diff --git a/server/events/apply_executor.go b/server/events/apply_executor.go
index 6562d8ab8..dbacf35a6 100644
--- a/server/events/apply_executor.go
+++ b/server/events/apply_executor.go
@@ -16,10 +16,10 @@ package events
 import (
 	"github.com/runatlantis/atlantis/server/events/models"
 	"github.com/runatlantis/atlantis/server/events/run"
+	"github.com/runatlantis/atlantis/server/events/runtime"
 	"github.com/runatlantis/atlantis/server/events/terraform"
 	"github.com/runatlantis/atlantis/server/events/vcs"
 	"github.com/runatlantis/atlantis/server/events/webhooks"
-	"github.com/runatlantis/atlantis/server/events/yaml"
 )
 
 // ApplyExecutor handles executing terraform apply.
@@ -31,7 +31,7 @@ type ApplyExecutor struct {
 	AtlantisWorkspace AtlantisWorkspace
 	ProjectLocker     *DefaultProjectLocker
 	Webhooks          webhooks.Sender
-	ExecutionPlanner  *yaml.ExecutionPlanner
+	ExecutionPlanner  *runtime.ExecutionPlanner
 }
 
 // Execute executes apply for the ctx.
diff --git a/server/events/plan_executor.go b/server/events/plan_executor.go
index a620f2cb4..7e9291755 100644
--- a/server/events/plan_executor.go
+++ b/server/events/plan_executor.go
@@ -19,9 +19,9 @@ import (
 	"github.com/runatlantis/atlantis/server/events/locking"
 	"github.com/runatlantis/atlantis/server/events/models"
 	"github.com/runatlantis/atlantis/server/events/run"
+	"github.com/runatlantis/atlantis/server/events/runtime"
 	"github.com/runatlantis/atlantis/server/events/terraform"
 	"github.com/runatlantis/atlantis/server/events/vcs"
-	"github.com/runatlantis/atlantis/server/events/yaml"
 )
 
 //go:generate pegomock generate -m --use-experimental-model-gen --package mocks -o mocks/mock_lock_url_generator.go LockURLGenerator
@@ -39,7 +39,7 @@ type PlanExecutor struct {
 	Workspace        AtlantisWorkspace
 	ProjectFinder    ProjectFinder
 	ProjectLocker    ProjectLocker
-	ExecutionPlanner *yaml.ExecutionPlanner
+	ExecutionPlanner *runtime.ExecutionPlanner
 	LockURLGenerator LockURLGenerator
 }
 
