diff --git a/crates/cairo-lang-compiler/src/db.rs b/crates/cairo-lang-compiler/src/db.rs
index 9ea7b152eb0..1be808ec563 100644
--- a/crates/cairo-lang-compiler/src/db.rs
+++ b/crates/cairo-lang-compiler/src/db.rs
@@ -5,8 +5,8 @@ use cairo_lang_defs::db::{DefsDatabase, DefsGroup};
 use cairo_lang_defs::plugin::{InlineMacroExprPlugin, MacroPlugin};
 use cairo_lang_filesystem::cfg::CfgSet;
 use cairo_lang_filesystem::db::{
-    init_dev_corelib, init_files_group, AsFilesGroupMut, FilesDatabase, FilesGroup, FilesGroupEx,
-    CORELIB_CRATE_NAME, CORELIB_VERSION,
+    init_dev_corelib, init_files_group, AsFilesGroupMut, ExternalFiles, FilesDatabase, FilesGroup,
+    FilesGroupEx, CORELIB_CRATE_NAME, CORELIB_VERSION,
 };
 use cairo_lang_filesystem::detect::detect_corelib;
 use cairo_lang_filesystem::flag::Flag;
@@ -38,6 +38,7 @@ pub struct RootDatabase {
     storage: salsa::Storage<RootDatabase>,
 }
 impl salsa::Database for RootDatabase {}
+impl ExternalFiles for RootDatabase {}
 impl salsa::ParallelDatabase for RootDatabase {
     fn snapshot(&self) -> salsa::Snapshot<RootDatabase> {
         salsa::Snapshot::new(RootDatabase { storage: self.storage.snapshot() })
diff --git a/crates/cairo-lang-compiler/src/diagnostics.rs b/crates/cairo-lang-compiler/src/diagnostics.rs
index c7cc45ec203..ca16afabdca 100644
--- a/crates/cairo-lang-compiler/src/diagnostics.rs
+++ b/crates/cairo-lang-compiler/src/diagnostics.rs
@@ -130,6 +130,7 @@ impl<'a> DiagnosticsReporter<'a> {
                         ))
                     }
                     FileLongId::Virtual(_) => panic!("Missing virtual file."),
+                    FileLongId::External(_) => panic!("Missing external file."),
                 }
                 found_diagnostics = true;
             }
diff --git a/crates/cairo-lang-defs/src/test.rs b/crates/cairo-lang-defs/src/test.rs
index e27f4671673..09ad4be70b4 100644
--- a/crates/cairo-lang-defs/src/test.rs
+++ b/crates/cairo-lang-defs/src/test.rs
@@ -3,7 +3,8 @@ use std::sync::Arc;
 
 use cairo_lang_debug::debug::DebugWithDb;
 use cairo_lang_filesystem::db::{
-    init_files_group, AsFilesGroupMut, CrateConfiguration, FilesDatabase, FilesGroup, FilesGroupEx,
+    init_files_group, AsFilesGroupMut, CrateConfiguration, ExternalFiles, FilesDatabase,
+    FilesGroup, FilesGroupEx,
 };
 use cairo_lang_filesystem::ids::{CrateLongId, Directory, FileLongId};
 use cairo_lang_parser::db::{ParserDatabase, ParserGroup};
@@ -30,6 +31,7 @@ pub struct DatabaseForTesting {
     storage: salsa::Storage<DatabaseForTesting>,
 }
 impl salsa::Database for DatabaseForTesting {}
+impl ExternalFiles for DatabaseForTesting {}
 impl Default for DatabaseForTesting {
     fn default() -> Self {
         let mut res = Self { storage: Default::default() };
diff --git a/crates/cairo-lang-filesystem/src/db.rs b/crates/cairo-lang-filesystem/src/db.rs
index 08b9eede342..ea602884124 100644
--- a/crates/cairo-lang-filesystem/src/db.rs
+++ b/crates/cairo-lang-filesystem/src/db.rs
@@ -107,9 +107,27 @@ pub struct ExperimentalFeaturesConfig {
     pub coupons: bool,
 }
 
