diff --git a/README.md b/README.md
index f47d1d0..f6384ad 100644
--- a/README.md
+++ b/README.md
@@ -38,7 +38,8 @@ Recent compromises in popular ecosystems:
 - [**telnyx 4.87.2**](https://safedep.io/malicious-telnyx-pypi-compromise/) - a legitimate telecom SDK hijacked on PyPI
 - [**pino-sdk-v2**](https://safedep.io/malicious-npm-package-pino-sdk-v2-env-exfiltration/) - a typosquat package disguised as the popular pino logger
 
-PMG intercepts every package install and checks it for malware **before** code executes. Install it once, and PMG covers every `npm install`, `pip install`, and `poetry add` after that.
+
+**PMG is free, open source (Apache 2.0), and requires no account or API key.** It intercepts every package install and checks it against [SafeDep's free community API](https://safedep.io) for known malware **before** code executes. Install it once, and it covers every `npm install`, `pip install`, and `poetry add` after that. 
 
 > Featured in [tl;dr sec](https://tldrsec.com/p/tldr-sec-316).
 
diff --git a/proxy/interceptors/pypi_cooldown.go b/proxy/interceptors/pypi_cooldown.go
index b960222..8ce0daa 100644
--- a/proxy/interceptors/pypi_cooldown.go
+++ b/proxy/interceptors/pypi_cooldown.go
@@ -4,6 +4,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"net/http"
+	"strings"
 	"time"
 
 	packagev1 "buf.build/gen/go/safedep/api/protocolbuffers/go/safedep/messages/package/v1"
@@ -26,9 +27,21 @@ func newPypiCooldownHandler(statsCollector *AnalysisStatsCollector) *pypiCooldow
 
 // HandleMetadataRequest overrides the Accept header to force a PEP 691 JSON response,
 // then registers a response modifier that strips files for versions within the cooldown window.
+// If the client does not support PEP 691 (pip < 22.3), cooldown is skipped to avoid
+// returning a content type the client cannot parse.
 func (h *pypiCooldownHandler) HandleMetadataRequest(ctx *proxy.RequestContext, packageName string, cooldownDays int, pinnedVersion string) (*proxy.InterceptorResponse, error) {
 	log.Debugf("[%s] Cooldown: registering metadata modifier for %s", ctx.RequestID, packageName)
 
+	originalAccept := ctx.Headers.Get("Accept")
+	clientSupportsPEP691 := strings.Contains(originalAccept, pypiSimpleAPIContentType)
+
+	if !clientSupportsPEP691 {
+		log.Warnf("[%s] Cooldown: client does not support PEP 691 JSON (Accept: %s), "+
+			"cooldown cannot be enforced for %s. Upgrade pip to 22.3+ for cooldown support.",
+			ctx.RequestID, originalAccept, packageName)
+		return &proxy.InterceptorResponse{Action: proxy.ActionAllow}, nil
+	}
+
 	// Force PEP 691 JSON so we receive upload-time per file entry.
 	ctx.Headers.Set("Accept", pypiSimpleAPIContentType)
 	// Prevent compression so the response body can be parsed as JSON directly.
diff --git a/proxy/interceptors/pypi_cooldown_test.go b/proxy/interceptors/pypi_cooldown_test.go
index 56a2938..301c48f 100644
--- a/proxy/interceptors/pypi_cooldown_test.go
+++ b/proxy/interceptors/pypi_cooldown_test.go
@@ -352,7 +352,7 @@ func TestStripCooldownFiles_UnparseableFilename_KeepFile(t *testing.T) {
 func TestPyPICooldown_HandleMetadataRequest_OverridesHeaders(t *testing.T) {
 	handler := newPypiCooldownHandler(nil)
 	ctx := makeTestRequestContext("https://pypi.org/simple/requests/")
-	ctx.Headers.Set("Accept", "text/html")
+	ctx.Headers.Set("Accept", "application/vnd.pypi.simple.v1+json, text/html;q=0.01")
 	ctx.Headers.Set("Accept-Encoding", "gzip")
 	ctx.Headers.Set("If-None-Match", `"abc123"`)
 	ctx.Headers.Set("If-Modified-Since", "Wed, 01 Jan 2025 00:00:00 GMT")
@@ -366,9 +366,22 @@ func TestPyPICooldown_HandleMetadataRequest_OverridesHeaders(t *testing.T) {
 	assert.Empty(t, ctx.Headers.Get("If-Modified-Since"))
 }
 
+func TestPyPICooldown_HandleMetadataRequest_ClientWithoutPEP691_SkipsCooldown(t *testing.T) {
+	handler := newPypiCooldownHandler(nil)
+	ctx := makeTestRequestContext("https://pypi.org/simple/requests/")
+	ctx.Headers.Set("Accept", "text/html")
+
+	resp, err := handler.HandleMetadataRequest(ctx, "requests", 5, "")
+	require.NoError(t, err)
+	assert.Equal(t, proxy.ActionAllow, resp.Action)
+	assert.Nil(t, resp.ResponseModifier)
+	assert.Equal(t, "text/html", ctx.Headers.Get("Accept"))
+}
+
 func TestPyPICooldown_HandleMetadataRequest_NonJSONResponse_FailOpen(t *testing.T) {
 	handler := newPypiCooldownHandler(nil)
 	ctx := makeTestRequestContext("https://pypi.org/simple/requests/")
+	ctx.Headers.Set("Accept", pypiSimpleAPIContentType)
 
 	resp, err := handler.HandleMetadataRequest(ctx, "requests", 5, "")
 	require.NoError(t, err)
@@ -395,6 +408,7 @@ func TestPyPICooldown_HandleMetadataRequest_StripsRecentVersions(t *testing.T) {
 