diff --git a/server/events/project_locker_test.go b/server/events/project_locker_test.go
index fd9550348..cd6c80d91 100644
--- a/server/events/project_locker_test.go
+++ b/server/events/project_locker_test.go
@@ -55,8 +55,8 @@ package events_test
 //	When(l.TryLock(project, "", ctx.Pull, ctx.User)).ThenReturn(locking.TryLockResponse{
 //		LockAcquired: true,
 //	}, nil)
-//	When(p.ConfigReader.Exists("")).ThenReturn(true)
-//	When(p.ConfigReader.Read("")).ThenReturn(events.ProjectConfig{}, errors.New("err"))
+//	When(p.ParserValidator.Exists("")).ThenReturn(true)
+//	When(p.ParserValidator.Read("")).ThenReturn(events.ProjectConfig{}, errors.New("err"))
 //
 //	res := p.Execute(&ctx, "", project)
 //	Equals(t, "err", res.ProjectResult.Error.Error())
@@ -68,8 +68,8 @@ package events_test
 //	When(l.TryLock(project, "", ctx.Pull, ctx.User)).ThenReturn(locking.TryLockResponse{
 //		LockAcquired: true,
 //	}, nil)
-//	When(p.ConfigReader.Exists("")).ThenReturn(true)
-//	When(p.ConfigReader.Read("")).ThenReturn(events.ProjectConfig{
+//	When(p.ParserValidator.Exists("")).ThenReturn(true)
+//	When(p.ParserValidator.Read("")).ThenReturn(events.ProjectConfig{
 //		PreInit: []string{"pre-init"},
 //	}, nil)
 //	tfVersion, _ := version.NewVersion("0.9.0")
@@ -86,8 +86,8 @@ package events_test
 //	When(l.TryLock(project, "", ctx.Pull, ctx.User)).ThenReturn(locking.TryLockResponse{
 //		LockAcquired: true,
 //	}, nil)
-//	When(p.ConfigReader.Exists("")).ThenReturn(true)
-//	When(p.ConfigReader.Read("")).ThenReturn(events.ProjectConfig{}, nil)
+//	When(p.ParserValidator.Exists("")).ThenReturn(true)
+//	When(p.ParserValidator.Read("")).ThenReturn(events.ProjectConfig{}, nil)
 //	tfVersion, _ := version.NewVersion("0.9.0")
 //	When(tm.Version()).ThenReturn(tfVersion)
 //	When(tm.Init(ctx.Log, "", "", nil, tfVersion)).ThenReturn(nil, errors.New("err"))
@@ -102,8 +102,8 @@ package events_test
 //	When(l.TryLock(project, "", ctx.Pull, ctx.User)).ThenReturn(locking.TryLockResponse{
 //		LockAcquired: true,
 //	}, nil)
-//	When(p.ConfigReader.Exists("")).ThenReturn(true)
-//	When(p.ConfigReader.Read("")).ThenReturn(events.ProjectConfig{
+//	When(p.ParserValidator.Exists("")).ThenReturn(true)
+//	When(p.ParserValidator.Read("")).ThenReturn(events.ProjectConfig{
 //		PreGet: []string{"pre-get"},
 //	}, nil)
 //	tfVersion, _ := version.NewVersion("0.8")
@@ -120,8 +120,8 @@ package events_test
 //	When(l.TryLock(project, "", ctx.Pull, ctx.User)).ThenReturn(locking.TryLockResponse{
 //		LockAcquired: true,
 //	}, nil)
-//	When(p.ConfigReader.Exists("")).ThenReturn(true)
-//	When(p.ConfigReader.Read("")).ThenReturn(events.ProjectConfig{}, nil)
+//	When(p.ParserValidator.Exists("")).ThenReturn(true)
+//	When(p.ParserValidator.Read("")).ThenReturn(events.ProjectConfig{}, nil)
 //	tfVersion, _ := version.NewVersion("0.8")
 //	When(tm.Version()).ThenReturn(tfVersion)
 //	When(tm.RunCommandWithVersion(ctx.Log, "", []string{"get", "-no-color"}, tfVersion, "")).ThenReturn("", errors.New("err"))
@@ -136,8 +136,8 @@ package events_test
 //	When(l.TryLock(project, "", ctx.Pull, ctx.User)).ThenReturn(locking.TryLockResponse{
 //		LockAcquired: true,
 //	}, nil)
-//	When(p.ConfigReader.Exists("")).ThenReturn(true)
-//	When(p.ConfigReader.Read("")).ThenReturn(events.ProjectConfig{
+//	When(p.ParserValidator.Exists("")).ThenReturn(true)
+//	When(p.ParserValidator.Read("")).ThenReturn(events.ProjectConfig{
 //		PrePlan: []string{"command"},
 //	}, nil)
 //	tfVersion, _ := version.NewVersion("0.9")
@@ -156,11 +156,11 @@ package events_test
 //		LockAcquired: true,
 //	}
 //	When(l.TryLock(project, "", ctx.Pull, ctx.User)).ThenReturn(lockResponse, nil)
-//	When(p.ConfigReader.Exists("")).ThenReturn(true)
+//	When(p.ParserValidator.Exists("")).ThenReturn(true)
 //	config := events.ProjectConfig{
 //		PreInit: []string{"pre-init"},
 //	}
-//	When(p.ConfigReader.Read("")).ThenReturn(config, nil)
+//	When(p.ParserValidator.Read("")).ThenReturn(config, nil)
 //	tfVersion, _ := version.NewVersion("0.9")
 //	When(tm.Version()).ThenReturn(tfVersion)
 //	When(tm.Init(ctx.Log, "", "", nil, tfVersion)).ThenReturn(nil, nil)
@@ -182,11 +182,11 @@ package events_test
 //		LockAcquired: true,
 //	}
 //	When(l.TryLock(project, "", ctx.Pull, ctx.User)).ThenReturn(lockResponse, nil)
-//	When(p.ConfigReader.Exists("")).ThenReturn(true)
+//	When(p.ParserValidator.Exists("")).ThenReturn(true)
 //	config := events.ProjectConfig{
 //		PreGet: []string{"pre-get"},
 //	}
-//	When(p.ConfigReader.Read("")).ThenReturn(config, nil)
+//	When(p.ParserValidator.Read("")).ThenReturn(config, nil)
 //	tfVersion, _ := version.NewVersion("0.8")
 //	When(tm.Version()).ThenReturn(tfVersion)
 //
@@ -207,11 +207,11 @@ package events_test
 //		LockAcquired: true,
 //	}
 //	When(l.TryLock(project, "", ctx.Pull, ctx.User)).ThenReturn(lockResponse, nil)
-//	When(p.ConfigReader.Exists("")).ThenReturn(true)
+//	When(p.ParserValidator.Exists("")).ThenReturn(true)
 //	config := events.ProjectConfig{
 //		PrePlan: []string{"command"},
 //	}
-//	When(p.ConfigReader.Read("")).ThenReturn(config, nil)
+//	When(p.ParserValidator.Read("")).ThenReturn(config, nil)
 //	tfVersion, _ := version.NewVersion("0.9")
 //	When(tm.Version()).ThenReturn(tfVersion)
 //
@@ -231,11 +231,11 @@ package events_test
 //		LockAcquired: true,
 //	}
 //	When(l.TryLock(project, "", ctx.Pull, ctx.User)).ThenReturn(lockResponse, nil)
-//	When(p.ConfigReader.Exists("")).ThenReturn(true)
+//	When(p.ParserValidator.Exists("")).ThenReturn(true)
 //	config := events.ProjectConfig{
 //		PreApply: []string{"command"},
 //	}
-//	When(p.ConfigReader.Read("")).ThenReturn(config, nil)
+//	When(p.ParserValidator.Read("")).ThenReturn(config, nil)
 //	tfVersion, _ := version.NewVersion("0.9")
 //	When(tm.Version()).ThenReturn(tfVersion)
 //
@@ -262,7 +262,7 @@ package events_test
 //	r := rmocks.NewMockRunner()
 //	return &events.DefaultProjectLocker{
 //		Locker:       l,
-//		ConfigReader: cr,
+//		ParserValidator: cr,
 //		Terraform:    tm,
 //		Run:          r,
 //	}, l, tm, r
diff --git a/server/events/yaml/apply_step.go b/server/events/runtime/apply_step.go
similarity index 97%
rename from server/events/yaml/apply_step.go
rename to server/events/runtime/apply_step.go
index 4b6a36061..359141481 100644
--- a/server/events/yaml/apply_step.go
+++ b/server/events/runtime/apply_step.go
@@ -1,4 +1,4 @@
-package yaml
+package runtime
 