+/// A trait for defining files external to the `filesystem` crate.
+pub trait ExternalFiles {
+    /// Returns the content of an external file.
+    fn ext_file_content(&self, _external_id: u32) -> Option<Arc<str>> {
+        None
+    }
+
+    /// Returns the name of an external file.
+    fn ext_file_name(&self, _external_id: u32) -> String {
+        "<external>".to_string()
+    }
+
+    /// Returns the full path of an external file.
+    fn ext_file_full_path(&self, _external_id: u32) -> String {
+        "<external>".to_string()
+    }
+}
+
 // Salsa database interface.
 #[salsa::query_group(FilesDatabase)]
-pub trait FilesGroup {
+pub trait FilesGroup: ExternalFiles {
     #[salsa::interned]
     fn intern_crate(&self, crt: CrateLongId) -> CrateId;
     #[salsa::interned]
@@ -244,6 +262,7 @@ fn priv_raw_file_content(db: &dyn FilesGroup, file: FileId) -> Option<Arc<str>>
             Err(_) => None,
         },
         FileLongId::Virtual(virt) => Some(virt.content),
+        FileLongId::External(external_id) => db.ext_file_content(external_id),
     }
 }
 fn file_content(db: &dyn FilesGroup, file: FileId) -> Option<Arc<str>> {
diff --git a/crates/cairo-lang-filesystem/src/ids.rs b/crates/cairo-lang-filesystem/src/ids.rs
index 8426b0a45ad..746099c59d3 100644
--- a/crates/cairo-lang-filesystem/src/ids.rs
+++ b/crates/cairo-lang-filesystem/src/ids.rs
@@ -62,6 +62,7 @@ impl FlagId {
 pub enum FileLongId {
     OnDisk(PathBuf),
     Virtual(VirtualFile),
+    External(u32),
 }
 /// Whether the file holds syntax for a module or for an expression.
 #[derive(Clone, Debug, Hash, PartialEq, Eq)]
@@ -131,18 +132,21 @@ impl<'b> FileId {
                 path.file_name().and_then(|x| x.to_str()).unwrap_or("<unknown>").to_string()
             }
             FileLongId::Virtual(vf) => vf.name.to_string(),
+            FileLongId::External(external_id) => db.ext_file_name(external_id),
         }
     }
     pub fn full_path(self, db: &dyn FilesGroup) -> String {
         match self.lookup_intern(db) {
             FileLongId::OnDisk(path) => path.to_str().unwrap_or("<unknown>").to_string(),
             FileLongId::Virtual(vf) => vf.full_path(db),
+            FileLongId::External(external_id) => db.ext_file_full_path(external_id),
         }
     }
     pub fn kind(self, db: &dyn FilesGroup) -> FileKind {
         match self.lookup_intern(db) {
             FileLongId::OnDisk(_) => FileKind::Module,
             FileLongId::Virtual(vf) => vf.kind.clone(),
+            FileLongId::External(_) => FileKind::Module,
         }
     }
 }
diff --git a/crates/cairo-lang-filesystem/src/test_utils.rs b/crates/cairo-lang-filesystem/src/test_utils.rs
index ca1eb9792ab..5b01bbdcdab 100644
--- a/crates/cairo-lang-filesystem/src/test_utils.rs
+++ b/crates/cairo-lang-filesystem/src/test_utils.rs
@@ -1,6 +1,6 @@
 use cairo_lang_utils::Upcast;
 
-use crate::db::{init_files_group, AsFilesGroupMut, FilesDatabase, FilesGroup};
+use crate::db::{init_files_group, AsFilesGroupMut, ExternalFiles, FilesDatabase, FilesGroup};
 
 // Test salsa database.
 #[salsa::database(FilesDatabase)]
@@ -8,6 +8,7 @@ pub struct FilesDatabaseForTesting {
     storage: salsa::Storage<FilesDatabaseForTesting>,
 }
 impl salsa::Database for FilesDatabaseForTesting {}
+impl ExternalFiles for FilesDatabaseForTesting {}
 impl Default for FilesDatabaseForTesting {
     fn default() -> Self {
         let mut res = Self { storage: Default::default() };
diff --git a/crates/cairo-lang-formatter/src/test.rs b/crates/cairo-lang-formatter/src/test.rs
index 4e96a679952..b8f598dc3f9 100644
--- a/crates/cairo-lang-formatter/src/test.rs
+++ b/crates/cairo-lang-formatter/src/test.rs
@@ -1,7 +1,7 @@
 use std::fs;
 use std::path::PathBuf;
 
