diff --git a/ROADMAP.md b/ROADMAP.md
index c165e2a..c6d070a 100644
--- a/ROADMAP.md
+++ b/ROADMAP.md
@@ -87,6 +87,7 @@
 - [ ] don't use bullshit "sub-tokens", add filters and pipes as proper tokens.
 - [ ] Create a Location struct that somewhat matches Odin's [Source_Code_Location](https://pkg.odin-lang.org/base/runtime/#Source_Code_Location)?
   - Note that odin's version doesn't contain the stack trace.
+- [ ] Link checker / linter that warns if links don't resolve. ("please use {{whatever | rel_url }}").
 
 ### Memory Management
 
diff --git a/TODOS.md b/TODOS.md
index fe2ccd5..bb8be87 100644
--- a/TODOS.md
+++ b/TODOS.md
@@ -43,6 +43,9 @@ Remember to polish existing features before moving on to new ones.
       - do we want to do this or just use DIAGNOSTIC_TESTS.md as the tests?
       - [ ] also update to use file logger so they don't clog up the output
     - [ ] narrow highlight in diagnostic to relevent part of line.
+- [ ] page.url and page.permalink are confusing names. Switch to url + page_url
+  - There is confusion over how to do this and whethor or not `| rel_url` should be needed to render these.
+    Requires **careful thought**.
 
 ## Documentation
 
diff --git a/defaults/layouts/home.html b/defaults/layouts/home.html
index 56961ce..5fb7b70 100644
--- a/defaults/layouts/home.html
+++ b/defaults/layouts/home.html
@@ -5,7 +5,7 @@
     {{&content}}
   </header>
   <ul>
-    {{#pages}} <li><a href="{{permalink}}">{{&title}}</a><span>{{#date}}<time
+    {{#pages}} <li><a href="{{permalink | rel_url}}">{{&title}}</a><span>{{#date}}<time
           datetime="{{date}}">{{date | format}}</time>{{/date}}</span>
     </li>
     {{/pages}}
diff --git a/defaults/layouts/partials/nav.html b/defaults/layouts/partials/nav.html
index 625642a..620d2b3 100644
--- a/defaults/layouts/partials/nav.html
+++ b/defaults/layouts/partials/nav.html
@@ -1,9 +1,9 @@
 <header>
   <nav>
     <ul>
-      <li><a href="/">{{> home-link}}</a></li>
+      <li><a href="{{site.base_path}}/">{{> home-link}}</a></li>
       {{#menus.main}}
-      <li><a href="{{url}}">{{name}}</a></li>
+      <li><a href="{{url | rel_url}}">{{name}}</a></li>
       {{/menus.main}}
     </ul>
   </nav>
diff --git a/defaults/layouts/partials/styles.html b/defaults/layouts/partials/styles.html
index 3f49921..d1dc912 100644
--- a/defaults/layouts/partials/styles.html
+++ b/defaults/layouts/partials/styles.html
@@ -220,4 +220,4 @@ label.margin-toggle:not(.sidenote-number) {
   }
 }
 </style>
-{{#params.stylesheets}}<link rel="stylesheet" href="{{.}}">{{/params.stylesheets}}
+{{#params.stylesheets}}<link rel="stylesheet" href="{{.|rel_url}}">{{/params.stylesheets}}
diff --git a/defaults/layouts/section_index.html b/defaults/layouts/section_index.html
index 1683eff..92ecf75 100644
--- a/defaults/layouts/section_index.html
+++ b/defaults/layouts/section_index.html
@@ -7,7 +7,7 @@
   <section>
     <h2>{{key}}</h2>
     <ul>
-      {{#items}} <li><a href="{{permalink}}">{{&title}}</a><span>{{#date}}<time
+      {{#items}} <li><a href="{{permalink | rel_url}}">{{&title}}</a><span>{{#date}}<time
             datetime="{{date}}">{{date | format}}</time>{{/date}}</span>
       </li>
       {{/items}}
diff --git a/mustache/TODOS.md b/mustache/TODOS.md
index cda6f1d..e716ac1 100644
--- a/mustache/TODOS.md
+++ b/mustache/TODOS.md
@@ -4,3 +4,4 @@
 - [ ] Simplify `trim_standalone_whitespace` — four temp arrays (`li_buf`, `ri_buf`, `left_done`, `right_done`) could potentially be reduced to two by merging the done-tracking into the index buffers using sentinel values (e.g. `-2` = already trimmed).
 - [ ] Adjacent standalone tags don't capture indent for the second tag (e.g. `  {{>a}}\n  {{>b}}` — `{{>b}}` gets `indent=""` because its left text was consumed by `{{>a}}`'s right-trim). Blocks recover via `deindent_blocks`, but partials/parents have no fallback.
 - [ ] lazy load partials ? (with mutex)
+- [ ] Support changing delimiters (Set Delimiter tag `{{=<% %>=}}`). Delimiters `{{`/`}}`/`{{{`/`}}}` are hardcoded in [tokenizer.odin](./tokenizer.odin); needs an `=` sigil case, mutable open/close delimiters threaded through `tokenize`, and wiring up `spec/specs/delimiters.json` in `spec_test.odin` (fixture present but not run).
diff --git a/mustache/pipes.odin b/mustache/pipes.odin
index 2aad0a8..e357af7 100644
--- a/mustache/pipes.odin
+++ b/mustache/pipes.odin
@@ -24,6 +24,7 @@ Pipe_Op :: enum {
 	Group_By,
 	First,
 	Last,
+	Rel_Url,
 }
 
