diff --git a/jhttp/getter_test.go b/jhttp/getter_test.go
index 6046db8..98ceb7d 100644
--- a/jhttp/getter_test.go
+++ b/jhttp/getter_test.go
@@ -4,7 +4,6 @@ package jhttp_test
 
 import (
 	"context"
-	"encoding/hex"
 	"fmt"
 	"io"
 	"net/http"
@@ -17,6 +16,7 @@ import (
 	"github.com/creachadair/jrpc2/handler"
 	"github.com/creachadair/jrpc2/jhttp"
 	"github.com/fortytw2/leaktest"
+	"github.com/google/go-cmp/cmp"
 )
 
 func TestGetter(t *testing.T) {
@@ -70,6 +70,98 @@ func TestGetter(t *testing.T) {
 	})
 }
 
+func TestParseQuery(t *testing.T) {
+	tests := []struct {
+		url     string
+		body    string
+		method  string
+		want    interface{}
+		errText string
+	}{
+		// Error: Missing method name.
+		{"http://localhost:2112/", "", "", nil, "empty URL path"},
+
+		// No parameters.
+		{"http://localhost/foo", "", "foo", nil, ""},
+
+		// Unbalanced double-quoted string.
+		{"https://fuzz.ball/foo?bad=%22xyz", "", "foo", nil, "missing string quote"},
+		{"https://fuzz.ball/bar?bad=xyz%22", "", "bar", nil, "missing string quote"},
+
+		// Unbalanced single-quoted string.
+		{`http://stripe/sister?bad='invalid`, "", "sister", nil, "missing bytes quote"},
+		{`http://stripe/sister?bad=invalid'`, "", "sister", nil, "missing bytes quote"},
+
+		// Invalid byte string.
+		{`http://green.as/balls?bad='NOT%20VALID'`, "", "balls", nil, "decoding bytes"},
+
+		// Invalid double-quoted string.
+		{`http://black.as/sin?bad=%22a%5Cx25%22`, "", "sin", nil, "invalid character"},
+
+		// Valid: Single-quoted byte string (base64).
+		{`http://fast.as.hell/and?twice='YXMgcHJldHR5IGFzIHlvdQ=='`,
+			"", "and", map[string]interface{}{
+				"twice": []byte("as pretty as you"),
+			}, ""},
+
+		// Valid: Unquoted strings and null.
+		{`http://head.like/a-hole?black=as&your=null&soul`,
+			"", "a-hole", map[string]interface{}{
+				"black": "as",
+				"your":  nil,
+				"soul":  "",
+			}, ""},
+
+		// Valid: Quoted strings, numbers, Booleans.
+		{`http://foo.com:1999/go/west/?alpha=%22xyz%22&bravo=3&charlie=true&delta=false&echo=3.2`,
+			"", "go/west", map[string]interface{}{
+				"alpha":   "xyz",
+				"bravo":   int64(3),
+				"charlie": true,
+				"delta":   false,
+				"echo":    3.2,
+			}, ""},
+
+		// Valid: Form-encoded query in the request body.
+		{`http://buz.org:2013/bodyblow`,
+			"alpha=%22pdq%22&bravo=-19.4&charlie=false", "bodyblow", map[string]interface{}{
+				"alpha":   "pdq",
+				"bravo":   float64(-19.4),
+				"charlie": false,
+			}, ""},
+	}
+	for _, test := range tests {
+		t.Run("ParseQuery", func(t *testing.T) {
+			req, err := http.NewRequest("PUT", test.url, strings.NewReader(test.body))
+			if err != nil {
+				t.Fatalf("New request for %q failed: %v", test.url, err)
+			}
+			if test.body != "" {
+				req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
+			}
+
+			method, params, err := jhttp.ParseQuery(req)
+			if err != nil {
+				if test.errText == "" {
+					t.Fatalf("ParseQuery failed: %v", err)
+				} else if !strings.Contains(err.Error(), test.errText) {
+					t.Fatalf("ParseQuery: got error %v, want %q", err, test.errText)
+				}
+			} else if test.errText != "" {
+				t.Fatalf("ParseQuery: got method %q, params %+v, wanted error %q",
+					method, params, test.errText)
+			} else {
+				if method != test.method {
+					t.Errorf("ParseQuery method: got %q, want %q", method, test.method)
+				}
+				if diff := cmp.Diff(test.want, params); diff != "" {
+					t.Errorf("Wrong params: (-want, +got)\n%s", diff)
+				}
+			}
+		})
+	}
+}
+
 func TestGetter_parseRequest(t *testing.T) {
 	defer leaktest.Check(t)()
 
@@ -84,22 +176,15 @@ func TestGetter_parseRequest(t *testing.T) {
 			if err := req.ParseForm(); err != nil {
 				return "", nil, err
 			}
-			params := make(map[string]interface{})
-			for key := range req.Form {
-				val := req.Form.Get(key)
-				v, err := strconv.Atoi(val)
-				if err == nil {
-					params[key] = v
-					continue
-				}
-				b, err := hex.DecodeString(val)
-				if err == nil {
-					params[key] = b
-					continue
-				}
-				params[key] = val
+			tag := req.Form.Get("tag")
+			val, err := strconv.ParseInt(req.Form.Get("value"), 10, 64)
+			if err != nil && req.Form.Get("value") != "" {
+				return "", nil, fmt.Errorf("invalid number: %w", err)
 			}
-			return strings.TrimPrefix(req.URL.Path, "/x/"), params, nil
+			return strings.TrimPrefix(req.URL.Path, "/x/"), map[string]interface{}{
+				"tag":   tag,
+				"value": val,
+			}, nil
 		},
 	})
 	defer checkClose(t, g)
@@ -127,8 +212,8 @@ func TestGetter_parseRequest(t *testing.T) {
 	})
 	t.Run("InternalError", func(t *testing.T) {
 		// N.B. Parameter type does not match on the server side.
-		got := mustGet(t, url("x/format?tag=foo&value=bar"), http.StatusInternalServerError)
-		const want = `"code":-32602` // InvalidParams
+		got := mustGet(t, url("x/format?tag=foo&value=bar"), http.StatusBadRequest)
+		const want = `"code":-32700` // ParseError
 		if !strings.Contains(got, want) {
 			t.Errorf("Response body: got %#q, want %#q", got, want)
 		}