 import (
 	"fmt"
diff --git a/server/events/yaml/apply_step_test.go b/server/events/runtime/apply_step_test.go
similarity index 90%
rename from server/events/yaml/apply_step_test.go
rename to server/events/runtime/apply_step_test.go
index f2066140e..862f5e10e 100644
--- a/server/events/yaml/apply_step_test.go
+++ b/server/events/runtime/apply_step_test.go
@@ -1,4 +1,4 @@
-package yaml_test
+package runtime_test
 
 import (
 	"io/ioutil"
@@ -9,14 +9,14 @@ import (
 	. "github.com/petergtz/pegomock"
 	"github.com/runatlantis/atlantis/server/events/mocks/matchers"
 	matchers2 "github.com/runatlantis/atlantis/server/events/run/mocks/matchers"
+	"github.com/runatlantis/atlantis/server/events/runtime"
 	"github.com/runatlantis/atlantis/server/events/terraform/mocks"
-	"github.com/runatlantis/atlantis/server/events/yaml"
 	. "github.com/runatlantis/atlantis/testing"
 )
 
 func TestRun_NoDir(t *testing.T) {
-	s := yaml.ApplyStep{
-		Meta: yaml.StepMeta{
+	s := runtime.ApplyStep{
+		Meta: runtime.StepMeta{
 			Workspace:             "workspace",
 			AbsolutePath:          "nonexistent/path",
 			DirRelativeToRepoRoot: ".",
@@ -33,8 +33,8 @@ func TestRun_NoPlanFile(t *testing.T) {
 	tmpDir, cleanup := TempDir(t)
 	defer cleanup()
 