 // Pipe op names are derived from the enum via reflection (lowercased).
@@ -60,10 +61,10 @@ pipe_op_candidates :: proc(allocator := context.temp_allocator) -> []string {
 }
 
 Pipe_Filter :: struct {
-	op:       string,
-	args:     [dynamic; MAX_PIPE_ARGS]string,
-	op_pos:   int,
-	end_pos:  int,
+	op:      string,
+	args:    [dynamic; MAX_PIPE_ARGS]string,
+	op_pos:  int,
+	end_pos: int,
 }
 
 Group :: struct {
@@ -345,10 +346,56 @@ apply_filter :: proc(
 	case .Last:
 		span := filter.end_pos - filter.op_pos
 		return take(value, filter.args[:], false, tmpl, filter.op_pos, span)
+	case .Rel_Url:
+		str, ok := reflect.as_string(value)
+		if !ok {
+			return value, Error_Body {
+				msg = "rel_url may only be used on strings",
+				pos = pos,
+				kind = .Data,
+			}
+		}
+		result := rel_url(str, ctx)
+		return any{new_clone(result, context.temp_allocator), typeid_of(string)}, nil
 	}
 	return {}, nil
 }
 
+// rel_url prefixes a root-relative path (e.g. "/faq/") with the site's
+// base_path so links resolve correctly under a subpath deployment. Values that
+// are already absolute — a scheme ("http://"), protocol-relative ("//"), an
+// in-page fragment ("#"), or a "mailto:" — are returned unchanged, which keeps
+// external menu and footer links intact. base_path is read from the context
+// stack the same way `format` reads date_format/timezone.
+rel_url :: proc(path: string, ctx: []any) -> string {
+	if path == "" {
+		return path
+	}
+	if strings.has_prefix(path, "http://") ||
+	   strings.has_prefix(path, "https://") ||
+	   strings.has_prefix(path, "//") ||
+	   strings.has_prefix(path, "#") ||
+	   strings.has_prefix(path, "mailto:") {
+		return path
+	}
+
+	base := ""
+	if raw := resolve_name("base_path", ctx); raw != nil {
+		if s, ok := reflect.as_string(raw); ok {
+			base = s
+		}
+	}
+	if base == "" {
+		return path
+	}
+
+	// Only prefix root-relative paths; leave document-relative ones alone.
+	if path[0] == '/' {
+		return fmt.tprintf("%s%s", base, path)
+	}
+	return path
+}
+
 apply_format :: proc(
 	iso: string,
 	args: []string,
@@ -386,7 +433,15 @@ apply_format :: proc(
 }
 
 // Groups preserve first-appearance order from the input list.
-apply_group_by :: proc(value: any, args: []string, pos: int, span: int) -> (result: any, err: Error) {
+apply_group_by :: proc(
+	value: any,
+	args: []string,
+	pos: int,
+	span: int,
+) -> (
+	result: any,
+	err: Error,
+) {
 	if len(args) != 1 {
 		hint := ""
 		if len(args) == 0 {
@@ -406,7 +461,12 @@ apply_group_by :: proc(value: any, args: []string, pos: int, span: int) -> (resu
 
 	elem_info, count, data := list_info(value)
 	if elem_info == nil {
-		return nil, Error_Body{msg = "group_by expects a list", pos = pos, span = span, kind = .Data}
+		return nil, Error_Body {
+			msg = "group_by expects a list",
+			pos = pos,
+			span = span,
+			kind = .Data,
+		}
 	}
 
