional, Tuple, TypeVar
 
 from typing_extensions import TypedDict
 
@@ -20,6 +20,26 @@
     type: str
 
 
+TTranslateCallable = TypeVar(
+    "TTranslateCallable", bound=Callable[[Any, Dict[str, Any], Any], None]
+)
+
+
+def mark_productions(
+    namespace: str, terms: List[str]
+) -> Callable[[TTranslateCallable], TTranslateCallable]:
+    """Returns a decorator that marks the decorated function as adding
+    the given terms to the ``translated_metadata`` dict"""
+
+    def decorator(f: TTranslateCallable) -> TTranslateCallable:
+        if not hasattr(f, "produced_terms"):
+            f.produced_terms = []  # type: ignore
+        f.produced_terms.extend(namespace + term for term in terms)  # type: ignore
+        return f
+
+    return decorator
+
+
 class BaseMapping:
     """Base class for mappings to inherit from
 
@@ -103,14 +123,24 @@
 
     @classmethod
     def supported_terms(cls):
-        return {
+        # one-to-one mapping from the original key to a CodeMeta term
+        simple_terms = {
             term
             for (key, term) in cls.mapping.items()
             if key in cls.string_fields
             or hasattr(cls, "normalize_" + cls._normalize_method_name(key))
-            or hasattr(cls, "translate_" + cls._normalize_method_name(key))
         }
 
+        # more complex mapping from the original key to JSON-LD
+        complex_terms = {
+            term
+            for meth_name in dir(cls)
+            if meth_name.startswith("translate_")
+            for term in getattr(getattr(cls, meth_name), "produced_terms", [])
+        }
+
+        return simple_terms | complex_terms
+
     def _translate_dict(
         self, content_dict: Dict, *, normalize: bool = True
     ) -> Dict[str, str]:
diff --git a/swh/indexer/metadata_dictionary/github.py b/swh/indexer/metadata_dictionary/github.py
--- a/swh/indexer/metadata_dictionary/github.py
+++ b/swh/indexer/metadata_dictionary/github.py
@@ -3,12 +3,12 @@
 # License: GNU General Public License version 3, or any later version
 # See top-level LICENSE file for more information
 import json
-from typing import List, Tuple
+from typing import Any, Dict, List, Tuple
 
-from swh.indexer.codemeta import SCHEMA_URI
+from swh.indexer.codemeta import ACTIVITYSTREAMS_URI, FORGEFED_URI, SCHEMA_URI
 from swh.indexer.storage.interface import Sha1
 
-from .base import DirectoryLsEntry, JsonMapping
+from .base import DirectoryLsEntry, JsonMapping, mark_productions
 
 
 def _prettyprint(d):
@@ -31,6 +31,38 @@
     def extrinsic_metadata_formats(cls) -> Tuple[str, ...]:
         return ("application/vnd.github.v3+json",)
 
+    def _translate_dict(self, content_dict: Dict[str, Any], **kwargs) -> Dict[str, Any]:
+        d = super()._translate_dict(content_dict, **kwargs)
+        d["type"] = FORGEFED_URI + "Repository"
+        return d
+
+    @mark_productions(FORGEFED_URI, ["forks"])
+    @mark_productions(ACTIVITYSTREAMS_URI, ["totalItems"])
+    def translate_forks_count(
+        self, translated_metadata: Dict[str, Any], v: Any
+    ) -> None:
+        """
+
+        >>> translated_metadata = {}
+        >>> GitHubMapping().translate_forks_count(translated_metadata, 42)
+        >>> _prettyprint(translated_metadata)
+        {
+            "https://forgefed.org/ns#forks": [
+                {
+                    "@type": "https://www.w3.org/ns/activitystreams#OrderedCollection",
+                    "https://www.w3.org/ns/activitystreams#totalItems": 42
+                }
+            ]
+        }
+        """
+        if isinstance(v, int):
+            translated_metadata.setdefault(FORGEFED_URI + "forks", []).append(
+                {
+                    "@type": ACTIVITYSTREAMS_URI + "OrderedCollection",
+                    ACTIVITYSTREAMS_URI + "totalItems": v,
+                }
+            )
+
     def normalize_license(self, d):
         """
 
diff --git a/swh/indexer/tests/metadata_dictionary/test_github.py b/swh/indexer/tests/metadata_dictionary/test_github.py
--- a/swh/indexer/tests/metadata_dictionary/test_github.py
+++ b/swh/indexer/tests/metadata_dictionary/test_github.py
@@ -21,7 +21,12 @@
 
 def test_supported_terms():
     terms = MAPPINGS["GitHubMapping"].supported_terms()
-    assert {"http://schema.org/name", "http://schema.org/license"} <= terms
+    assert {
+        "http://schema.org/name",
+        "http://schema.org/license",
+        "https://forgefed.org/ns#forks",
+        "https://www.w3.org/ns/activitystreams#totalItems",
+    } <= terms
 
 
 def test_compute_metadata_github():
@@ -107,7 +112,11 @@
     result = MAPPINGS["GitHubMapping"]().translate(content)
     assert result == {
         "@context": "https://doi.org/10.5063/schema/codemeta-2.0",
-        "type": "SoftwareSourceCode",
+        "type": "https://forgefed.org/ns#Repository",
+        "https://forgefed.org/ns#forks": {
+            "https://www.w3.org/ns/activitystreams#totalItems": 1,
+            "type": "https://www.w3.org/ns/activitystreams#OrderedCollection",
+        },
         "license": "https://spdx.org/licenses/GPL-3.0",
         "name": "swh-indexer",
     }