diff --git a/css/components/elements/_misc-content.scss b/css/components/elements/_misc-content.scss
index 7a43c8bcbb..83265a4cfc 100644
--- a/css/components/elements/_misc-content.scss
+++ b/css/components/elements/_misc-content.scss
@@ -151,6 +151,16 @@ article.theorem-like .emphasis {
     font-style: oblique;
 }
 
+.preview-build-warning {
+  background-color: rgb(249, 240, 240);
+  border: 2px solid rgb(202, 38, 38);
+  border-radius: 2px;
+  color: #333;
+  padding: 10px;
+  margin: 10px 0;
+}
+
+
 /* Adapted from William Hammond (attributed to David Carlisle) */
 /* "mathjax-users" Google Group, 2015-12-27 */
 
diff --git a/pretext/lib/pretext.py b/pretext/lib/pretext.py
index 502de99caa..4ed42ae502 100644
--- a/pretext/lib/pretext.py
+++ b/pretext/lib/pretext.py
@@ -91,6 +91,8 @@
 # contextmanager tools
 import contextlib
 
+import time
+
 # cleanup multiline strings used as source code
 import textwrap
 
@@ -4253,6 +4255,12 @@ def _parse_runestone_services(et):
 
     return (rs_js, rs_css, rs_cdn_url, rs_version)
 
+# Update stringparams with Runestone Services information
+def _set_runestone_stringparams(stringparams, rs_js, rs_css, rs_version):
+    stringparams["rs-js"] = rs_js
+    stringparams["rs-css"] = rs_css
+    stringparams["rs-version"] = rs_version
+
 # A helper function to query the latest Runestone
 # Services file, while failing gracefully
 
@@ -4298,15 +4306,8 @@ def _runestone_services(stringparams, ext_rs_methods):
     # Developer is responsible for placement of the right files in _static
     # ** Simply return early with stock values (or None) **
     if "debug.rs.dev" in stringparams:
-        rs_js = "prefix-runtime.bundle.js:prefix-runtime-libs.bundle.js:prefix-runestone.bundle.js"
-        rs_css = "prefix-runtime-libs.css:prefix-runestone.css"
-        rs_cdn_url = None
-        rs_version = "dev"
-        services_xml = None
-        # Return, plus side-effect
-        stringparams["rs-js"] = rs_js
-        stringparams["rs-css"] = rs_css
-        stringparams["rs-version"] = rs_version
+        rs_js, rs_css, rs_cdn_url, rs_version, services_xml = _runestone_debug_service_info()
+        _set_runestone_stringparams(stringparams, rs_js, rs_css, rs_version)
         return (rs_js, rs_css, rs_cdn_url, rs_version, services_xml)
 
     # Otherwise, we have a URL pointing to the Runestone server/CDN
@@ -4333,11 +4334,17 @@ def _runestone_services(stringparams, ext_rs_methods):
     rs_js, rs_css, rs_cdn_url, rs_version = _parse_runestone_services(services)
 
     # Return, plus side-effect
-    stringparams["rs-js"] = rs_js
-    stringparams["rs-css"] = rs_css
-    stringparams["rs-version"] = rs_version
+    _set_runestone_stringparams(stringparams, rs_js, rs_css, rs_version)
     return (rs_js, rs_css, rs_cdn_url, rs_version, services_xml)
 
+def _runestone_debug_service_info():
+    """Return hardcoded values used for debugging Runestone Services (debug.rs.dev)"""
+    rs_js = "prefix-runtime.bundle.js:prefix-runtime-libs.bundle.js:prefix-runestone.bundle.js"
+    rs_css = "prefix-runtime-libs.css:prefix-runestone.css"
+    rs_cdn_url = None
+    rs_version = "dev"
+    services_xml = None
+    return (rs_js, rs_css, rs_cdn_url, rs_version, services_xml)
 
 def _cdn_runestone_services(stringparams, ext_rs_methods):
     """Version of _runestone_services function to query the Runestone Services file from the PreTeXt html-static CDN"""
@@ -4442,6 +4449,21 @@ def query_runestone_services(services_url):
     return services_response.text
 