 	groups := make([dynamic]Group, 0, 8, context.temp_allocator)
@@ -486,13 +546,13 @@ take :: proc(
 	n := 1
 	if !is_list && len(args) == 0 {
 		warning = Error_Body {
-			msg = "defaulting to n=1 for string",
-			pos = op_pos,
-			span = span,
-			kind = .Warning,
+			msg    = "defaulting to n=1 for string",
+			pos    = op_pos,
+			span   = span,
+			kind   = .Warning,
 			source = tmpl.source,
-			path = tmpl.path,
-			hint = "consider specifying n explicitly",
+			path   = tmpl.path,
+			hint   = "consider specifying n explicitly",
 		}
 	}
 	if len(args) > 0 {
@@ -525,13 +585,13 @@ take :: proc(
 		op_name := from_start ? "first" : "last"
 		alt_name := from_start ? "last" : "first"
 		warning = Error_Body {
-			msg = fmt.tprintf("%s %d is equivalent to %s %d", op_name, n, alt_name, 0 - n),
-			pos = op_pos,
-			span = span,
-			kind = .Warning,
+			msg    = fmt.tprintf("%s %d is equivalent to %s %d", op_name, n, alt_name, 0 - n),
+			pos    = op_pos,
+			span   = span,
+			kind   = .Warning,
 			source = tmpl.source,
-			path = tmpl.path,
-			hint = "consider using the clearer form",
+			path   = tmpl.path,
+			hint   = "consider using the clearer form",
 		}
 		from_start = !from_start
 		n = 0 - n
@@ -557,4 +617,3 @@ take :: proc(
 		return any{new_clone(str[start:end], context.temp_allocator), typeid_of(string)}, warning
 	}
 }
-
diff --git a/site.odin b/site.odin
index 5b03681..2d59964 100644
--- a/site.odin
+++ b/site.odin
@@ -17,6 +17,12 @@ Site_Context :: struct {
 	title:       string,
 	description: string,
 	base_url:    string,
+	// base_path is the path component of base_url, normalized to a leading slash
+	// with no trailing slash ("" for root-hosted sites). Templates prefix internal
+	// root-relative links with it (directly, or via the `rel_url` pipe) so that
+	// subpath deployments — e.g. project pages at https://user.github.io/proj —
+	// resolve correctly.
+	base_path:   string,
 	params:      json.Object,
 	og:          Open_Graph,
 	menus:       map[string][]Menu_Entry,
@@ -127,6 +133,7 @@ init_site :: proc(site: ^Site, flags: Flags) {
 	}
 
 	site_apply_cli_flags(site, flags)
+	site.base_path = site_base_path(site.base_url, site_allocator(site))
 	site.config_path = path
 
 	site.og = og_for_site(site)
@@ -213,6 +220,48 @@ site_apply_config :: proc(site: ^Site, config: Config_File, config_dir: string)
 	site.queries = expand_path(config.queries, site_allocator(site))
 }
 
+// site_base_path extracts the path component of base_url, normalized to a
+// leading slash with no trailing slash. Returns "" for root-hosted sites.
+//
+//   "https://ex.com/thor/" → "/thor"
+//   "https://ex.com/a/b"   → "/a/b"
+//   "https://ex.com"       → ""
+//   "http://localhost:8080/" → ""
+site_base_path :: proc(base_url: string, allocator := context.allocator) -> string {
+	url := base_url
+
+	// Strip scheme so the first '/' we find is the start of the path, not the
+	// "//" separating scheme and host.
+	if idx := strings.index(url, "://"); idx >= 0 {
+		url = url[idx + 3:]
+	}
+
+	// The path begins at the first '/' after the host.
+	slash := strings.index_byte(url, '/')
+	if slash < 0 {
+		return ""
+	}
+	path := url[slash:]
+
+	// Drop any query or fragment.
+	if idx := strings.index_byte(path, '?'); idx >= 0 {
+		path = path[:idx]
+	}
+	if idx := strings.index_byte(path, '#'); idx >= 0 {
+		path = path[:idx]
+	}
+
+	// Trim trailing slashes; a bare "/" normalizes to "".
+	for len(path) > 0 && path[len(path) - 1] == '/' {
+		path = path[:len(path) - 1]
+	}
+	if path == "" {
+		return ""
+	}
+
+	return strings.clone(path, allocator)
+}
+
 // expand_path replaces a leading ~/ with $HOME/.
 expand_path :: proc(path: string, allocator := context.allocator) -> string {
 	if len(path) >= 2 && path[0] == '~' && path[1] == '/' {
diff --git a/site/thor.json b/site/thor.json
index 6fcfe8e..a76320c 100644
--- a/site/thor.json
+++ b/site/thor.json
@@ -1,6 +1,7 @@
 {
   "date": {
-    "timezone": "America/New_York"
+    "timezone": "America/New_York",
+    "format": "January 2, 2006"
   },
   "markdown_extensions": {
     "footnotes": true