diff --git a/ql/lib/codeql/ruby/filters/GeneratedCode.qll b/ql/lib/codeql/ruby/filters/GeneratedCode.qll
new file mode 100644
index 00000000000..18d12be3aac
--- /dev/null
+++ b/ql/lib/codeql/ruby/filters/GeneratedCode.qll
@@ -0,0 +1,43 @@
+/** Provides classes for detecting generated code. */
+
+private import ruby
+private import codeql.ruby.ast.internal.TreeSitter
+
+/** A source file that contains generated code. */
+abstract class GeneratedCodeFile extends RubyFile { }
+
+/** A file contining comments suggesting it contains generated code. */
+class GeneratedCommentFile extends GeneratedCodeFile {
+  GeneratedCommentFile() { this = any(GeneratedCodeComment c).getLocation().getFile() }
+}
+
+/** A comment line that indicates generated code. */
+abstract class GeneratedCodeComment extends Ruby::Comment { }
+
+/**
+ * A generic comment line that suggests that the file is generated.
+ */
+class GenericGeneratedCodeComment extends GeneratedCodeComment {
+  GenericGeneratedCodeComment() {
+    exists(string line, string entity, string was, string automatically | line = getValue() |
+      entity = "file|class|art[ei]fact|module|script" and
+      was = "was|is|has been" and
+      automatically = "automatically |mechanically |auto[- ]?" and
+      line.regexpMatch("(?i).*\\bThis (" + entity + ") (" + was + ") (" + automatically +
+          ")?generated\\b.*")
+    )
+  }
+}
+
+/** A comment warning against modifications. */
+class DontModifyMarkerComment extends GeneratedCodeComment {
+  DontModifyMarkerComment() {
+    exists(string line | line = getValue() |
+      line.regexpMatch("(?i).*\\bGenerated by\\b.*\\bDo not edit\\b.*") or
+      line.regexpMatch("(?i).*\\bAny modifications to this file will be lost\\b.*")
+    )
+  }
+}
+
+/** Holds if `file` looks like it contains generated code. */
+predicate isGeneratedCode(GeneratedCodeFile file) { any() }
diff --git a/ql/src/AlertSuppression.ql b/ql/src/AlertSuppression.ql
new file mode 100644
index 00000000000..0ea3c64d747
--- /dev/null
+++ b/ql/src/AlertSuppression.ql
@@ -0,0 +1,82 @@
+/**
+ * @name Alert suppression
+ * @description Generates information about alert suppressions.
+ * @kind alert-suppression
+ * @id rb/alert-suppression
+ */
+
+import ruby
+import codeql.ruby.ast.internal.TreeSitter
+
+/**
+ * An alert suppression comment.
+ */
+class SuppressionComment extends Ruby::Comment {
+  string annotation;
+
+  SuppressionComment() {
+    // suppression comments must be single-line
+    this.getLocation().getStartLine() = this.getLocation().getEndLine() and
+    exists(string text | text = commentText(this) |
+      // match `lgtm[...]` anywhere in the comment
+      annotation = text.regexpFind("(?i)\\blgtm\\s*\\[[^\\]]*\\]", _, _)
+      or
+      // match `lgtm` at the start of the comment and after semicolon
+      annotation = text.regexpFind("(?i)(?<=^|;)\\s*lgtm(?!\\B|\\s*\\[)", _, _).trim()
+    )
+  }
+
+  /**
+   * Gets the text of this suppression comment.
+   */
+  string getText() { result = commentText(this) }
+
+  /** Gets the suppression annotation in this comment. */
+  string getAnnotation() { result = annotation }
+
+  /**
+   * Holds if this comment applies to the range from column `startcolumn` of line `startline`
+   * to column `endcolumn` of line `endline` in file `filepath`.
+   */
+  predicate covers(string filepath, int startline, int startcolumn, int endline, int endcolumn) {
+    this.getLocation().hasLocationInfo(filepath, startline, _, endline, endcolumn) and
+    startcolumn = 1
+  }
+
+  /** Gets the scope of this suppression. */
+  SuppressionScope getScope() { this = result.getSuppressionComment() }
+}
+
+private string commentText(Ruby::Comment comment) { result = comment.getValue().suffix(1) }
+
+/**
+ * The scope of an alert suppression comment.