 	handler := newPypiCooldownHandler(NewAnalysisStatsCollector())
 	ctx := makeTestRequestContext("https://pypi.org/simple/testpkg/")
+	ctx.Headers.Set("Accept", pypiSimpleAPIContentType)
 
 	resp, err := handler.HandleMetadataRequest(ctx, "testpkg", 5, "")
 	require.NoError(t, err)
@@ -432,6 +446,7 @@ func TestPyPICooldown_HandleMetadataRequest_AllVersionsInCooldown_RecordsStats(t
 	collector := NewAnalysisStatsCollector()
 	handler := newPypiCooldownHandler(collector)
 	ctx := makeTestRequestContext("https://pypi.org/simple/newpkg/")
+	ctx.Headers.Set("Accept", pypiSimpleAPIContentType)
 
 	resp, err := handler.HandleMetadataRequest(ctx, "newpkg", 5, "")
 	require.NoError(t, err)
@@ -465,6 +480,7 @@ func TestPyPICooldown_HandleMetadataRequest_NoVersionsInCooldown_BodyUnchanged(t
 
 	handler := newPypiCooldownHandler(nil)
 	ctx := makeTestRequestContext("https://pypi.org/simple/testpkg/")
+	ctx.Headers.Set("Accept", pypiSimpleAPIContentType)
 
 	resp, err := handler.HandleMetadataRequest(ctx, "testpkg", 5, "")
 	require.NoError(t, err)
@@ -481,6 +497,7 @@ func TestPyPICooldown_HandleMetadataRequest_NoVersionsInCooldown_BodyUnchanged(t
 func TestPyPICooldown_HandleMetadataRequest_MalformedJSON_FailOpen(t *testing.T) {
 	handler := newPypiCooldownHandler(nil)
 	ctx := makeTestRequestContext("https://pypi.org/simple/badpkg/")
+	ctx.Headers.Set("Accept", pypiSimpleAPIContentType)
 
 	resp, err := handler.HandleMetadataRequest(ctx, "badpkg", 5, "")
 	require.NoError(t, err)
@@ -507,6 +524,7 @@ func TestPyPICooldown_HandleMetadataRequest_PinnedVersionInCooldown_RecordsStats
 	collector := NewAnalysisStatsCollector()
 	handler := newPypiCooldownHandler(collector)
 	ctx := makeTestRequestContext("https://pypi.org/simple/testpkg/")
+	ctx.Headers.Set("Accept", pypiSimpleAPIContentType)
 
 	resp, err := handler.HandleMetadataRequest(ctx, "testpkg", 5, "2.0.0")
 	require.NoError(t, err)
@@ -541,6 +559,7 @@ func TestPyPICooldown_HandleMetadataRequest_PinnedVersionNotInCooldown_NoBlock(t
 	collector := NewAnalysisStatsCollector()
 	handler := newPypiCooldownHandler(collector)
 	ctx := makeTestRequestContext("https://pypi.org/simple/testpkg/")
+	ctx.Headers.Set("Accept", pypiSimpleAPIContentType)
 
 	resp, err := handler.HandleMetadataRequest(ctx, "testpkg", 5, "1.0.0")
 	require.NoError(t, err)
@@ -568,6 +587,7 @@ func TestPyPICooldown_HandleMetadataRequest_UnpinnedWithRemainingVersions_NoBloc
 	collector := NewAnalysisStatsCollector()
 	handler := newPypiCooldownHandler(collector)
 	ctx := makeTestRequestContext("https://pypi.org/simple/testpkg/")
+	ctx.Headers.Set("Accept", pypiSimpleAPIContentType)
 
 	resp, err := handler.HandleMetadataRequest(ctx, "testpkg", 5, "")
 	require.NoError(t, err)
@@ -590,7 +610,7 @@ func TestPyPICooldown_InterceptorDelegation_CooldownEnabled(t *testing.T) {
 
 	ctx := makeTestRequestContext("https://pypi.org/simple/requests/")
 	ctx.Hostname = "pypi.org"
-	ctx.Headers.Set("Accept", "text/html")
+	ctx.Headers.Set("Accept", "application/vnd.pypi.simple.v1+json, text/html;q=0.01")
 
 	resp, err := interceptor.HandleRequest(ctx)
 	require.NoError(t, err)
@@ -598,6 +618,21 @@ func TestPyPICooldown_InterceptorDelegation_CooldownEnabled(t *testing.T) {
 	assert.Equal(t, "application/vnd.pypi.simple.v1+json", ctx.Headers.Get("Accept"))
 }
 
+func TestPyPICooldown_InterceptorDelegation_CooldownEnabled_OldPip(t *testing.T) {
+	setCooldownConfig(t, config.DependencyCooldownConfig{Enabled: true, Days: 5})
+
+	interceptor := NewPypiRegistryInterceptor(nil, NewInMemoryAnalysisCache(), NewAnalysisStatsCollector(), make(chan *ConfirmationRequest, 1), InterceptorContext{})
+
+	ctx := makeTestRequestContext("https://pypi.org/simple/requests/")
+	ctx.Hostname = "pypi.org"
+	ctx.Headers.Set("Accept", "text/html")
+
+	resp, err := interceptor.HandleRequest(ctx)
+	require.NoError(t, err)
+	assert.Equal(t, proxy.ActionAllow, resp.Action)
+	assert.Equal(t, "text/html", ctx.Headers.Get("Accept"))
+}
+
 func TestPyPICooldown_InterceptorDelegation_CooldownDisabled(t *testing.T) {
 	setCooldownConfig(t, config.DependencyCooldownConfig{Enabled: false, Days: 5})