-	s := yaml.ApplyStep{
-		Meta: yaml.StepMeta{
+	s := runtime.ApplyStep{
+		Meta: runtime.StepMeta{
 			Workspace:             "workspace",
 			AbsolutePath:          tmpDir,
 			DirRelativeToRepoRoot: ".",
@@ -58,8 +58,8 @@ func TestRun_Success(t *testing.T) {
 	terraform := mocks.NewMockClient()
 
 	tfVersion, _ := version.NewVersion("0.11.4")
-	s := yaml.ApplyStep{
-		Meta: yaml.StepMeta{
+	s := runtime.ApplyStep{
+		Meta: runtime.StepMeta{
 			Workspace:             "workspace",
 			AbsolutePath:          tmpDir,
 			DirRelativeToRepoRoot: ".",
diff --git a/server/events/yaml/execution_planner.go b/server/events/runtime/execution_planner.go
similarity index 93%
rename from server/events/yaml/execution_planner.go
rename to server/events/runtime/execution_planner.go
index c34903400..012d6b008 100644
--- a/server/events/yaml/execution_planner.go
+++ b/server/events/runtime/execution_planner.go
@@ -1,17 +1,23 @@
-package yaml
+package runtime
 
 import (
 	"fmt"
+	"os"
 	"path/filepath"
 
 	"github.com/hashicorp/go-version"
+	"github.com/runatlantis/atlantis/server/events/yaml"
 	"github.com/runatlantis/atlantis/server/logging"
 )
 
+const PlanStageName = "plan"
+const ApplyStageName = "apply"
+const AtlantisYAMLFilename = "atlantis.yaml"
+
 type ExecutionPlanner struct {
 	TerraformExecutor TerraformExec
 	DefaultTFVersion  *version.Version
-	ConfigReader      *Reader
+	ParserValidator   *yaml.ParserValidator
 }
 
 type TerraformExec interface {
@@ -30,17 +36,18 @@ func (s *ExecutionPlanner) BuildPlanStage(log *logging.SimpleLogger, repoDir str
 }
 
 func (s *ExecutionPlanner) buildStage(stageName string, log *logging.SimpleLogger, repoDir string, workspace string, relProjectPath string, extraCommentArgs []string, username string, defaults []Step) ([]Step, error) {
-	config, err := s.ConfigReader.ReadConfig(repoDir)
-	if err != nil {
-		return nil, err
-	}
+	config, err := s.ParserValidator.ReadConfig(repoDir)
 
 	// If there's no config file, use defaults.
-	if config == nil {
+	if os.IsNotExist(err) {
 		log.Info("no %s file found––continuing with defaults", AtlantisYAMLFilename)
 		return defaults, nil
 	}
 
+	if err != nil {
+		return nil, err
+	}
+
 	// Get this project's configuration.
 	for _, p := range config.Projects {
 		if p.Dir == relProjectPath && p.Workspace == workspace {
@@ -61,7 +68,7 @@ func (s *ExecutionPlanner) buildStage(stageName string, log *logging.SimpleLogge
 			// We have a workflow defined, so now we need to build it.
 			meta := s.buildMeta(log, repoDir, workspace, relProjectPath, extraCommentArgs, username)
 			var steps []Step
-			var stepsConfig []StepConfig
+			var stepsConfig []yaml.StepConfig
 			if stageName == PlanStageName {
 				stepsConfig = workflow.Plan.Steps
 			} else {
diff --git a/server/events/yaml/init_step.go b/server/events/runtime/init_step.go
similarity index 98%
rename from server/events/yaml/init_step.go
rename to server/events/runtime/init_step.go
index 235b90244..1bf5b8734 100644
--- a/server/events/yaml/init_step.go
+++ b/server/events/runtime/init_step.go
@@ -1,4 +1,4 @@
-package yaml
+package runtime
 
 // InitStep runs `terraform init`.
 type InitStep struct {
diff --git a/server/events/yaml/init_step_test.go b/server/events/runtime/init_step_test.go
similarity index 92%
rename from server/events/yaml/init_step_test.go
rename to server/events/runtime/init_step_test.go
index bfdbd84b5..911bcb233 100644
--- a/server/events/yaml/init_step_test.go
+++ b/server/events/runtime/init_step_test.go
@@ -1,4 +1,4 @@
-package yaml_test
+package runtime_test
 
 import (
 	"testing"
@@ -7,8 +7,8 @@ import (
 	. "github.com/petergtz/pegomock"
 	"github.com/runatlantis/atlantis/server/events/mocks/matchers"
 	matchers2 "github.com/runatlantis/atlantis/server/events/run/mocks/matchers"
+	"github.com/runatlantis/atlantis/server/events/runtime"
 	"github.com/runatlantis/atlantis/server/events/terraform/mocks"
-	"github.com/runatlantis/atlantis/server/events/yaml"
 	"github.com/runatlantis/atlantis/server/logging"
 	. "github.com/runatlantis/atlantis/testing"
 )
@@ -43,8 +43,8 @@ func TestRun_UsesGetOrInitForRightVersion(t *testing.T) {
 