+ */
+class SuppressionScope extends @ruby_token_comment {
+  SuppressionScope() { this instanceof SuppressionComment }
+
+  /** Gets a suppression comment with this scope. */
+  SuppressionComment getSuppressionComment() { result = this }
+
+  /**
+   * Holds if this element is at the specified location.
+   * The location spans column `startcolumn` of line `startline` to
+   * column `endcolumn` of line `endline` in file `filepath`.
+   * For more information, see
+   * [Locations](https://help.semmle.com/QL/learn-ql/ql/locations.html).
+   */
+  predicate hasLocationInfo(
+    string filepath, int startline, int startcolumn, int endline, int endcolumn
+  ) {
+    this.(SuppressionComment).covers(filepath, startline, startcolumn, endline, endcolumn)
+  }
+
+  /** Gets a textual representation of this element. */
+  string toString() { result = "suppression range" }
+}
+
+from SuppressionComment c
+select c, // suppression comment
+  c.getText(), // text of suppression comment (excluding delimiters)
+  c.getAnnotation(), // text of suppression annotation
+  c.getScope() // scope of suppression
diff --git a/ql/src/filters/ClassifyFiles.ql b/ql/src/filters/ClassifyFiles.ql
new file mode 100644
index 00000000000..d194523e09d
--- /dev/null
+++ b/ql/src/filters/ClassifyFiles.ql
@@ -0,0 +1,20 @@
+/**
+ * @name Classify files
+ * @description This query produces a list of all files in a database
+ *              that are classified as generated code or test code.
+ *
+ *              Used by LGTM.
+ * @kind file-classifier
+ * @id rb/file-classifier
+ */
+
+import ruby
+import codeql.ruby.filters.GeneratedCode
+
+predicate classify(File f, string category) {
+  f instanceof GeneratedCodeFile and category = "generated"
+}
+
+from File f, string category
+where classify(f, category)
+select f, category
diff --git a/ql/test/query-tests/AlertSuppression/.gitattributes b/ql/test/query-tests/AlertSuppression/.gitattributes
new file mode 100644
index 00000000000..7ed66a396cf
--- /dev/null
+++ b/ql/test/query-tests/AlertSuppression/.gitattributes
@@ -0,0 +1 @@
+TestWindows.java eol=crlf
diff --git a/ql/test/query-tests/AlertSuppression/AlertSuppression.expected b/ql/test/query-tests/AlertSuppression/AlertSuppression.expected
new file mode 100644
index 00000000000..840b13f61bc
--- /dev/null
+++ b/ql/test/query-tests/AlertSuppression/AlertSuppression.expected
@@ -0,0 +1,48 @@
+| Test.rb:1:16:1:21 | # lgtm |  lgtm | lgtm | Test.rb:1:1:1:21 | suppression range |
+| Test.rb:2:1:2:32 | # lgtm[rb/confusing-method-name] |  lgtm[rb/confusing-method-name] | lgtm[rb/confusing-method-name] | Test.rb:2:1:2:32 | suppression range |
+| Test.rb:3:1:3:65 | # lgtm[rb/confusing-method-name, rb/non-short-circuit-evaluation] |  lgtm[rb/confusing-method-name, rb/non-short-circuit-evaluation] | lgtm[rb/confusing-method-name, rb/non-short-circuit-evaluation] | Test.rb:3:1:3:65 | suppression range |
+| Test.rb:4:1:4:23 | # lgtm[@tag:exceptions] |  lgtm[@tag:exceptions] | lgtm[@tag:exceptions] | Test.rb:4:1:4:23 | suppression range |
+| Test.rb:5:1:5:48 | # lgtm[@tag:exceptions,rb/confusing-method-name] |  lgtm[@tag:exceptions,rb/confusing-method-name] | lgtm[@tag:exceptions,rb/confusing-method-name] | Test.rb:5:1:5:48 | suppression range |