 
+def query_existing_runestone_services(dest_dir, stringparams):
+    '''Attempt to get Runestone service data from existing
+       Runestone Services file in _static directory.
+       Returns a tuple of the JS, CSS, CDN URL and version or None'''
+    services_record_files = os.path.join(dest_dir, "_static", "_runestone-services.xml")
+    
+    if os.path.exists(services_record_files):
+        with open(services_record_files, 'r') as f:
+            services_xml = f.read()
+        services = ET.fromstring(services_xml)
+        return _parse_runestone_services(services)
+    else:
+        msg = "query_existing_runestone_services failed: no _runestone-services.xml file found in _static directory"
+        raise RuntimeError(msg)
+
 def _place_runestone_services(tmp_dir, stringparams, ext_rs_methods):
     '''Obtain Runestone Services and place in _static directory of build'''
 
@@ -4715,6 +4737,9 @@ def html(xml, pub_file, stringparams, xmlid_root, file_format, extra_xsl, out_fi
     # to ensure provided stringparams aren't mutated unintentionally
     stringparams = stringparams.copy()
 
+    log_time_info = stringparams.get("profile-py", False) == "yes"
+    time_logger = Stopwatch("html()", log_time_info)
+
     # Consult publisher file for locations of images
     generated_abs, external_abs = get_managed_directories(xml, pub_file)
     # Consult source for additional files
@@ -4725,6 +4750,7 @@ def html(xml, pub_file, stringparams, xmlid_root, file_format, extra_xsl, out_fi
 
     pub_vars = get_publisher_variable_report(xml, pub_file, stringparams)
     include_static_files = get_publisher_variable(pub_vars, 'portable-html') != "yes"
+    time_logger.log("pubvars loaded")
 
     if include_static_files:
         # interrogate Runestone server (or debugging switches) and populate
@@ -4734,6 +4760,7 @@ def html(xml, pub_file, stringparams, xmlid_root, file_format, extra_xsl, out_fi
         # even if we don't need static files, we need to set stringparams for
         # Runestone Services information.
         _cdn_runestone_services(stringparams, ext_rs_methods)
+    time_logger.log("runestone placed")
 
     # support publisher file, and subtree argument
     if pub_file:
@@ -4752,18 +4779,19 @@ def html(xml, pub_file, stringparams, xmlid_root, file_format, extra_xsl, out_fi
     # place managed directories - some of these (Asymptote HTML) are
     # consulted during the XSL run and so need to be placed beforehand
     copy_managed_directories(tmp_dir, external_abs=external_abs, generated_abs=generated_abs, data_abs=data_dir)
+    time_logger.log("managed directories copied")
 
     if include_static_files:
         # Copy js and css, but only if not building portable html
         # place JS in scratch directory
         copy_html_js(tmp_dir)
-
-        # build or copy theme
         build_or_copy_theme(xml, pub_vars, tmp_dir)
+        time_logger.log("css/js copied")
 
     # Write output into temporary directory
     log.info("converting {} to HTML in {}".format(xml, tmp_dir))
     xsltproc(extraction_xslt, xml, None, tmp_dir, stringparams)
+    time_logger.log("xsltproc complete")
 
     if not(include_static_files):
         # remove latex-image generated directories for portable builds
@@ -4799,6 +4827,43 @@ def html(xml, pub_file, stringparams, xmlid_root, file_format, extra_xsl, out_fi
     else:
         raise ValueError("PTX:BUG: HTML file format not recognized")
 
+    time_logger.log("build completed")
+
+
+def html_incremental(xml, pub_file, stringparams, xmlid_root, extra_xsl, dest_dir):
+    """Update an HTML incrementally in place.
+       Depends on _static and generated files already being in the destination directory.
+       Caller must supply:
+       * stringparams supplemented with:
+          * rs-js, rs-css, and rs-version (can use _set_runestone_stringparams to set)
+          * publisher: path to publisher file for use by xsltproc
+    """
+    if not "rs-js" in stringparams:
+        log.error("Incremental build missing needed stringparam(s).  Unable to complete build.")
+        return False
+
+    # to ensure provided stringparams aren't mutated unintentionally
+    stringparams = stringparams.copy()
+
+    log_time_info = stringparams.get("profile-py", False) == "yes"
+    time_logger = Stopwatch("html_incremental()", log_time_info)
+
+    # support publisher file, and subtree argument
+    if pub_file:
+        stringparams["publisher"] = pub_file
+    if xmlid_root:
+        stringparams["subtree"] = xmlid_root
+
+    # Optional extra XSL could be None, or sanitized full filename
+    if extra_xsl:
+        extraction_xslt = extra_xsl
+    else:
+        extraction_xslt = os.path.join(get_ptx_xsl_path(), "pretext-html.xsl")
+
+    log.info("incremental convertsion of {} to HTML in {}".format(xml, dest_dir))
+    xsltproc(extraction_xslt, xml, None, dest_dir, stringparams)
+    time_logger.log("xsltproc complete")
+
 
 def revealjs(
     xml, pub_file, stringparams, xmlid_root, file_format, extra_xsl, out_file, dest_dir
@@ -6113,6 +6178,29 @@ def place_latex_package_files(dest_dir, journal_name, cache_dir):
         shutil.copy2(file_path, dest_dir)
 