-use cairo_lang_filesystem::db::{FilesDatabase, FilesGroup};
+use cairo_lang_filesystem::db::{ExternalFiles, FilesDatabase, FilesGroup};
 use cairo_lang_parser::utils::{get_syntax_root_and_diagnostics_from_file, SimpleParserDatabase};
 use cairo_lang_syntax::node::db::SyntaxDatabase;
 use cairo_lang_utils::Upcast;
@@ -16,6 +16,7 @@ pub struct DatabaseImpl {
     storage: salsa::Storage<DatabaseImpl>,
 }
 impl salsa::Database for DatabaseImpl {}
+impl ExternalFiles for DatabaseImpl {}
 impl Upcast<dyn FilesGroup> for DatabaseImpl {
     fn upcast(&self) -> &(dyn FilesGroup + 'static) {
         self
diff --git a/crates/cairo-lang-language-server/src/lang/db/mod.rs b/crates/cairo-lang-language-server/src/lang/db/mod.rs
index 3412bdd4ba8..9fafd1c010a 100644
--- a/crates/cairo-lang-language-server/src/lang/db/mod.rs
+++ b/crates/cairo-lang-language-server/src/lang/db/mod.rs
@@ -1,7 +1,9 @@
 use cairo_lang_defs::db::{DefsDatabase, DefsGroup};
 use cairo_lang_doc::db::DocDatabase;
 use cairo_lang_filesystem::cfg::{Cfg, CfgSet};
-use cairo_lang_filesystem::db::{init_files_group, AsFilesGroupMut, FilesDatabase, FilesGroup};
+use cairo_lang_filesystem::db::{
+    init_files_group, AsFilesGroupMut, ExternalFiles, FilesDatabase, FilesGroup,
+};
 use cairo_lang_lowering::db::{init_lowering_group, LoweringDatabase, LoweringGroup};
 use cairo_lang_lowering::utils::InliningStrategy;
 use cairo_lang_parser::db::{ParserDatabase, ParserGroup};
@@ -71,6 +73,7 @@ impl AnalysisDatabase {
 }
 
 impl salsa::Database for AnalysisDatabase {}
+impl ExternalFiles for AnalysisDatabase {}
 
 impl salsa::ParallelDatabase for AnalysisDatabase {
     fn snapshot(&self) -> salsa::Snapshot<Self> {
diff --git a/crates/cairo-lang-language-server/src/lang/lsp/ls_proto_group.rs b/crates/cairo-lang-language-server/src/lang/lsp/ls_proto_group.rs
index f35fe27d837..7d56d5d1fd0 100644
--- a/crates/cairo-lang-language-server/src/lang/lsp/ls_proto_group.rs
+++ b/crates/cairo-lang-language-server/src/lang/lsp/ls_proto_group.rs
@@ -52,6 +52,9 @@ pub trait LsProtoGroup: Upcast<dyn FilesGroup> {
                 url.path_segments_mut().unwrap().push(&format!("{}.cairo", virtual_file.name));
                 url
             }
+            FileLongId::External(id) => {
+                unimplemented!("External files are not supported yet: {id}")
+            }
         }
     }
 }
diff --git a/crates/cairo-lang-lowering/src/test_utils.rs b/crates/cairo-lang-lowering/src/test_utils.rs
index 316f614b28e..bcdccb36385 100644
--- a/crates/cairo-lang-lowering/src/test_utils.rs
+++ b/crates/cairo-lang-lowering/src/test_utils.rs
@@ -2,7 +2,7 @@ use std::sync::{LazyLock, Mutex};
 