+| Test.rb:6:1:6:27 | # lgtm[@expires:2017-06-11] |  lgtm[@expires:2017-06-11] | lgtm[@expires:2017-06-11] | Test.rb:6:1:6:27 | suppression range |
+| Test.rb:7:1:7:78 | # lgtm[rb/confusing-method-name] does not seem confusing despite alert by lgtm |  lgtm[rb/confusing-method-name] does not seem confusing despite alert by lgtm | lgtm[rb/confusing-method-name] | Test.rb:7:1:7:78 | suppression range |
+| Test.rb:8:1:8:17 | # lgtm: blah blah |  lgtm: blah blah | lgtm | Test.rb:8:1:8:17 | suppression range |
+| Test.rb:9:1:9:31 | # lgtm blah blah #falsepositive |  lgtm blah blah #falsepositive | lgtm | Test.rb:9:1:9:31 | suppression range |
+| Test.rb:10:1:10:33 | #lgtm  [rb/confusing-method-name] | lgtm  [rb/confusing-method-name] | lgtm  [rb/confusing-method-name] | Test.rb:10:1:10:33 | suppression range |
+| Test.rb:11:1:11:8 | # lgtm[] |  lgtm[] | lgtm[] | Test.rb:11:1:11:8 | suppression range |
+| Test.rb:13:1:13:5 | #lgtm | lgtm | lgtm | Test.rb:13:1:13:5 | suppression range |
+| Test.rb:14:1:14:6 | #\tlgtm | \tlgtm | lgtm | Test.rb:14:1:14:6 | suppression range |
+| Test.rb:15:1:15:33 | # lgtm\t[rb/confusing-method-name] |  lgtm\t[rb/confusing-method-name] | lgtm\t[rb/confusing-method-name] | Test.rb:15:1:15:33 | suppression range |
+| Test.rb:18:1:18:11 | # foo; lgtm |  foo; lgtm | lgtm | Test.rb:18:1:18:11 | suppression range |
+| Test.rb:19:1:19:37 | # foo; lgtm[rb/confusing-method-name] |  foo; lgtm[rb/confusing-method-name] | lgtm[rb/confusing-method-name] | Test.rb:19:1:19:37 | suppression range |
+| Test.rb:21:1:21:36 | # foo lgtm[rb/confusing-method-name] |  foo lgtm[rb/confusing-method-name] | lgtm[rb/confusing-method-name] | Test.rb:21:1:21:36 | suppression range |
+| Test.rb:23:1:23:40 | # foo lgtm[rb/confusing-method-name] bar |  foo lgtm[rb/confusing-method-name] bar | lgtm[rb/confusing-method-name] | Test.rb:23:1:23:40 | suppression range |
+| Test.rb:24:1:24:7 | # LGTM! |  LGTM! | LGTM | Test.rb:24:1:24:7 | suppression range |
+| Test.rb:25:1:25:32 | # LGTM[rb/confusing-method-name] |  LGTM[rb/confusing-method-name] | LGTM[rb/confusing-method-name] | Test.rb:25:1:25:32 | suppression range |
+| Test.rb:26:1:26:73 | #lgtm[rb/confusing-method-name] and lgtm[rb/non-short-circuit-evaluation] | lgtm[rb/confusing-method-name] and lgtm[rb/non-short-circuit-evaluation] | lgtm[rb/confusing-method-name] | Test.rb:26:1:26:73 | suppression range |
+| Test.rb:26:1:26:73 | #lgtm[rb/confusing-method-name] and lgtm[rb/non-short-circuit-evaluation] | lgtm[rb/confusing-method-name] and lgtm[rb/non-short-circuit-evaluation] | lgtm[rb/non-short-circuit-evaluation] | Test.rb:26:1:26:73 | suppression range |
+| Test.rb:27:1:27:37 | #lgtm[rb/confusing-method-name]; lgtm | lgtm[rb/confusing-method-name]; lgtm | lgtm | Test.rb:27:1:27:37 | suppression range |
+| Test.rb:27:1:27:37 | #lgtm[rb/confusing-method-name]; lgtm | lgtm[rb/confusing-method-name]; lgtm | lgtm[rb/confusing-method-name] | Test.rb:27:1:27:37 | suppression range |
+| TestWindows.rb:1:23:1:29 | # lgtm\r |  lgtm\r | lgtm | TestWindows.rb:1:1:1:29 | suppression range |
+| TestWindows.rb:2:1:2:33 | # lgtm[rb/confusing-method-name]\r |  lgtm[rb/confusing-method-name]\r | lgtm[rb/confusing-method-name] | TestWindows.rb:2:1:2:33 | suppression range |