 
+class Stopwatch:
+    """A simple stopwatch class for measuring elapsed time.    """
+    """print_log set to false disables logging of elapsed time """
+
+    def __init__(self, name:str="", print_log:bool=True):
+        self.name = name
+        self.print_log = print_log
+        self.start_time = time.time()
+        self.last_log_time = self.start_time
+    
+    def reset(self):
+        """Reset the log timer to the current time."""
+        self.last_log_time = time.time()
+
+    def log(self, timepoint_description:str=""):
+        """Print a log message with the elapsed time since the last log event."""
+        if self.print_log:
+            cur_time = time.time()
+            elapsed_time = cur_time - self.start_time
+            since_last_log_time = cur_time - self.last_log_time
+            self.reset()
+            log.info(f"** Timing report from {self.name}: {timepoint_description}, {since_last_log_time:.2f}s since last watch reset. {elapsed_time:.2f}s total elapsed time.")
+
 
 ###########################
 #
diff --git a/pretext/pretext b/pretext/pretext
index 0ad04e4cca..55335a690a 100755
--- a/pretext/pretext
+++ b/pretext/pretext
@@ -782,6 +782,37 @@ def main():
                 dest_dir,
                 None
             )
+        elif args.format == "html-incremental":
+            # -----------------------------------------
+            # Setup - this work could be done one time in a frontend that is monitoring changes
+            # Force incremental build flag
+            stringparams["html.build-incremental"] = "yes"
+            
+            log_time_info = stringparams.get("profile-py", False) == "yes"
+            time_logger = ptx.Stopwatch("pretext:html-incremental", log_time_info)
+
+            # attempt to reuse RS services
+            if "debug.rs.dev" in stringparams:
+                rs_js, rs_css, rs_cdn_url, rs_version, services_xml = ptx._runestone_debug_service_info()
+            else:
+                rs_js, rs_css, rs_cdn_url, rs_version = ptx.query_existing_runestone_services(
+                    dest_dir=dest_dir,
+                    stringparams=stringparams
+                )
+            ptx._set_runestone_stringparams(stringparams, rs_js, rs_css, rs_version)
+            time_logger.log("runestone stringparams set")
+
+            # -----------------------------------------
+            # Actual incremental build, this is the only work done on each change
+            ptx.html_incremental(
+                xml=xml_source,
+                pub_file=publication_file,
+                stringparams=stringparams,
+                xmlid_root=args.xmlid,
+                extra_xsl=extra_stylesheet,
+                dest_dir=dest_dir,
+            )
+            time_logger.log("complete incremental build")
         elif args.format == "html-zip":
             # no "subtree root" build is possible
             ptx.html(
diff --git a/xsl/pretext-assembly.xsl b/xsl/pretext-assembly.xsl
index bb2f9d1583..46d8422d17 100644
--- a/xsl/pretext-assembly.xsl
+++ b/xsl/pretext-assembly.xsl
@@ -348,6 +348,65 @@ along with PreTeXt.  If not, see <http://www.gnu.org/licenses/>.
     </xsl:copy>
 </xsl:template>
 
