diff --git a/index.php b/index.php
index 9e80f945..2f699390 100755
--- a/index.php
+++ b/index.php
@@ -341,6 +341,11 @@ function handlePEARError($error, $method = null) {
     $interface->assign('error', $error);
     $interface->assign('module', $module);
     header('HTTP/1.1 404 Not Found');
+    // If the module was Bib API ("api") but the rewrite rules could not parse the URL
+    // then we could provide a developer error string in JSON form. For now, bail out.
+    if ($module == 'api') {
+      exit();
+    }
     $interface->setTemplate('error.tpl');
     $interface->display('layout.tpl');
 
diff --git a/playwright/test/slow/api.spec.js b/playwright/test/slow/api.spec.js
index ab53149d..9605bba2 100644
--- a/playwright/test/slow/api.spec.js
+++ b/playwright/test/slow/api.spec.js
@@ -1,14 +1,188 @@
 const { test, expect } = require('@playwright/test');
 
 const test_cid = '002312286'; // "Kōkogaku zasshi" arbitrarily chosen
+const test_cid2 = '100673017'; // "Tests of a portable wood chipper..." also arbitrarily chosen
 const test_truncated_cid = '2312286'; // Truncated version
+const test_htid = 'mdp.39015048895836'; // One of the htids on test_cid
+const test_htid2 = 'umn.31951d03005375z'; // Another htid, this one corresponding test_cid2
+
 
 test('XML with full CID', async ({ page }) => {
   const response = await page.goto(`/Record/${test_cid}.xml`);
-  await expect(response.ok()).toBeTruthy();
+  expect(response.ok()).toBeTruthy();
+  expect(response.headers()["content-type"]).toContain('text/xml');
 });
 