 			tfVersion, _ := version.NewVersion(c.version)
 			logger := logging.NewNoopLogger()
-			s := yaml.InitStep{
-				Meta: yaml.StepMeta{
+			s := runtime.InitStep{
+				Meta: runtime.StepMeta{
 					Log:                   logger,
 					Workspace:             "workspace",
 					AbsolutePath:          "/path",
diff --git a/server/events/yaml/plan_step.go b/server/events/runtime/plan_step.go
similarity index 99%
rename from server/events/yaml/plan_step.go
rename to server/events/runtime/plan_step.go
index 99890e62e..b8d6b3ace 100644
--- a/server/events/yaml/plan_step.go
+++ b/server/events/runtime/plan_step.go
@@ -1,4 +1,4 @@
-package yaml
+package runtime
 
 import (
 	"fmt"
diff --git a/server/events/yaml/plan_step_test.go b/server/events/runtime/plan_step_test.go
similarity index 96%
rename from server/events/yaml/plan_step_test.go
rename to server/events/runtime/plan_step_test.go
index 91e9372d3..53b45c2e6 100644
--- a/server/events/yaml/plan_step_test.go
+++ b/server/events/runtime/plan_step_test.go
@@ -1,4 +1,4 @@
-package yaml_test
+package runtime_test
 
 import (
 	"errors"
@@ -11,8 +11,8 @@ import (
 	. "github.com/petergtz/pegomock"
 	"github.com/runatlantis/atlantis/server/events/mocks/matchers"
 	matchers2 "github.com/runatlantis/atlantis/server/events/run/mocks/matchers"
+	"github.com/runatlantis/atlantis/server/events/runtime"
 	"github.com/runatlantis/atlantis/server/events/terraform/mocks"
-	"github.com/runatlantis/atlantis/server/events/yaml"
 	"github.com/runatlantis/atlantis/server/logging"
 	. "github.com/runatlantis/atlantis/testing"
 )
@@ -25,8 +25,8 @@ func TestRun_NoWorkspaceIn08(t *testing.T) {
 	tfVersion, _ := version.NewVersion("0.8")
 	logger := logging.NewNoopLogger()
 	workspace := "default"
-	s := yaml.PlanStep{
-		Meta: yaml.StepMeta{
+	s := runtime.PlanStep{
+		Meta: runtime.StepMeta{
 			Log:                   logger,
 			Workspace:             workspace,
 			AbsolutePath:          "/path",
@@ -61,8 +61,8 @@ func TestRun_ErrWorkspaceIn08(t *testing.T) {
 	tfVersion, _ := version.NewVersion("0.8")
 	logger := logging.NewNoopLogger()
 	workspace := "notdefault"
-	s := yaml.PlanStep{
-		Meta: yaml.StepMeta{
+	s := runtime.PlanStep{
+		Meta: runtime.StepMeta{
 			Log:                   logger,
 			Workspace:             workspace,
 			AbsolutePath:          "/path",
@@ -112,8 +112,8 @@ func TestRun_SwitchesWorkspace(t *testing.T) {
 
