diff --git a/lib/docs/index.html b/lib/docs/index.html
index b10024a3e1..e60a3f960a 100644
--- a/lib/docs/index.html
+++ b/lib/docs/index.html
@@ -6,6 +6,9 @@
     <title>Zig Documentation</title>
     <link rel="icon" href="data:image/svg+xml;base64,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">
     <style type="text/css">
+      *, *::before, *::after {
+        box-sizing: border-box;
+      }
       body {
         font-family: system-ui, -apple-system, Roboto, "Segoe UI", sans-serif;
         color: #000000;
@@ -157,6 +160,23 @@
         cursor: default;
       }
 
+      #errors {
+        background-color: #faa;
+        position: fixed;
+        left: 0;
+        bottom: 0;
+        width: 100%;
+        max-height: min(20em, 50vh);
+        padding: 0.5em;
+        overflow: auto;
+      }
+      #errors h1 {
+        font-size: 1.5em;
+      }
+      #errors pre {
+        background-color: #fcc;
+      }
+
       #listSearchResults li.selected {
         background-color: #93e196;
       }
@@ -252,6 +272,14 @@
         #listSearchResults li.selected a {
           color: #fff;
         }
+        #errors {
+          background-color: #800;
+          color: #fff;
+        }
+        #errors pre {
+          background-color: #a00;
+          color: #fff;
+        }
         dl > div {
           border-color: #373737;
         }
@@ -414,6 +442,10 @@
       <dl><dt><kbd>↓</kbd></dt><dd>Move down in search results</dd></dl>
       <dl><dt><kbd>⏎</kbd></dt><dd>Go to active search result</dd></dl>
     </div>
+    <div id="errors" class="hidden">
+      <h1>Errors</h1>
+      <pre id="errorsText"></pre>
+    </div>
     <script src="main.js"></script>
   </body>
 </html>
diff --git a/lib/docs/main.js b/lib/docs/main.js
index 49c277b9f5..330b51ba49 100644
--- a/lib/docs/main.js
+++ b/lib/docs/main.js
@@ -11,6 +11,11 @@
     const CAT_type_type = 9;
     const CAT_type_function = 10;
 
+    const LOG_err = 0;
+    const LOG_warn = 1;
+    const LOG_info = 2;
+    const LOG_debug = 3;
+
     const domDocTestsCode = document.getElementById("docTestsCode");
     const domFnErrorsAnyError = document.getElementById("fnErrorsAnyError");
     const domFnProto = document.getElementById("fnProto");
@@ -48,6 +53,8 @@
     const domStatus = document.getElementById("status");
     const domTableFnErrors = document.getElementById("tableFnErrors");
     const domTldDocs = document.getElementById("tldDocs");
+    const domErrors = document.getElementById("errors");
+    const domErrorsText = document.getElementById("errorsText");
 
     var searchTimer = null;
 
@@ -84,13 +91,24 @@
 
     WebAssembly.instantiateStreaming(wasm_promise, {
       js: {
-        log: function(ptr, len) {
+        log: function(level, ptr, len) {
           const msg = decodeString(ptr, len);
-          console.log(msg);
-        },
-        panic: function (ptr, len) {
-            const msg = decodeString(ptr, len);
-            throw new Error("panic: " + msg);
+          switch (level) {
+            case LOG_err:
+              console.error(msg);
+              domErrorsText.textContent += msg + "\n";
+              domErrors.classList.remove("hidden");
+              break;
+            case LOG_warn:
+              console.warn(msg);
+              break;
+            case LOG_info:
+              console.info(msg);
+              break;
+            case LOG_debug:
+              console.debug(msg);
+              break;
+          }
         },
       },
     }).then(function(obj) {
diff --git a/lib/docs/wasm/Walk.zig b/lib/docs/wasm/Walk.zig
index 49a5e738fc..277cf88bef 100644
--- a/lib/docs/wasm/Walk.zig
+++ b/lib/docs/wasm/Walk.zig
@@ -406,15 +406,11 @@ pub const ModuleIndex = enum(u32) {
 };
 
 pub fn add_file(file_name: []const u8, bytes: []u8) !File.Index {
-    const ast = try parse(bytes);
+    const ast = try parse(file_name, bytes);
+    assert(ast.errors.len == 0);
     const file_index: File.Index = @enumFromInt(files.entries.len);
     try files.put(gpa, file_name, .{ .ast = ast });
 
-    if (ast.errors.len > 0) {
-        log.err("can't index '{s}' because it has syntax errors", .{file_index.path()});
-        return file_index;
-    }
-
     var w: Walk = .{
         .file = file_index,
     };
@@ -434,20 +430,41 @@ pub fn add_file(file_name: []const u8, bytes: []u8) !File.Index {
     return file_index;
 }
 
-fn parse(source: []u8) Oom!Ast {
+/// Parses a file and returns its `Ast`. If the file cannot be parsed, returns
+/// the `Ast` of an empty file, so that the rest of the Autodoc logic does not
+/// need to handle parse errors.
+fn parse(file_name: []const u8, source: []u8) Oom!Ast {
     // Require every source file to end with a newline so that Zig's tokenizer
     // can continue to require null termination and Autodoc implementation can
     // avoid copying source bytes from the decompressed tar file buffer.
     const adjusted_source: [:0]const u8 = s: {
         if (source.len == 0)
             break :s "";
-
-        assert(source[source.len - 1] == '\n');
+        if (source[source.len - 1] != '\n') {
+            log.err("{s}: expected newline at end of file", .{file_name});
+            break :s "";
+        }
         source[source.len - 1] = 0;
         break :s source[0 .. source.len - 1 :0];
     };
 