 use cairo_lang_defs::db::{DefsDatabase, DefsGroup};
 use cairo_lang_filesystem::db::{
-    init_dev_corelib, init_files_group, AsFilesGroupMut, FilesDatabase, FilesGroup,
+    init_dev_corelib, init_files_group, AsFilesGroupMut, ExternalFiles, FilesDatabase, FilesGroup,
 };
 use cairo_lang_filesystem::detect::detect_corelib;
 use cairo_lang_parser::db::{ParserDatabase, ParserGroup};
@@ -26,6 +26,7 @@ pub struct LoweringDatabaseForTesting {
     storage: salsa::Storage<LoweringDatabaseForTesting>,
 }
 impl salsa::Database for LoweringDatabaseForTesting {}
+impl ExternalFiles for LoweringDatabaseForTesting {}
 impl salsa::ParallelDatabase for LoweringDatabaseForTesting {
     fn snapshot(&self) -> salsa::Snapshot<LoweringDatabaseForTesting> {
         salsa::Snapshot::new(LoweringDatabaseForTesting { storage: self.storage.snapshot() })
diff --git a/crates/cairo-lang-parser/src/utils.rs b/crates/cairo-lang-parser/src/utils.rs
index 522d0905f95..1c054c620e8 100644
--- a/crates/cairo-lang-parser/src/utils.rs
+++ b/crates/cairo-lang-parser/src/utils.rs
@@ -1,7 +1,7 @@
 use std::path::PathBuf;
 
 use cairo_lang_diagnostics::{Diagnostics, DiagnosticsBuilder};
-use cairo_lang_filesystem::db::{init_files_group, FilesDatabase, FilesGroup};
+use cairo_lang_filesystem::db::{init_files_group, ExternalFiles, FilesDatabase, FilesGroup};
 use cairo_lang_filesystem::ids::{FileId, FileKind, FileLongId, VirtualFile};
 use cairo_lang_syntax::node::ast::SyntaxFile;
 use cairo_lang_syntax::node::db::{SyntaxDatabase, SyntaxGroup};
@@ -18,6 +18,7 @@ pub struct SimpleParserDatabase {
     storage: salsa::Storage<SimpleParserDatabase>,
 }
 impl salsa::Database for SimpleParserDatabase {}
+impl ExternalFiles for SimpleParserDatabase {}
 impl Default for SimpleParserDatabase {
     fn default() -> Self {
         let mut res = Self { storage: Default::default() };
diff --git a/crates/cairo-lang-plugins/src/test.rs b/crates/cairo-lang-plugins/src/test.rs
index fb85546eeca..85d7ff2a261 100644
--- a/crates/cairo-lang-plugins/src/test.rs
+++ b/crates/cairo-lang-plugins/src/test.rs
@@ -7,7 +7,8 @@ use cairo_lang_defs::plugin::{
 };
 use cairo_lang_filesystem::cfg::CfgSet;
 use cairo_lang_filesystem::db::{
-    init_files_group, AsFilesGroupMut, CrateConfiguration, FilesDatabase, FilesGroup, FilesGroupEx,
+    init_files_group, AsFilesGroupMut, CrateConfiguration, ExternalFiles, FilesDatabase,
+    FilesGroup, FilesGroupEx,
 };
 use cairo_lang_filesystem::ids::{CrateLongId, Directory, FileLongId};
 use cairo_lang_parser::db::ParserDatabase;
@@ -49,6 +50,7 @@ pub struct DatabaseForTesting {
     storage: salsa::Storage<DatabaseForTesting>,
 }
 impl salsa::Database for DatabaseForTesting {}
+impl ExternalFiles for DatabaseForTesting {}
 impl Default for DatabaseForTesting {
     fn default() -> Self {
         let mut res = Self { storage: Default::default() };
diff --git a/crates/cairo-lang-semantic/src/db.rs b/crates/cairo-lang-semantic/src/db.rs
index 48dd38bedf9..04744d4543a 100644
--- a/crates/cairo-lang-semantic/src/db.rs
+++ b/crates/cairo-lang-semantic/src/db.rs
@@ -1627,7 +1627,9 @@ fn module_semantic_diagnostics(
 
                         let path = match file_id.lookup_intern(db) {
                             FileLongId::OnDisk(path) => path.display().to_string(),
-                            FileLongId::Virtual(_) => panic!("Expected OnDisk file."),
+                            FileLongId::Virtual(_) | FileLongId::External(_) => {
+                                panic!("Expected OnDisk file.")
+                            }
                         };
 