+<!-- Pruning templates generate a subtree towards $target-node    -->
+<!-- which prunes as many other branches as possible while        -->
+<!-- retaining reasonably decent output of the desire tree.       -->
+<!-- i.e. drop content other than titled structural elements.     -->
+<xsl:template match="@*" mode="pruning">
+    <xsl:apply-templates select="." mode="pruning-keep"/>
+</xsl:template>
+
+<xsl:template match="node()" mode="pruning">
+    <xsl:param name="target-node"/>
+    <xsl:choose>
+        <!-- This node contains the target node, copy and keep going -->
+        <xsl:when test="count(descendant::*|$target-node) = count(descendant::*)">
+            <xsl:copy>
+                <xsl:apply-templates select="node()|@*" mode="pruning">
+                    <xsl:with-param name="target-node" select="$target-node"/>
+                </xsl:apply-templates>
+            </xsl:copy>
+        </xsl:when>
+        <!-- This node is target node, keep it all -->
+        <xsl:when test="count(.|$target-node) = 1">
+            <xsl:apply-templates select="." mode="pruning-keep"/>
+        </xsl:when>
+        <!-- Shift to aggressive pruning -->
+        <xsl:otherwise>
+            <xsl:apply-templates select="." mode="pruning-prune"/>
+        </xsl:otherwise>
+    </xsl:choose>
+</xsl:template>
+
+<!-- Certain structural elements have data/metadata that we want to -->
+<!-- preserve, so we copy them over entirely.                       -->
+<xsl:template match="frontmatter|docinfo|bookinfo|backmatter" mode="pruning">
+    <xsl:copy>
+        <xsl:apply-templates select="node()|@*" mode="pruning-keep"/>
+    </xsl:copy>
+</xsl:template>
+
+<!-- Preserve anything from here on down -->
+<xsl:template match="node()|@*" mode="pruning-keep">
+    <xsl:copy>
+        <xsl:apply-templates select="node()|@*" mode="pruning-keep"/>
+    </xsl:copy>
+</xsl:template>
+
+<!-- Once aggressively pruning, only keep structural elements that give us -->
+<!-- numbering and toc info.                                               -->
+<xsl:template match="&STRUCTURAL;|@*" mode="pruning-prune">
+    <xsl:copy>
+        <xsl:apply-templates select="&STRUCTURAL;|title|@*" mode="pruning-prune">
+        </xsl:apply-templates>
+    </xsl:copy>
+</xsl:template>
+
+<!-- If we hit a title, grab all the contents so the ToC gets content-->
+<xsl:template match="title" mode="pruning-prune">
+    <xsl:apply-templates select="." mode="pruning-keep"/>
+</xsl:template>
+
 <!-- These templates initiate and create several iterations of -->
 <!-- the source tree via modal templates.  Think of each as a  -->
 <!-- "pass" through the source. Generally this constructs the  -->
@@ -414,12 +473,43 @@ along with PreTeXt.  If not, see <http://www.gnu.org/licenses/>.
 </xsl:variable>
 <xsl:variable name="original-labeled" select="exsl:node-set($original-labeled-rtf)"/>
 
+<!-- See pretext-html for full version of these params              -->
+<!-- "forward declared" here to avoid stylesheet ordering conflict  -->
+<xsl:param name="subtree" select="''"/>
+<xsl:param name="html.build-preview" select="''"/>
+<!-- After labeling, but before further processing, build a         -->
+<!-- pruned tree. Most of the time it is a copy of the labeled tree -->
+<!-- but when doing a preview build of a subtree, we prune          -->
+<!-- down the labeled tree to the desired subtree and select other  -->
+<!-- important elements.                                            -->
+<xsl:variable name="pruning-tree-rtf">
+    <xsl:choose>
+        <xsl:when test="$subtree != '' and $html.build-preview = 'yes'">
+            <xsl:variable name="target-node" select="$original-labeled//*[@xml:id = $subtree]"/>
+            <xsl:apply-templates select="$original-labeled" mode="pruning">
+                <xsl:with-param name="target-node" select="$original-labeled//*[@xml:id = $subtree]"/>
+            </xsl:apply-templates>
+        </xsl:when>
+        <xsl:otherwise>
+            <xsl:copy-of select="$original-labeled"/>
+        </xsl:otherwise>
+    </xsl:choose>
+</xsl:variable>
+<xsl:variable name="pruning-tree" select="exsl:node-set($pruning-tree-rtf)"/>
+
+<!-- Variable just to allow some printing after pruning-tree is established -->
+<xsl:variable name="not-used-pruning-info">
+    <xsl:if test="$subtree != '' and $html.build-preview = 'yes'">
+      <xsl:message>PTX:INFO: Pruned build tree to <xsl:value-of select="count($pruning-tree//node())"/> out of original <xsl:value-of select="count($original-labeled//node())"/> nodes.</xsl:message>
+    </xsl:if>
+</xsl:variable>
+
 <!-- A global list of all "webwork" used for       -->
 <!-- efficient backward-compatible indentification -->
-<xsl:variable name="all-webwork" select="$original-labeled//webwork"/>
+<xsl:variable name="all-webwork" select="$pruning-tree//webwork"/>
 