+| TestWindows.rb:3:1:3:66 | # lgtm[rb/confusing-method-name, rb/non-short-circuit-evaluation]\r |  lgtm[rb/confusing-method-name, rb/non-short-circuit-evaluation]\r | lgtm[rb/confusing-method-name, rb/non-short-circuit-evaluation] | TestWindows.rb:3:1:3:66 | suppression range |
+| TestWindows.rb:4:1:4:24 | # lgtm[@tag:exceptions]\r |  lgtm[@tag:exceptions]\r | lgtm[@tag:exceptions] | TestWindows.rb:4:1:4:24 | suppression range |
+| TestWindows.rb:5:1:5:49 | # lgtm[@tag:exceptions,rb/confusing-method-name]\r |  lgtm[@tag:exceptions,rb/confusing-method-name]\r | lgtm[@tag:exceptions,rb/confusing-method-name] | TestWindows.rb:5:1:5:49 | suppression range |
+| TestWindows.rb:6:1:6:28 | # lgtm[@expires:2017-06-11]\r |  lgtm[@expires:2017-06-11]\r | lgtm[@expires:2017-06-11] | TestWindows.rb:6:1:6:28 | suppression range |
+| TestWindows.rb:7:1:7:79 | # lgtm[rb/confusing-method-name] does not seem confusing despite alert by lgtm\r |  lgtm[rb/confusing-method-name] does not seem confusing despite alert by lgtm\r | lgtm[rb/confusing-method-name] | TestWindows.rb:7:1:7:79 | suppression range |
+| TestWindows.rb:8:1:8:18 | # lgtm: blah blah\r |  lgtm: blah blah\r | lgtm | TestWindows.rb:8:1:8:18 | suppression range |
+| TestWindows.rb:9:1:9:32 | # lgtm blah blah #falsepositive\r |  lgtm blah blah #falsepositive\r | lgtm | TestWindows.rb:9:1:9:32 | suppression range |
+| TestWindows.rb:10:1:10:34 | #lgtm  [rb/confusing-method-name]\r | lgtm  [rb/confusing-method-name]\r | lgtm  [rb/confusing-method-name] | TestWindows.rb:10:1:10:34 | suppression range |
+| TestWindows.rb:11:1:11:9 | # lgtm[]\r |  lgtm[]\r | lgtm[] | TestWindows.rb:11:1:11:9 | suppression range |
+| TestWindows.rb:13:1:13:6 | #lgtm\r | lgtm\r | lgtm | TestWindows.rb:13:1:13:6 | suppression range |
+| TestWindows.rb:14:1:14:7 | #\tlgtm\r | \tlgtm\r | lgtm | TestWindows.rb:14:1:14:7 | suppression range |
+| TestWindows.rb:15:1:15:34 | # lgtm\t[rb/confusing-method-name]\r |  lgtm\t[rb/confusing-method-name]\r | lgtm\t[rb/confusing-method-name] | TestWindows.rb:15:1:15:34 | suppression range |
+| TestWindows.rb:18:1:18:12 | # foo; lgtm\r |  foo; lgtm\r | lgtm | TestWindows.rb:18:1:18:12 | suppression range |
+| TestWindows.rb:19:1:19:38 | # foo; lgtm[rb/confusing-method-name]\r |  foo; lgtm[rb/confusing-method-name]\r | lgtm[rb/confusing-method-name] | TestWindows.rb:19:1:19:38 | suppression range |
+| TestWindows.rb:21:1:21:37 | # foo lgtm[rb/confusing-method-name]\r |  foo lgtm[rb/confusing-method-name]\r | lgtm[rb/confusing-method-name] | TestWindows.rb:21:1:21:37 | suppression range |
+| TestWindows.rb:23:1:23:41 | # foo lgtm[rb/confusing-method-name] bar\r |  foo lgtm[rb/confusing-method-name] bar\r | lgtm[rb/confusing-method-name] | TestWindows.rb:23:1:23:41 | suppression range |
+| TestWindows.rb:24:1:24:8 | # LGTM!\r |  LGTM!\r | LGTM | TestWindows.rb:24:1:24:8 | suppression range |
+| TestWindows.rb:25:1:25:33 | # LGTM[rb/confusing-method-name]\r |  LGTM[rb/confusing-method-name]\r | LGTM[rb/confusing-method-name] | TestWindows.rb:25:1:25:33 | suppression range |