                         let stable_location =
diff --git a/crates/cairo-lang-semantic/src/test_utils.rs b/crates/cairo-lang-semantic/src/test_utils.rs
index 2baaa01e52a..1a7cf997713 100644
--- a/crates/cairo-lang-semantic/src/test_utils.rs
+++ b/crates/cairo-lang-semantic/src/test_utils.rs
@@ -6,7 +6,7 @@ use cairo_lang_defs::ids::{FunctionWithBodyId, ModuleId, SubmoduleId, SubmoduleL
 use cairo_lang_diagnostics::{Diagnostics, DiagnosticsBuilder};
 use cairo_lang_filesystem::db::{
     init_dev_corelib, init_files_group, AsFilesGroupMut, CrateConfiguration, CrateSettings,
-    Edition, ExperimentalFeaturesConfig, FilesDatabase, FilesGroup,
+    Edition, ExperimentalFeaturesConfig, ExternalFiles, FilesDatabase, FilesGroup,
 };
 use cairo_lang_filesystem::detect::detect_corelib;
 use cairo_lang_filesystem::ids::{
@@ -30,6 +30,7 @@ pub struct SemanticDatabaseForTesting {
     storage: salsa::Storage<SemanticDatabaseForTesting>,
 }
 impl salsa::Database for SemanticDatabaseForTesting {}
+impl ExternalFiles for SemanticDatabaseForTesting {}
 impl salsa::ParallelDatabase for SemanticDatabaseForTesting {
     fn snapshot(&self) -> salsa::Snapshot<SemanticDatabaseForTesting> {
         salsa::Snapshot::new(SemanticDatabaseForTesting { storage: self.storage.snapshot() })
diff --git a/crates/cairo-lang-sierra-generator/src/test_utils.rs b/crates/cairo-lang-sierra-generator/src/test_utils.rs
index 96024f05363..2fb0b989610 100644
--- a/crates/cairo-lang-sierra-generator/src/test_utils.rs
+++ b/crates/cairo-lang-sierra-generator/src/test_utils.rs
@@ -3,7 +3,8 @@ use std::sync::{Arc, LazyLock, Mutex};
 use cairo_lang_defs::db::{DefsDatabase, DefsGroup};
 use cairo_lang_defs::ids::ModuleId;
 use cairo_lang_filesystem::db::{
-    init_dev_corelib, init_files_group, AsFilesGroupMut, FilesDatabase, FilesGroup, FilesGroupEx,
+    init_dev_corelib, init_files_group, AsFilesGroupMut, ExternalFiles, FilesDatabase, FilesGroup,
+    FilesGroupEx,
 };
 use cairo_lang_filesystem::detect::detect_corelib;
 use cairo_lang_filesystem::flag::Flag;
@@ -41,6 +42,7 @@ pub struct SierraGenDatabaseForTesting {
     storage: salsa::Storage<SierraGenDatabaseForTesting>,
 }
 impl salsa::Database for SierraGenDatabaseForTesting {}
+impl ExternalFiles for SierraGenDatabaseForTesting {}
 impl salsa::ParallelDatabase for SierraGenDatabaseForTesting {
     fn snapshot(&self) -> salsa::Snapshot<SierraGenDatabaseForTesting> {
         salsa::Snapshot::new(SierraGenDatabaseForTesting { storage: self.storage.snapshot() })
diff --git a/crates/cairo-lang-syntax/src/node/test_utils.rs b/crates/cairo-lang-syntax/src/node/test_utils.rs
index fb75a881cc0..3a5ee3bc289 100644
--- a/crates/cairo-lang-syntax/src/node/test_utils.rs
+++ b/crates/cairo-lang-syntax/src/node/test_utils.rs
@@ -1,4 +1,4 @@
-use cairo_lang_filesystem::db::{FilesDatabase, FilesGroup};
+use cairo_lang_filesystem::db::{ExternalFiles, FilesDatabase, FilesGroup};
 use cairo_lang_utils::Upcast;
 
 use super::db::SyntaxDatabase;
@@ -9,6 +9,7 @@ pub struct DatabaseForTesting {
     storage: salsa::Storage<DatabaseForTesting>,
 }
 impl salsa::Database for DatabaseForTesting {}
+impl ExternalFiles for DatabaseForTesting {}
 impl Upcast<dyn FilesGroup> for DatabaseForTesting {
     fn upcast(&self) -> &(dyn FilesGroup + 'static) {
         self