 test('XML with truncated CID', async ({ page }) => {
   const response = await page.goto(`/Record/${test_truncated_cid}.xml`);
-  await expect(response.ok()).toBeTruthy();
-});
\ No newline at end of file
+  expect(response.ok()).toBeTruthy();
+  expect(response.headers()["content-type"]).toContain('text/xml');
+});
+
+test('XML with HTID', async ({ page }) => {
+  const response = await page.goto(`/MARCXML/${test_htid}`);
+  expect(response.status()).toBe(200);
+  expect(response.headers()["content-type"]).toContain('text/xml');
+});
+
+// See https://github.com/hathitrust/catalog/wiki/Volume-API
+//   for an explanation of these inscrutable "b/qf/qv.t", "b/t/Q" codes.
+// API JSON single-record responses are of the form
+// {records: {cid: {...}, items: [...]}
+// =========== single-id query, b/qf/qv.t endpoint
+
+test('Bib API b/qf/qv.t brief recordnumber', async ({ page }) => {
+  const response = await page.goto(`/api/volumes/brief/recordnumber/${test_cid}.json`);
+  expect(response.status()).toBe(200);
+  expect(response.headers()["content-type"]).toContain('application/json');
+  const body = await response.json();
+  expect(body.records).toHaveProperty(test_cid);
+  // No marc-xml property
+  expect(body.records[test_cid]).not.toHaveProperty("marc-xml");
+  expect(body.items.length).toBeGreaterThan(0);
+});
+
+test('Bib API b/qf/qv.t full recordnumber', async ({ page }) => {
+  const response = await page.goto(`/api/volumes/full/recordnumber/${test_cid}.json`);
+  expect(response.status()).toBe(200);
+  expect(response.headers()["content-type"]).toContain('application/json');
+  const body = await response.json();
+  expect(body.records).toHaveProperty(test_cid);
+  // Has marc-xml property
+  expect(body.records[test_cid]).toHaveProperty("marc-xml");
+  expect(body.items.length).toBeGreaterThan(0);
+});
+
+test('Bib API b/qf/qv.t brief htid', async ({ page }) => {
+  const response = await page.goto(`/api/volumes/brief/htid/${test_htid}.json`);
+  expect(response.status()).toBe(200);
+  expect(response.headers()["content-type"]).toContain('application/json');
+  const body = await response.json();
+  expect(body.records).toHaveProperty(test_cid);
+  // No marc-xml property
+  expect(body.records[test_cid]).not.toHaveProperty("marc-xml");
+  expect(body.items.length).toBeGreaterThan(0);
+});
+
+test('Bib API b/qf/qv.t full htid', async ({ page }) => {
+  const response = await page.goto(`/api/volumes/full/htid/${test_htid}.json`);
+  expect(response.status()).toBe(200);
+  expect(response.headers()["content-type"]).toContain('application/json');
+  const body = await response.json();
+  expect(body.records).toHaveProperty(test_cid);
+  // Has marc-xml property
+  expect(body.records[test_cid]).toHaveProperty("marc-xml");
+  expect(body.items.length).toBeGreaterThan(0);
+});
+
+// =========== single-id query, b/t/Q endpoint
+test('Bib API b/t/Q brief 1-htid', async ({ page }) => {
+  const response = await page.goto(`/api/volumes/brief/json/htid:${test_htid}`);
+  expect(response.status()).toBe(200);
+  expect(response.headers()["content-type"]).toContain('application/json');
+  const body = await response.json();
+  expect(body[`htid:${test_htid}`]).toHaveProperty('records');
+  expect(body[`htid:${test_htid}`]).toHaveProperty('items');
+  // Has no marc-xml property
+  expect(body[`htid:${test_htid}`].records[test_cid]).not.toHaveProperty("marc-xml");
+  expect(Object.keys(body)).toHaveLength(1);
+});
+
+// =========== multi-id query, b/t/Q endpoint
+test('Bib API b/t/Q brief 2-htid', async ({ page }) => {
+  const response = await page.goto(`/api/volumes/brief/json/htid:${test_htid}|htid:${test_htid2}`);
+  expect(response.status()).toBe(200);
+  expect(response.headers()["content-type"]).toContain('application/json');
+  const body = await response.json();
+  expect(body[`htid:${test_htid}`]).toHaveProperty('records');
+  expect(body[`htid:${test_htid}`]).toHaveProperty('items');
+  expect(body[`htid:${test_htid2}`]).toHaveProperty('records');
+  expect(body[`htid:${test_htid2}`]).toHaveProperty('items');
+  // Has no marc-xml property
+  expect(body[`htid:${test_htid}`].records[test_cid]).not.toHaveProperty("marc-xml");
+  expect(body[`htid:${test_htid2}`].records[test_cid2]).not.toHaveProperty("marc-xml");
+  expect(Object.keys(body)).toHaveLength(2);
+});
+
+// Inconsistencies and possible misfeatures
+// b/t/Q allows any value for brevity and defaults to "brief"
+// This is inconsistent with b/qf/qv.t which requires b to be in {brief,full}
+test('Bib API b/t/Q b? 200', async ({ page }) => {
+  const response = await page.goto(`/api/volumes/blah/json/htid:${test_htid}`);
+  expect(response.status()).toBe(200);
+});
+
+// Error conditions (rewrite side)
+// These will be caught by the rewrite rules and return 404
+// These tests time out with firefox but succeed with all others
+test('Bib API b/qf/qv.t b? 404', async ({ page, browserName }) => {
+  test.skip(browserName === 'firefox', 'times out with firefox for unknown reason');
+  const response = await page.goto(`/api/volumes/blah/htid/${test_htid}.json`);
+  expect(response.status()).toBe(404);
+});
+
+test('Bib API b/qf/qv.t t? 404', async ({ page, browserName }) => {
+  test.skip(browserName === 'firefox', 'times out with firefox for unknown reason');
+  const response = await page.goto(`/api/volumes/brief/htid/${test_htid}.blah`);
+  expect(response.status()).toBe(404);
+});
+
+test('Bib API b/t/Q t? 404', async ({ page, browserName }) => {
+  test.skip(browserName === 'firefox', 'times out with firefox for unknown reason');
+  const response = await page.goto(`/api/volumes/brief/blah/htid:${test_htid}`);
+  expect(response.status()).toBe(404);
+});
+
+// Error conditions (volumes.php side)
+// These will be caught by volumes.php and return 400
+test('Bib API b/qf/qv.t qf? 400', async ({ page }) => {
+  const response = await page.goto(`/api/volumes/brief/blah/${test_htid}.json`);
+  expect(response.status()).toBe(400);
+});
+
+test('Bib API b/t/Q qf? 400', async ({ page }) => {
+  const response = await page.goto(`/api/volumes/brief/json/blah:${test_htid}`);
+  expect(response.status()).toBe(400);
+});
+
+// Empty results
+test('Bib API b/qf/qv.t qv? 200', async ({ page }) => {
+  const response = await page.goto('/api/volumes/brief/htid/blah.json');
+  const body = await response.json();
+  expect(response.status()).toBe(200);
+  expect(response.headers()["content-type"]).toContain('application/json');
+  // Single-record results have a `records` hash because volumes.php
+  // returns JSON crafted to correctly represent it as `{}`.
+  // Multi-record results do not have the opportunity to do so, so they show up with
+  // the `records` as `[]`, see below.
+  expect(body.records).toStrictEqual({});
+  expect(body.items).toStrictEqual([]);
+});
+
+test('Bib API b/t/Q qv? 200', async ({ page }) => {
+  const response = await page.goto('/api/volumes/brief/json/htid:blah');
+  const body = await response.json();
+  expect(response.status()).toBe(200);
+  expect(response.headers()["content-type"]).toContain('application/json');
+  // Multi-records are keyed from outside, if you will, so the records are in an array
+  // instead of a hash (compare and contrast the preceding example).
+  // This may be considered buggy behavior.
+  expect(body['htid:blah'].records).toStrictEqual([]);
+  expect(body['htid:blah'].items).toStrictEqual([]);
+});
+
+// Endpoint variants with implied brevity "brief"
+test('Bib API t/Q htid', async ({ page }) => {
+  const response = await page.goto(`/api/volumes/json/htid:${test_htid}`);
+  expect(response.status()).toBe(200);
+  const body = await response.json();
+  expect(body[`htid:${test_htid}`]).toHaveProperty('records');
+  expect(body[`htid:${test_htid}`]).toHaveProperty('items');
+});
+
+test('Bib API qf/qv.t htid', async ({ page }) => {
+  const response = await page.goto(`/api/volumes/htid/${test_htid}.json`);
+  expect(response.status()).toBe(200);
+  const body = await response.json();
+  expect(body.items.length).toBeGreaterThan(0);
+});
diff --git a/static/api/volumes.php b/static/api/volumes.php
index defaf685..56dd407d 100644
--- a/static/api/volumes.php
+++ b/static/api/volumes.php
@@ -5,9 +5,13 @@
 // Bail immediately if there's no query
 