 			tfVersion, _ := version.NewVersion(c.tfVersion)
 			logger := logging.NewNoopLogger()
-			s := yaml.PlanStep{
-				Meta: yaml.StepMeta{
+			s := runtime.PlanStep{
+				Meta: runtime.StepMeta{
 					Log:                   logger,
 					Workspace:             "workspace",
 					AbsolutePath:          "/path",
@@ -170,8 +170,8 @@ func TestRun_CreatesWorkspace(t *testing.T) {
 			terraform := mocks.NewMockClient()
 			tfVersion, _ := version.NewVersion(c.tfVersion)
 			logger := logging.NewNoopLogger()
-			s := yaml.PlanStep{
-				Meta: yaml.StepMeta{
+			s := runtime.PlanStep{
+				Meta: runtime.StepMeta{
 					Log:                   logger,
 					Workspace:             "workspace",
 					AbsolutePath:          "/path",
@@ -212,8 +212,8 @@ func TestRun_NoWorkspaceSwitchIfNotNecessary(t *testing.T) {
 	terraform := mocks.NewMockClient()
 	tfVersion, _ := version.NewVersion("0.10.0")
 	logger := logging.NewNoopLogger()
-	s := yaml.PlanStep{
-		Meta: yaml.StepMeta{
+	s := runtime.PlanStep{
+		Meta: runtime.StepMeta{
 			Log:                   logger,
 			Workspace:             "workspace",
 			AbsolutePath:          "/path",
@@ -258,8 +258,8 @@ func TestRun_AddsEnvVarFile(t *testing.T) {
 	// Using version >= 0.10 here so we don't expect any env commands.
 	tfVersion, _ := version.NewVersion("0.10.0")
 	logger := logging.NewNoopLogger()
-	s := yaml.PlanStep{
-		Meta: yaml.StepMeta{
+	s := runtime.PlanStep{
+		Meta: runtime.StepMeta{
 			Log:                   logger,
 			Workspace:             "workspace",
 			AbsolutePath:          tmpDir,
diff --git a/server/events/yaml/repoconfig.go b/server/events/runtime/repoconfig.go
similarity index 99%
rename from server/events/yaml/repoconfig.go
rename to server/events/runtime/repoconfig.go
index 7af982436..138f73f0d 100644
--- a/server/events/yaml/repoconfig.go
+++ b/server/events/runtime/repoconfig.go
@@ -1,4 +1,4 @@
-package yaml
+package runtime
 
 import (
 	"github.com/hashicorp/go-version"
diff --git a/server/events/yaml/run_step.go b/server/events/runtime/run_step.go
similarity index 97%
rename from server/events/yaml/run_step.go
rename to server/events/runtime/run_step.go
index e4794a22c..ba6dbe385 100644
--- a/server/events/yaml/run_step.go
+++ b/server/events/runtime/run_step.go
@@ -1,4 +1,4 @@
-package yaml
+package runtime
 
 import (
 	"fmt"
diff --git a/server/events/runtime/run_step_test.go b/server/events/runtime/run_step_test.go
new file mode 100644
index 000000000..899327a69
--- /dev/null
+++ b/server/events/runtime/run_step_test.go
@@ -0,0 +1,3 @@
+package runtime_test
+
+// todo
diff --git a/server/events/runtime/runtime.go b/server/events/runtime/runtime.go
new file mode 100644
index 000000000..ea70550a6
--- /dev/null
+++ b/server/events/runtime/runtime.go
@@ -0,0 +1,4 @@
+// Package runtime handles constructing an execution graph for each action
+// based on configuration and defaults. The handlers can then execute this
+// graph.
+package runtime
diff --git a/server/events/yaml/reader.go b/server/events/yaml/parser_validator.go
similarity index 59%
rename from server/events/yaml/reader.go
rename to server/events/yaml/parser_validator.go
index eaea83539..861201504 100644
--- a/server/events/yaml/reader.go
+++ b/server/events/yaml/parser_validator.go
@@ -5,49 +5,46 @@ import (
 	"io/ioutil"
 	"os"
 	"path/filepath"
-	"strings"
 
 	"github.com/pkg/errors"
 	"gopkg.in/yaml.v2"
 )
 
+// AtlantisYAMLFilename is the name of the config file for each repo.
 const AtlantisYAMLFilename = "atlantis.yaml"
-const PlanStageName = "plan"
-const ApplyStageName = "apply"
 
-type Reader struct{}
+type ParserValidator struct{}
 
-// ReadConfig returns the parsed and validated config for repoDir.
-// If there was no config, it returns a nil pointer.
-func (r *Reader) ReadConfig(repoDir string) (*Config, error) {
+// ReadConfig returns the parsed and validated atlantis.yaml config for repoDir.
+// If there was no config file, then this can be detected by checking the type
+// of error: os.IsNotExist(error).
+func (r *ParserValidator) ReadConfig(repoDir string) (Config, error) {
 	configFile := filepath.Join(repoDir, AtlantisYAMLFilename)
 	configData, err := ioutil.ReadFile(configFile)
 
-	// If the file doesn't exist return nil.
+	// NOTE: the error we return here must also be os.IsNotExist since that's
+	// what our callers use to detect a missing config file.
 	if err != nil && os.IsNotExist(err) {
-		return nil, nil
+		return Config{}, err
 	}
 
 	// If it exists but we couldn't read it return an error.
 	if err != nil {
-		return nil, errors.Wrapf(err, "unable to read %s file", AtlantisYAMLFilename)
+		return Config{}, errors.Wrapf(err, "unable to read %s file", AtlantisYAMLFilename)
 	}
 