-    return Ast.parse(gpa, adjusted_source, .zig);
+    var ast = try Ast.parse(gpa, adjusted_source, .zig);
+    if (ast.errors.len > 0) {
+        defer ast.deinit(gpa);
+
+        const token_offsets = ast.tokens.items(.start);
+        var rendered_err: std.ArrayListUnmanaged(u8) = .{};
+        defer rendered_err.deinit(gpa);
+        for (ast.errors) |err| {
+            const err_offset = token_offsets[err.token] + ast.errorOffset(err);
+            const err_loc = std.zig.findLineColumn(ast.source, err_offset);
+            rendered_err.clearRetainingCapacity();
+            try ast.renderError(err, rendered_err.writer(gpa));
+            log.err("{s}:{}:{}: {s}", .{ file_name, err_loc.line + 1, err_loc.column + 1, rendered_err.items });
+        }
+        return Ast.parse(gpa, "", .zig);
+    }
+    return ast;
 }
 
 pub const Scope = struct {
diff --git a/lib/docs/wasm/main.zig b/lib/docs/wasm/main.zig
index 0ec2227512..91594e24b6 100644
--- a/lib/docs/wasm/main.zig
+++ b/lib/docs/wasm/main.zig
@@ -14,8 +14,15 @@ const missing_feature_url_escape = @import("html_render.zig").missing_feature_ur
 const gpa = std.heap.wasm_allocator;
 
 const js = struct {
-    extern "js" fn log(ptr: [*]const u8, len: usize) void;
-    extern "js" fn panic(ptr: [*]const u8, len: usize) noreturn;
+    /// Keep in sync with the `LOG_` constants in `main.js`.
+    const LogLevel = enum(u8) {
+        err,
+        warn,
+        info,
+        debug,
+    };
+
+    extern "js" fn log(level: LogLevel, ptr: [*]const u8, len: usize) void;
 };
 
 pub const std_options: std.Options = .{
@@ -36,14 +43,13 @@ fn logFn(
     comptime format: []const u8,
     args: anytype,
 ) void {
-    const level_txt = comptime message_level.asText();
-    const prefix2 = if (scope == .default) ": " else "(" ++ @tagName(scope) ++ "): ";
+    const prefix = if (scope == .default) "" else @tagName(scope) ++ ": ";
     var buf: [500]u8 = undefined;
-    const line = std.fmt.bufPrint(&buf, level_txt ++ prefix2 ++ format, args) catch l: {
+    const line = std.fmt.bufPrint(&buf, prefix ++ format, args) catch l: {
         buf[buf.len - 3 ..][0..3].* = "...".*;
         break :l &buf;
     };
-    js.log(line.ptr, line.len);
+    js.log(@field(js.LogLevel, @tagName(message_level)), line.ptr, line.len);
 }
 
 export fn alloc(n: usize) [*]u8 {
@@ -56,7 +62,7 @@ export fn unpack(tar_ptr: [*]u8, tar_len: usize) void {
     //log.debug("received {d} bytes of tar file", .{tar_bytes.len});
 
     unpackInner(tar_bytes) catch |err| {
-        fatal("unable to unpack tar: {s}", .{@errorName(err)});
+        std.debug.panic("unable to unpack tar: {s}", .{@errorName(err)});
     };
 }
 
@@ -514,7 +520,7 @@ export fn decl_fn_proto_html(decl_index: Decl.Index, linkify_fn_name: bool) Stri
         .collapse_whitespace = true,
         .fn_link = if (linkify_fn_name) decl_index else .none,
     }) catch |err| {
-        fatal("unable to render source: {s}", .{@errorName(err)});
+        std.debug.panic("unable to render source: {s}", .{@errorName(err)});
     };
     return String.init(string_result.items);
 }
@@ -524,7 +530,7 @@ export fn decl_source_html(decl_index: Decl.Index) String {
 
     string_result.clearRetainingCapacity();
     fileSourceHtml(decl.file, &string_result, decl.ast_node, .{}) catch |err| {
-        fatal("unable to render source: {s}", .{@errorName(err)});
+        std.debug.panic("unable to render source: {s}", .{@errorName(err)});
     };
     return String.init(string_result.items);
 }
@@ -536,7 +542,7 @@ export fn decl_doctest_html(decl_index: Decl.Index) String {
 
     string_result.clearRetainingCapacity();
     fileSourceHtml(decl.file, &string_result, doctest_ast_node, .{}) catch |err| {
-        fatal("unable to render source: {s}", .{@errorName(err)});
+        std.debug.panic("unable to render source: {s}", .{@errorName(err)});
     };
     return String.init(string_result.items);
 }
@@ -740,7 +746,7 @@ export fn decl_type_html(decl_index: Decl.Index) String {
                     .skip_comments = true,
                     .collapse_whitespace = true,
                 }) catch |e| {
-                    fatal("unable to render html: {s}", .{@errorName(e)});
+                    std.debug.panic("unable to render html: {s}", .{@errorName(e)});
                 };
                 string_result.appendSlice(gpa, "</code>") catch @panic("OOM");
                 break :t;
@@ -791,15 +797,6 @@ fn unpackInner(tar_bytes: []u8) !void {
     }
 }
 
-fn fatal(comptime format: []const u8, args: anytype) noreturn {
-    var buf: [500]u8 = undefined;
-    const line = std.fmt.bufPrint(&buf, format, args) catch l: {
-        buf[buf.len - 3 ..][0..3].* = "...".*;
-        break :l &buf;
-    };
-    js.panic(line.ptr, line.len);
-}
-
 fn ascii_lower(bytes: []u8) void {
     for (bytes) |*b| b.* = std.ascii.toLower(b.*);
 }