diff --git a/Project.toml b/Project.toml
index 010d9f9..0663ea5 100644
--- a/Project.toml
+++ b/Project.toml
@@ -5,9 +5,7 @@ version = "0.1.0-DEV"
 
 [deps]
 RegistryInstances = "2792f1a3-b283-48e8-9a74-f99dce5104f3"
-URIs = "5c2747f8-b7ea-4ff2-ba2e-563bfd36b1d4"
 
 [compat]
 RegistryInstances = "0.1"
-URIs = "1"
 julia = "1.10"
diff --git a/src/MethodURL.jl b/src/MethodURL.jl
index 89b8d8f..e3f7bc0 100644
--- a/src/MethodURL.jl
+++ b/src/MethodURL.jl
@@ -3,9 +3,10 @@
 
 module MethodURL
 
+using Base: PkgId, UUID, inbase
 using RegistryInstances: reachable_registries, registry_info
-using URIs: URI
-using Base: PkgId
+
+export url
 
 function repo_and_path_to_url(repo, version, path, line)
     repo = chopsuffix(repo, ".git")
@@ -13,11 +14,12 @@ function repo_and_path_to_url(repo, version, path, line)
     if startswith(repo, "https://github.com")
         return join([repo, "blob", "v" * version, path * "#L$line"], "/")
     else
-        error("failed to handle $repo")
+        error("Failed to construct URL for repository $repo.")
     end
 end
 
-function repos_package(uuid)
+# Find repository in reachable registries by looking up UUID
+function repos_package(uuid::UUID)
     repos = String[]
     for reg in reachable_registries()
         entry = get(reg, uuid, nothing)
@@ -29,26 +31,53 @@ function repos_package(uuid)
     return repos
 end
 
+# Return errors instead of `nothing`
+function _uuid(M::Module)
+    uuid = PkgId(M).uuid
+    isnothing(uuid) && error("Failed to find UUID of package $M.")
+    return uuid
+end
+
+# Return errors instead of `nothing`
+function _pkgdir(M::Module)
+    dir = pkgdir(M)
+    isnothing(dir) && error("Failed to find directory of package $M.")
+    return dir
+end
+
 # TODO: If package is devved use local path
 # TODO: If package is added by URL, use that
 function url(m::Method)
     M = parentmodule(m)
-    uuid = PkgId(M).uuid
+    file = String(m.file)
     line = m.line
 
-    pkg_splitpath = splitpath(pkgdir(M))
-    file_splitpath = splitpath(String(m.file))
-    while !isempty(pkg_splitpath) && first(pkg_splitpath) == first(file_splitpath)
-        popfirst!(pkg_splitpath)
-        popfirst!(file_splitpath)
-    end
-    local_dir = join(file_splitpath, "/")
-
-    v = string(pkgversion(M))
     urls = String[]
-    for repo in repos_package(uuid)
-        url = repo_and_path_to_url(repo, v, local_dir, line)
+    if inbase(M)
+        # adapted from https://github.com/JuliaLang/julia/blob/8f5b7ca12ad48c6d740e058312fc8cf2bbe67848/base/methodshow.jl#L382-L388
+        commit = Base.GIT_VERSION_INFO.commit
+        if isempty(commit)
+            url = "https://github.com/JuliaLang/julia/tree/v$VERSION/base/$file#L$line"
+        else
+            url = "https://github.com/JuliaLang/julia/tree/$commit/base/$file#L$line"
+        end
         push!(urls, url)
+    else
+        uuid = _uuid(M)
+        pkg_splitpath = splitpath(_pkgdir(M))
+        file_splitpath = splitpath(file)
+        while !isempty(pkg_splitpath) && first(pkg_splitpath) == first(file_splitpath)
+            popfirst!(pkg_splitpath)
+            popfirst!(file_splitpath)
+        end
+        local_dir = join(file_splitpath, "/")
+        # @info M file uuid _pkgdir(M) local_dir
+
+        v = string(pkgversion(M))
+        for repo in repos_package(uuid)
+            url = repo_and_path_to_url(repo, v, local_dir, line)
+            push!(urls, url)
+        end
     end
     return urls
 end
diff --git a/test/Project.toml b/test/Project.toml
index 5904861..16e03fe 100644
--- a/test/Project.toml
+++ b/test/Project.toml
@@ -1,6 +1,7 @@
 [deps]
 Aqua = "4c88cf16-eb10-579e-8560-4a9242c79595"
 ExplicitImports = "7d51a73a-1435-4ff3-83d9-f097790105c7"
+HTTP = "cd3eb016-35fb-5094-929b-558a96fad6f3"
 JET = "c3a54625-cd67-489e-a8e7-0a5a0ff4e31b"
 JuliaFormatter = "98e50ef6-434e-11e9-1051-2b60c6c9e899"
 Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"
diff --git a/test/runtests.jl b/test/runtests.jl
index 8059033..6ad8fa1 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -1,4 +1,5 @@
 using MethodURL
+
 using Test
 using JuliaFormatter: JuliaFormatter
 using Aqua: Aqua
@@ -12,6 +13,18 @@ using ExplicitImports:
     check_all_qualified_accesses_via_owners,
     check_all_qualified_accesses_are_public
 
+using HTTP: request
+
+function url_exists(url)
+    response = request("GET", url; status_exception=false, redirect=true, retry=true)
+    if 200 ≤ response.status < 400
+        return true
+    else
+        @warn "Failed to request URL" url response.status response
+        return false
+    end
+end
+
 @testset verbose = true "MethodURL.jl" begin
     @testset verbose = true "Linting" begin
         @testset "Code formatting (JuliaFormatter.jl)" begin
@@ -31,13 +44,44 @@ using ExplicitImports:
             @testset "Improper explicit imports" begin
                 @test isnothing(check_no_stale_explicit_imports(MethodURL))
                 @test isnothing(check_all_explicit_imports_via_owners(MethodURL))
-                @test isnothing(check_all_explicit_imports_are_public(MethodURL))
+                @test isnothing(
+                    check_all_explicit_imports_are_public(
+                        MethodURL; ignore=(:PkgId, :inbase)
+                    ),
+                )
             end
             @testset "Improper qualified accesses" begin
                 @test isnothing(check_all_qualified_accesses_via_owners(MethodURL))
                 @test isnothing(check_no_self_qualified_accesses(MethodURL))
-                @test isnothing(check_all_qualified_accesses_are_public(MethodURL))
+                @test isnothing(
+                    check_all_qualified_accesses_are_public(
+                        MethodURL; ignore=(:GIT_VERSION_INFO,)
+                    ),
+                )
             end
         end
     end
+    @testset verbose = true "URL" begin
+        @testset "Base" begin
+            m1 = @which sqrt(1.0)
+            u1 = first(@inferred url(m1))
+            # @test url_exists(u1)
+        end
+        # @testset "Stdlib" begin
+        #     m2 = @which @test true
+        #     u2 = first(@inferred url(m2))
+        #     # @test url_exists(u2)
+        # end
+        # @testset "Local" begin
+        #     _m = @which sqrt(1.0)
+        #     m3 = @which url(_m)
+        #     u3 = first(@inferred url(m3))
+        #     # @test url_exists(u3)
+        # end
+        @testset "External" begin
+            m4 = @which Aqua.test_all(MethodURL)
+            u4 = first(@inferred url(m4))
+            # @test url_exists(u4)
+        end
+    end
 end