 	// If the config file exists, parse it.
 	config, err := r.parseAndValidate(configData)
 	if err != nil {
-		return nil, errors.Wrapf(err, "parsing %s", AtlantisYAMLFilename)
+		return Config{}, errors.Wrapf(err, "parsing %s", AtlantisYAMLFilename)
 	}
-	return &config, err
+	return config, err
 }
 
-func (r *Reader) parseAndValidate(configData []byte) (Config, error) {
+func (r *ParserValidator) parseAndValidate(configData []byte) (Config, error) {
 	var repoConfig Config
 	if err := yaml.UnmarshalStrict(configData, &repoConfig); err != nil {
-		// Unmarshal error messages aren't fit for user output. We need to
-		// massage them.
-		// todo: fix "field autoplan not found in struct yaml.alias" errors
-		return repoConfig, errors.New(strings.Replace(err.Error(), " into yaml.Config", "", -1))
+		return repoConfig, err
 	}
 
 	// Validate version.
diff --git a/server/events/yaml/reader_test.go b/server/events/yaml/parser_validator_test.go
similarity index 71%
rename from server/events/yaml/reader_test.go
rename to server/events/yaml/parser_validator_test.go
index 7dc4b25b4..4adc8ca34 100644
--- a/server/events/yaml/reader_test.go
+++ b/server/events/yaml/parser_validator_test.go
@@ -2,6 +2,7 @@ package yaml_test
 
 import (
 	"io/ioutil"
+	"os"
 	"path/filepath"
 	"testing"
 
@@ -10,20 +11,18 @@ import (
 )
 
 func TestReadConfig_DirDoesNotExist(t *testing.T) {
-	r := yaml.Reader{}
-	conf, err := r.ReadConfig("/not/exist")
-	Ok(t, err)
-	Assert(t, conf == nil, "exp nil ptr")
+	r := yaml.ParserValidator{}
+	_, err := r.ReadConfig("/not/exist")
+	Assert(t, os.IsNotExist(err), "exp nil ptr")
 }
 
 func TestReadConfig_FileDoesNotExist(t *testing.T) {
 	tmpDir, cleanup := TempDir(t)
 	defer cleanup()
 
-	r := yaml.Reader{}
-	conf, err := r.ReadConfig(tmpDir)
-	Ok(t, err)
-	Assert(t, conf == nil, "exp nil ptr")
+	r := yaml.ParserValidator{}
+	_, err := r.ReadConfig(tmpDir)
+	Assert(t, os.IsNotExist(err), "exp nil ptr")
 }
 
 func TestReadConfig_BadPermissions(t *testing.T) {
@@ -32,7 +31,7 @@ func TestReadConfig_BadPermissions(t *testing.T) {
 	err := ioutil.WriteFile(filepath.Join(tmpDir, "atlantis.yaml"), nil, 0000)
 	Ok(t, err)
 