 // print_r($_REQUEST);
+
+// This may not be possible without a 404 from the current rewrite rules.
 if (!isset($_REQUEST['q']) || !preg_match('/\S/', $_REQUEST['q'])) {
-	header("HTTP/1.0 400 Malformed");
-	exit();
+  header("HTTP/1.0 400 Malformed");
+  header('Content-type: application/json; charset=UTF-8');
+  echo json_encode(['message' => 'missing or empty query']);
+  exit();
 }
 
 require_once 'PEAR.php';
@@ -81,7 +85,14 @@
   'rows' => 200
 );
 
-if ($_REQUEST['brevity'] == 'full') {
+// Set brevity to the default value of "brief" as brevity is not always
+// provided by the rewrite rules in .htaccess
+$brevity = 'brief';
+if (isset($_REQUEST['brevity']) && $_REQUEST['brevity'] == 'full') {
+  $brevity = 'full';
+}
+
+if ($brevity == 'full') {
   $commonargs['fl']  = $commonargs['fl']  . ',fullrecord';
 }
 
@@ -104,6 +115,7 @@
 class QObj
 {
   public $string;
+  public $brevity;
   private $_id;
   public $tspecs = array(); # Transformed specs
   public $qspecs = array(); # Query specs for solr
@@ -111,11 +123,12 @@ class QObj
   
   
   
-  function __construct($str) {
+  function __construct($str, $brevity) {
     global $validField;
     global $fieldmap;
     
     $this->string = $str;
+    $this->brevity = $brevity;
     
     $specs = explode(';', $str);
     foreach ($specs as $spec) {
@@ -127,7 +140,7 @@ function __construct($str) {
 
       if ($field == 'id') {
         $this->_id = $fv[1];
-	continue;
+        continue;
       }
       if (!isset($fv[1])) {
         continue;
@@ -266,7 +279,7 @@ function recordsStructure($docs) {
           $rinfo[$index . 's'] = array();
         }
       }
-      if ($_REQUEST['brevity'] == 'full') {
+      if ($this->brevity == 'full') {
         $rinfo['marc-xml'] = $doc['fullrecord'];
       }
       $records[$docid] = $rinfo;
@@ -294,7 +307,7 @@ function itemsStructure($docs) {
         $iinfo['itemURL'] = "https://babel.hathitrust.org/cgi/pt?id=" . $htid;
 
         $rc = isset($ht['rights']) ? $ht['rights'] : 'ic';
-	$rc = is_array($rc) ? $rc[0] : $rc;
+        $rc = is_array($rc) ? $rc[0] : $rc;
         $iinfo['rightsCode'] = $rc;
         $iinfo['lastUpdate'] = $ht['ingest'];
         $iinfo['enumcron'] = (isset($ht['enumcron']) && preg_match('/\S/', $ht['enumcron']))? $ht['enumcron'] : false;
@@ -317,7 +330,7 @@ function itemsStructure($docs) {
 
 
 foreach ($qstrings as $qstring) {
-  $nqo = new QObj($qstring);
+  $nqo = new QObj($qstring, $brevity);
   $solrQueryComponents = array_merge($solrQueryComponents, $nqo->qspecs);
   $qobjs[$qstring] = $nqo;
 }
@@ -331,7 +344,8 @@ function itemsStructure($docs) {
 if (!preg_match('/\S/', $q)) {
   header('HTTP/1.1 400 Bad Request');
   $origQuery = htmlspecialchars($origQuery);
-  echo "Query '$origQuery' is invalid";
+  header('Content-type: application/json; charset=UTF-8');
+  echo json_encode(['message' => "query '$origQuery' is invalid"]);
   exit();
 }
 
@@ -387,12 +401,16 @@ function itemsStructure($docs) {
 
 if ($_REQUEST['type'] == 'json') {
   if (isset($allmatches['records']) && count($allmatches['records']) == 0) {
+    header('Content-type: application/json; charset=UTF-8');
+    // This is a hack to get the correct JSON representation of the empty `records` hash.
+    // Empty records can still show up serialized as "[]" in multi-record results.
+    // but this takes care of the simplest case.
     echo  "{\n \"records\": {}, \"items\": []\n}";
     exit;
   } else {
     $json = json_encode($allmatches);
     if (isset($_REQUEST['callback'])) {
-      header('Content-type: application/javascript; charset=UTF-8');  
+      header('Content-type: application/javascript; charset=UTF-8');
       echo $_REQUEST['callback'] . "( $json)";
     } else {
       header('Content-type: application/json; charset=UTF-8');