diff --git a/gems/instruments-ruby4.gemfile b/gems/instruments-ruby4.gemfile
index 6831864e..c616132b 100644
--- a/gems/instruments-ruby4.gemfile
+++ b/gems/instruments-ruby4.gemfile
@@ -10,4 +10,5 @@ gem 'moped'
 gem 'actionpack'
 gem 'actionview'
 gem 'httpx'
+gem 'webmock'
 gem 'grape'
diff --git a/gems/instruments.gemfile b/gems/instruments.gemfile
index 7e0124de..2c25febd 100644
--- a/gems/instruments.gemfile
+++ b/gems/instruments.gemfile
@@ -7,6 +7,7 @@ gem 'moped'
 gem 'actionpack'
 gem 'actionview'
 gem 'httpx'
+gem 'webmock'
 gem 'grape'
 # json 3.0 (released 2026-09) dropped the `quirks_mode` keyword that Grape 3's
 # ActiveSupport JSON formatter still passes, so any Grape 3 JSON request raises
diff --git a/gems/typhoeus.gemfile b/gems/typhoeus.gemfile
index 12dcfb9a..790a1e75 100644
--- a/gems/typhoeus.gemfile
+++ b/gems/typhoeus.gemfile
@@ -1,3 +1,4 @@
 eval_gemfile("../Gemfile")
 
 gem 'typhoeus'
+gem 'webmock'
diff --git a/test/unit/instruments/httpx_test.rb b/test/unit/instruments/httpx_test.rb
index ac48a023..dab38f93 100644
--- a/test/unit/instruments/httpx_test.rb
+++ b/test/unit/instruments/httpx_test.rb
@@ -4,17 +4,34 @@
   require 'scout_apm/instruments/httpx'
 
   require 'httpx'
+  require 'webmock'
 
   class HTTPXTest < Minitest::Test
+    include WebMock::API
+
     def setup
+      super # clears Thread.current[:scout_request] so a stale request from a
+            # prior test can't swallow this test's layers
+      WebMock.enable!
+      WebMock.disable_net_connect!
+
       @context = ScoutApm::AgentContext.new
       @recorder = FakeRecorder.new
       ScoutApm::Agent.instance.context.recorder = @recorder
       ScoutApm::Instruments::HTTPX.new(@context).install(prepend: false)
     end
 
+    def teardown
+      WebMock.reset!
+      WebMock.allow_net_connect!
+      WebMock.disable!
+      super
+    end
 
     def test_httpx
+      stub_request(:get, /news\.ycombinator\.com/).to_return(status: 200, body: "")
+      stub_request(:get, /google\.com/).to_return(status: 200, body: "")
+
       responses = HTTPX.get(
         "https://news.ycombinator.com/news",
         "https://news.ycombinator.com/news?p=2",
@@ -27,11 +44,18 @@ def test_httpx
     end
 
     def test_httpx_post_request
+      stub_request(:post, /httpbin\.org\/post/).to_return(status: 200, body: "")
+
       HTTPX.post("https://httpbin.org/post", json: { test: "data" })
       assert_recorded(@recorder, "HTTP", "POST", "httpbin.org/post")
     end
 
     def test_instruments_httpx_error_handling
+      # An error response still flows through Session#request, so the layer is
+      # started and stopped, and the request is recorded exactly once.
+      stub_request(:get, /thisshouldnotexistatall12345\.com/)
+        .to_return(status: 500, body: "")
+
       begin
         HTTPX.get("https://thisshouldnotexistatall12345.com")
       rescue
@@ -41,6 +65,10 @@ def test_instruments_httpx_error_handling
     end
 
     def test_httpx_request_retry
+      # A timed-out request is still dispatched through Session#request, so the
+      # layer is recorded even though the response errors.
+      stub_request(:get, /httpbin\.org\/delay/).to_timeout
+
       begin
         HTTPX.with(timeout: { connect_timeout: 0.25, request_timeout: 0.25 })
              .get("https://httpbin.org/delay/5")
@@ -50,14 +78,17 @@ def test_httpx_request_retry
     end
 
     def test_multiple_plugins
+      stub_request(:get, /news\.ycombinator\.com/).to_return(status: 200, body: "")
+      stub_request(:get, "http://httpbin.org/redirect/2")
+        .to_return(status: 302, headers: { "Location" => "http://httpbin.org/redirect/1" })
+      stub_request(:get, "http://httpbin.org/redirect/1")
+        .to_return(status: 302, headers: { "Location" => "http://httpbin.org/get" })
+      stub_request(:get, "http://httpbin.org/get").to_return(status: 200, body: "")
+
       session = HTTPX.plugin(:persistent).plugin(:follow_redirects)
 
       session.get("https://news.ycombinator.com/news")
-      begin
-        session.get("http://httpbin.org/redirect/2")
-      rescue
-        skip "httpbin.org not available"
-      end
+      session.get("http://httpbin.org/redirect/2")
 
       assert_equal 2, @recorder.requests.length, "Expected 2 requests to be recorded"
     end
diff --git a/test/unit/instruments/typhoeus_test.rb b/test/unit/instruments/typhoeus_test.rb
index bf59e05f..f5630c14 100644
--- a/test/unit/instruments/typhoeus_test.rb
+++ b/test/unit/instruments/typhoeus_test.rb
@@ -4,15 +4,31 @@
   require 'scout_apm/instruments/typhoeus'
 
   require 'typhoeus'
+  require 'webmock'
 
   class TyphoeusTest < Minitest::Test
+    include WebMock::API
+
     def setup
+      super # clears Thread.current[:scout_request] so a stale request from a
+            # prior test can't swallow this test's layers
+      WebMock.enable!
+      WebMock.disable_net_connect!
+      stub_request(:any, /example\.com/).to_return(status: 200, body: "")
+
       @context = ScoutApm::AgentContext.new
       @recorder = FakeRecorder.new
       ScoutApm::Agent.instance.context.recorder = @recorder
       ScoutApm::Instruments::Typhoeus.new(@context).install(prepend: false)
     end
 
+    def teardown
+      WebMock.reset!
+      WebMock.allow_net_connect!
+      WebMock.disable!
+      super
+    end
+
     def test_instruments_typhoeus_hydra
       hydra = Typhoeus::Hydra.new
       2.times.map{ hydra.queue(Typhoeus::Request.new("example.com", followlocation: true)) }
@@ -39,4 +55,4 @@ def assert_recorded(recorder, type, name, desc = nil)
       assert_equal desc, req.root_layer.desc if !desc.nil?
     end
   end
-end
\ No newline at end of file
+end