+| TestWindows.rb:26:1:26:74 | #lgtm[rb/confusing-method-name] and lgtm[rb/non-short-circuit-evaluation]\r | lgtm[rb/confusing-method-name] and lgtm[rb/non-short-circuit-evaluation]\r | lgtm[rb/confusing-method-name] | TestWindows.rb:26:1:26:74 | suppression range |
+| TestWindows.rb:26:1:26:74 | #lgtm[rb/confusing-method-name] and lgtm[rb/non-short-circuit-evaluation]\r | lgtm[rb/confusing-method-name] and lgtm[rb/non-short-circuit-evaluation]\r | lgtm[rb/non-short-circuit-evaluation] | TestWindows.rb:26:1:26:74 | suppression range |
+| TestWindows.rb:27:1:27:38 | #lgtm[rb/confusing-method-name]; lgtm\r | lgtm[rb/confusing-method-name]; lgtm\r | lgtm | TestWindows.rb:27:1:27:38 | suppression range |
+| TestWindows.rb:27:1:27:38 | #lgtm[rb/confusing-method-name]; lgtm\r | lgtm[rb/confusing-method-name]; lgtm\r | lgtm[rb/confusing-method-name] | TestWindows.rb:27:1:27:38 | suppression range |
diff --git a/ql/test/query-tests/AlertSuppression/AlertSuppression.qlref b/ql/test/query-tests/AlertSuppression/AlertSuppression.qlref
new file mode 100644
index 00000000000..9d7833eccae
--- /dev/null
+++ b/ql/test/query-tests/AlertSuppression/AlertSuppression.qlref
@@ -0,0 +1 @@
+AlertSuppression.ql
diff --git a/ql/test/query-tests/AlertSuppression/Test.rb b/ql/test/query-tests/AlertSuppression/Test.rb
new file mode 100644
index 00000000000..028d5b87aa7
--- /dev/null
+++ b/ql/test/query-tests/AlertSuppression/Test.rb
@@ -0,0 +1,28 @@
+class Test end # lgtm
+# lgtm[rb/confusing-method-name]
+# lgtm[rb/confusing-method-name, rb/non-short-circuit-evaluation]
+# lgtm[@tag:exceptions]
+# lgtm[@tag:exceptions,rb/confusing-method-name]
+# lgtm[@expires:2017-06-11]
+# lgtm[rb/confusing-method-name] does not seem confusing despite alert by lgtm
+# lgtm: blah blah
+# lgtm blah blah #falsepositive
+#lgtm  [rb/confusing-method-name]
+# lgtm[]
+# lgtmfoo
+#lgtm
+#	lgtm
+# lgtm	[rb/confusing-method-name]
+# foolgtm[rb/confusing-method-name]
+# foolgtm
+# foo; lgtm
+# foo; lgtm[rb/confusing-method-name]
+# foo lgtm
+# foo lgtm[rb/confusing-method-name]
+# foo lgtm bar
+# foo lgtm[rb/confusing-method-name] bar
+# LGTM!
+# LGTM[rb/confusing-method-name]
+#lgtm[rb/confusing-method-name] and lgtm[rb/non-short-circuit-evaluation]
+#lgtm[rb/confusing-method-name]; lgtm
+
diff --git a/ql/test/query-tests/AlertSuppression/TestWindows.rb b/ql/test/query-tests/AlertSuppression/TestWindows.rb
new file mode 100644
index 00000000000..1e69a66ee11
--- /dev/null
+++ b/ql/test/query-tests/AlertSuppression/TestWindows.rb
@@ -0,0 +1,28 @@
+class TestWindows end # lgtm
+# lgtm[rb/confusing-method-name]
+# lgtm[rb/confusing-method-name, rb/non-short-circuit-evaluation]
+# lgtm[@tag:exceptions]
+# lgtm[@tag:exceptions,rb/confusing-method-name]
+# lgtm[@expires:2017-06-11]
+# lgtm[rb/confusing-method-name] does not seem confusing despite alert by lgtm
+# lgtm: blah blah
+# lgtm blah blah #falsepositive
+#lgtm  [rb/confusing-method-name]
+# lgtm[]
+# lgtmfoo
+#lgtm
+#	lgtm
+# lgtm	[rb/confusing-method-name]
+# foolgtm[rb/confusing-method-name]
+# foolgtm
+# foo; lgtm
+# foo; lgtm[rb/confusing-method-name]
+# foo lgtm
+# foo lgtm[rb/confusing-method-name]
+# foo lgtm bar
+# foo lgtm[rb/confusing-method-name] bar
+# LGTM!
+# LGTM[rb/confusing-method-name]
+#lgtm[rb/confusing-method-name] and lgtm[rb/non-short-circuit-evaluation]
+#lgtm[rb/confusing-method-name]; lgtm
+