 <xsl:variable name="webwork-rtf">
-    <xsl:apply-templates select="$original-labeled" mode="webwork"/>
+    <xsl:apply-templates select="$pruning-tree" mode="webwork"/>
 </xsl:variable>
 <xsl:variable name="webworked" select="exsl:node-set($webwork-rtf)"/>
 
diff --git a/xsl/pretext-html.xsl b/xsl/pretext-html.xsl
index 5f0e1ae67f..ba32e47634 100644
--- a/xsl/pretext-html.xsl
+++ b/xsl/pretext-html.xsl
@@ -102,7 +102,22 @@ along with MathBook XML.  If not, see <http://www.gnu.org/licenses/>.
 <!-- Parameters -->
 <!-- Parameters to pass via xsltproc "stringparam" on command-line            -->
 <!-- Or make a thin customization layer and use 'select' to provide overrides -->
-<!-- See more generally applicable parameters in pretext-common.xsl file     -->
+<!-- See more generally applicable parameters in pretext-common.xsl file      -->
+
+<!-- Fast HTML builds that skip steps not needed for quickly rebuilding       -->
+<!-- individual pages in a document.                                          -->
+<!-- build-incremental: skips rebuilding search index, theme, Runestone       -->
+<!--   manifest, moving external/generated files,...                          -->
+<!--   Should produce clean diffs against pages from non-incremental build    -->
+<!-- build-preview, implies build-incremental and, when combined with         -->
+<!--   subtree, prunes the document to avoid processing nodes not part of     -->
+<!--   the output subtree.                                                    -->
+<!--   Will produce pages that are visually the same but have diffs when      -->
+<!--   compared to non-preview builds                                         -->
+<xsl:param name="html.build-preview" select="''"/>
+<xsl:variable name="b-build-preview" select="$html.build-preview = 'yes'"/>
+<xsl:param name="html.build-incremental" select="''"/>
+<xsl:variable name="b-build-incremental" select="$b-build-preview or $html.build-incremental = 'yes'"/>
 
 <!-- CSS and Javascript Directories -->
 <!-- These are convenience variables to specify file prefixes  -->
@@ -291,15 +306,27 @@ along with MathBook XML.  If not, see <http://www.gnu.org/licenses/>.
         </xsl:call-template>
     </xsl:if>
     <!--  -->
-    <xsl:apply-templates select="$original" mode="generic-warnings"/>
-    <xsl:apply-templates select="$original" mode="element-deprecation-warnings"/>
-    <xsl:apply-templates select="$original" mode="parameter-deprecation-warnings"/>
+    <xsl:choose>
+        <!-- If working on a subtree, only warn on that part.              -->
+        <!-- Not much speed difference, but helpful if author is focusing  -->
+        <!-- on a part of the work.                                        -->
+        <xsl:when test="$b-build-incremental and $b-subsetting">
+            <xsl:apply-templates select="$pruning-tree" mode="generic-warnings"/>
+            <xsl:apply-templates select="$pruning-tree" mode="element-deprecation-warnings"/>
+            <xsl:apply-templates select="$pruning-tree" mode="parameter-deprecation-warnings"/>
+        </xsl:when>
+        <xsl:otherwise>
+            <xsl:apply-templates select="$original" mode="generic-warnings"/>
+            <xsl:apply-templates select="$original" mode="element-deprecation-warnings"/>
+            <xsl:apply-templates select="$original" mode="parameter-deprecation-warnings"/>
+        </xsl:otherwise>
+    </xsl:choose>
     <!-- Usually no manifest is created -->
     <xsl:call-template name="runestone-manifest"/>
     <!-- A structured Table of Contents for a React app approach -->
     <xsl:call-template name="doc-manifest"/>
     <!-- build a search page (in development) -->
-    <xsl:if test="$has-native-search and not($b-portable-html)">
+    <xsl:if test="$has-native-search and not($b-build-incremental) and not($b-portable-html)">
         <xsl:call-template name="search-page-construction"/>
     </xsl:if>
     <!-- Optionally, build a SCORM manifest -->
@@ -11149,6 +11176,9 @@ along with MathBook XML.  If not, see <http://www.gnu.org/licenses/>.
                         </xsl:attribute>
                     </xsl:if>
                     <div id="ptx-content" class="ptx-content">
+                        <xsl:if test="$b-build-preview">
+                            <div class="preview-build-warning">Preview build. Links and knowls that cross pages may not function correctly.</div>
+                        </xsl:if>
                         <xsl:if test="$b-printable">
                             <div class="print-preview-header">
                                 <xsl:apply-templates select="." mode="print-preview-header"/>