diff --git a/spec/api/plugin-api.spec.js b/spec/api/plugin-api.spec.js
new file mode 100644
index 0000000..72ea702
--- /dev/null
+++ b/spec/api/plugin-api.spec.js
@@ -0,0 +1,156 @@
+describe("plugin API", function() {
+  beforeEach(function() {
+    this.addMatchers({
+      toBeObject: function() {
+        this.message = function() {
+          return "Expected " + jasmine.pp(this.actual) + " "
+               + (this.isNot ? "not " : "")
+               + "to be an object.";
+        };
+
+        return this.actual !== null && typeof this.actual === "object";
+      },
+
+      toBeArray: function() {
+        this.message = function() {
+          return "Expected " + jasmine.pp(this.actual) + " "
+               + (this.isNot ? "not " : "")
+               + "to be an array.";
+        };
+
+        return Object.prototype.toString.apply(this.actual) === "[object Array]";
+      },
+
+      toBeFunction: function() {
+        this.message = function() {
+          return "Expected " + jasmine.pp(this.actual) + " "
+               + (this.isNot ? "not " : "")
+               + "to be a function.";
+        };
+
+        return typeof this.actual === "function";
+      },
+    });
+  });
+
+  describe("use", function() {
+    var grammar = 'start = "a"';
+
+    it("is called for each plugin", function() {
+      var pluginsUsed = [false, false, false],
+          plugins     = [
+            { use: function() { pluginsUsed[0] = true; } },
+            { use: function() { pluginsUsed[1] = true; } },
+            { use: function() { pluginsUsed[2] = true; } }
+          ];
+
+      PEG.buildParser(grammar, { plugins: plugins });
+
+      expect(pluginsUsed).toEqual([true, true, true]);
+    });
+
+    it("receives the configuration", function() {
+      var plugin = {
+            use: function(config, options) {
+              var i;
+
+              expect(config).toBeObject();
+
+              expect(config.parser).toBeObject();
+              expect(config.parser.parse('start = "a"')).toBeObject();
+
+              expect(config.passes).toBeObject();
+
+              expect(config.passes.check).toBeArray();
+              for (i = 0; i < config.passes.check.length; i++) {
+                expect(config.passes.check[i]).toBeFunction();
+              }
+
+              expect(config.passes.transform).toBeArray();
+              for (i = 0; i < config.passes.transform.length; i++) {
+                expect(config.passes.transform[i]).toBeFunction();
+              }
+
+              expect(config.passes.generate).toBeArray();
+              for (i = 0; i < config.passes.generate.length; i++) {
+                expect(config.passes.generate[i]).toBeFunction();
+              }
+            }
+          };
+
+      PEG.buildParser(grammar, { plugins: [plugin] });
+    });
+
+    it("receives the options", function() {
+      var buildParserOptions = { foo: 42 },
+          plugin             = {
+            use: function(config, options) {
+              expect(options).toEqual(buildParserOptions);
+            }
+          };
+
+      PEG.buildParser(grammar, buildParserOptions);
+    });
+
+    it("can replace the parser", function() {
+      var plugin = {
+            use: function(config, options) {
+              var parser = PEG.buildParser([
+                    'start = .* {',
+                    '  return {',
+                    '    type:  "grammar",',
+                    '    rules: [',
+                    '      {',
+                    '        type:       "rule",',
+                    '        expression: { type: "literal",  value: text(), ignoreCase: false }',
+                    '      }',
+                    '    ]',
+                    '  };',
+                    '}'
+                  ].join("\n"));
+
+              config.parser = parser;
+            }
+          },
+          parser = PEG.buildParser('a', { plugins: [plugin] });
+
+      expect(parser.parse("a")).toBe("a");
+    });
+
+    it("can change compiler passes", function() {
+      var plugin = {
+            use: function(config, options) {
+              var pass = function(ast) {
+                    ast.code = '({ parse: function() { return 42; } })';
+                  };
+
+              config.passes.generate = [pass];
+            }
+          },
+          parser = PEG.buildParser(grammar, { plugins: [plugin] });
+
+      expect(parser.parse("a")).toBe(42);
+    });
+
+    it("can change the options", function() {
+      var grammar = [
+            'a = "x"',
+            'b = "x"',
+            'c = "x"'
+          ].join("\n"),
+          plugin  = {
+            use: function(config, options) {
+              options.allowedStartRules = ["b", "c"];
+            }
+          },
+          parser  = PEG.buildParser(grammar, {
+            allowedStartRules: ["a"],
+            plugins:           [plugin]
+          });
+
+      expect(function() { parser.parse("x", { startRule: "a" }); }).toThrow();
+      expect(parser.parse("x", { startRule: "b" })).toBe("x");
+      expect(parser.parse("x", { startRule: "c" })).toBe("x");
+    });
+  });
+});
diff --git a/spec/index.html b/spec/index.html
index c931c11..bd0d668 100644
--- a/spec/index.html
+++ b/spec/index.html
@@ -14,6 +14,7 @@
     <script src="unit/compiler/passes/remove-proxy-rules.spec.js"></script>
     <script src="unit/compiler/passes/generate-bytecode.spec.js"></script>
     <script src="api/pegjs-api.spec.js"></script>
+    <script src="api/plugin-api.spec.js"></script>
     <script src="api/generated-parser.spec.js"></script>
     <script>
       (function() {