diff --git a/homepage/__init__.py b/homepage/__init__.py
index 1e7aad5..84438b5 100644
--- a/homepage/__init__.py
+++ b/homepage/__init__.py
@@ -1,6 +1,138 @@
+import os
+import re
+
 import check50
 
+
+# helper
+def html_pages():
+    return sorted(f for f in os.listdir(".") if f.endswith(".html"))
+
+
 @check50.check()
-def submitted():
-    """Homepage submitted"""
-   
\ No newline at end of file
+def required_files():
+    """required files exist"""
+    check50.exists("index.html")
+    check50.exists("styles.css")
+    check50.exists("specification.txt")
+
+
+@check50.check(required_files)
+def four_pages():
+    """contains at least 4 HTML pages including index.html"""
+    pages = html_pages()
+    if len(pages) < 4:
+        raise check50.Failure("expected at least 4 HTML pages")
+
+
+@check50.check(four_pages)
+def navigation():
+    """pages link to each other"""
+    pages = html_pages()
+    href_re = re.compile(r"""href\s*=\s*["']([^"']+)["']""", re.I)
+
+    for p in pages:
+        with open(p) as f:
+            html = f.read()
+        for m in href_re.finditer(html):
+            href = m.group(1).split("#", 1)[0].split("?", 1)[0]
+            if href in pages and href != p:
+                break
+        else:
+            raise check50.Failure("one or more pages do not link to another page")
+
+
+@check50.check(four_pages)
+def ten_distinct_tags():
+    """contains at least 10 distinct HTML tags besides html/head/body/title"""
+    tag_re = re.compile(r"<\s*([a-zA-Z][\w:-]*)\b")
+    used = set()
+
+    for p in html_pages():
+        with open(p) as f:
+            page = f.read()
+        for m in tag_re.finditer(page):
+            used.add(m.group(1).lower())
+    excluded_tags = {"html", "head", "body", "title"}
+    used -= excluded_tags
+    if len(used) < 10:
+        raise check50.Failure("fewer than 10 distinct HTML tags were found")
+
+
+@check50.check(four_pages)
+def bootstrap():
+    """Bootstrap is used"""
+    for p in html_pages():
+        with open(p) as f:
+            if "bootstrap" in f.read().lower():
+                return
+
+    raise check50.Failure(
+        "Bootstrap not detected",
+        help="Use Bootstrap on at least one page of your site."
+    )
+
+
+@check50.check(four_pages)
+def stylesheet():
+    """styles.css is linked"""
+    for p in html_pages():
+        with open(p) as f:
+            if "styles.css" in f.read().lower():
+                return
+
+    raise check50.Failure(
+        "styles.css not linked",
+        help="Link your own stylesheet (styles.css) from at least one page."
+    )
+
+
+@check50.check(four_pages)
+def css_rules():
+    """styles.css uses at least 5 selectors and 5 distinct properties"""
+    with open("styles.css") as f:
+        css = f.read()
+
+    # Count number of rule blocks
+    selector_count = css.count("{")
+
+    # Set of any "name:" occurrences
+    props_count = len(set(re.findall(r"([a-zA-Z-]+)\s*:", css)))
+
+    if selector_count < 5:
+        raise check50.Failure("styles.css does not appear to use at least 5 selectors")
+
+    if props_count < 5:
+        raise check50.Failure("styles.css does not appear to use at least 5 CSS properties")
+
+
+@check50.check(four_pages)
+def javascript():
+    """JavaScript is used"""
+    for p in html_pages():
+        with open(p) as f:
+            if "<script" in f.read().lower():
+                return
+
+    raise check50.Failure(
+        "no scripts detected",
+        help="Have you included some javascript via a script tag?"
+    )
+
+
+@check50.check(required_files)
+def specification():
+    """specification.txt contains required information"""
+    with open("specification.txt") as f:
+        spec = f.read().lower()
+
+    if "javascript" not in spec or "bootstrap" not in spec:
+        raise check50.Failure(
+            "specification.txt does not describe JavaScript and/or Bootstrap",
+            help="Have you included a one-sentence description of how you used JavaScript and Bootstrap?"
+        )
+    if len(spec.split()) < 25:
+        raise check50.Failure(
+            "specification.txt seems incomplete ",
+            help="Have you listed the 10 HTML tags and 5 CSS properties you’ve used?"
+        )