-	r := yaml.Reader{}
+	r := yaml.ParserValidator{}
 	_, err = r.ReadConfig(tmpDir)
 	ErrContains(t, "unable to read atlantis.yaml file: ", err)
 }
@@ -48,7 +47,7 @@ func TestReadConfig_UnmarshalErrors(t *testing.T) {
 		{
 			"random characters",
 			"slkjds",
-			"parsing atlantis.yaml: yaml: unmarshal errors:\n  line 1: cannot unmarshal !!str `slkjds`",
+			"parsing atlantis.yaml: yaml: unmarshal errors:\n  line 1: cannot unmarshal !!str `slkjds` into yaml.Config",
 		},
 		{
 			"just a colon",
@@ -64,7 +63,7 @@ func TestReadConfig_UnmarshalErrors(t *testing.T) {
 		t.Run(c.description, func(t *testing.T) {
 			err := ioutil.WriteFile(filepath.Join(tmpDir, "atlantis.yaml"), []byte(c.input), 0600)
 			Ok(t, err)
-			r := yaml.Reader{}
+			r := yaml.ParserValidator{}
 			_, err = r.ReadConfig(tmpDir)
 			ErrEquals(t, c.expErr, err)
 		})
@@ -161,175 +160,6 @@ projects:
 - unknown: value`,
 			expErr: "yaml: unmarshal errors:\n  line 4: field unknown not found in struct yaml.alias",
 		},
-
-		// project workflow doesn't exist
-		// workflow has plan and apply keys (otherwise no point specifying it)
-		// plan/apply stages must have non-empty steps key
-
-		// Test the steps key.
-		{
-			description: "unsupported step type",
-			input: `
-version: 2
-projects:
-- dir: "."
-workflows:
-  default:
-    plan:
-      steps:
-      - unsupported`,
-			expErr: "unsupported step type: \"unsupported\"",
-		},
-
-		// Init step.
-		{
-			description: "unsupported arg to init step",
-			input: `
-version: 2
-projects:
-- dir: "."
-workflows:
-  default:
-    plan:
-      steps:
-      - init:
-          extra_args: ["hi"]
-          hi: bye
-`,
-			expErr: "unsupported key \"hi\" for step init – the only supported key is extra_args",
-		},
-		{
-			description: "invalid value type to init step's extra_args",
-			input: `
-version: 2
-projects:
-- dir: "."
-workflows:
-  default:
-    plan:
-      steps:
-      - init:
-          extra_args: arg
-`,
-			expErr: "expected array of strings as value of extra_args, not \"arg\"",
-		},
-
-		// Plan step.
-		{
-			description: "unsupported arg to plan step",
-			input: `
-version: 2
-projects:
-- dir: "."
-workflows:
-  default:
-    plan:
-      steps:
-      - plan:
-          extra_args: ["hi"]
-          hi: bye
-`,
-			expErr: "unsupported key \"hi\" for step plan – the only supported key is extra_args",
-		},
-		{
-			description: "invalid value type to plan step's extra_args",
-			input: `
-version: 2
-projects:
-- dir: "."
-workflows:
-  default:
-    plan:
-      steps:
-      - plan:
-          extra_args: arg
-`,
-			expErr: "expected array of strings as value of extra_args, not \"arg\"",
-		},
-
-		// Apply step.
-		{
-			description: "unsupported arg to apply step",
-			input: `
-version: 2
-projects:
-- dir: "."
-workflows:
-  default:
-    plan:
-      steps:
-      - apply:
-          extra_args: ["hi"]
-          hi: bye
-`,
-			expErr: "unsupported key \"hi\" for step apply – the only supported key is extra_args",
-		},
-		{
-			description: "invalid value type to apply step's extra_args",
-			input: `
-version: 2
-projects:
-- dir: "."
-workflows:
-  default:
-    plan:
-      steps:
-      - apply:
-          extra_args: arg
-`,
-			expErr: "expected array of strings as value of extra_args, not \"arg\"",
-		},
-		{
-			description: "invalid step type",
-			input: `
-version: 2
-projects:
-- dir: "."
-workflows:
-  default:
-    plan:
-      steps:
-      - rn: echo should fail
-`,
-			expErr: "yaml: unmarshal errors:\n  line 9: field rn not found in struct struct { Run string \"yaml:\\\"run\\\"\" }",
-		},
-		{
-			description: "missed the steps key and just set an array directly",
-			input: `
-version: 2
-projects:
-- dir: "."
-workflows:
-  default:
-    plan:
-      - init
-`,
-			expErr: "missing \"steps\" key",
-		},
-		{
-			description: "no value after plan:",
-			input: `
-version: 2
-projects:
-- dir: "."
-workflows:
-  default:
-    plan:
-`,
-			expErr: "missing \"steps\" key",
-		},
-		{
-			description: "no value after apply:",
-			input: `
-version: 2
-projects:
-- dir: "."
-workflows:
-  default:
-    plan:
-`,
-			expErr: "missing \"steps\" key",
-		},
 	}
 
 	tmpDir, cleanup := TempDir(t)
@@ -340,7 +170,7 @@ workflows:
 			err := ioutil.WriteFile(filepath.Join(tmpDir, "atlantis.yaml"), []byte(c.input), 0600)
 			Ok(t, err)
 
-			r := yaml.Reader{}
+			r := yaml.ParserValidator{}
 			_, err = r.ReadConfig(tmpDir)
 			ErrEquals(t, "parsing atlantis.yaml: "+c.expErr, err)
 		})
@@ -595,7 +425,7 @@ workflows:
 							Steps: []yaml.StepConfig{
 								{
 									StepType:  "init",
-									ExtraArgs: nil,
+									ExtraArgs: []string{},
 								},
 								{
 									StepType:  "plan",
@@ -642,18 +472,16 @@ workflows:
 						Plan: &yaml.Stage{
 							Steps: []yaml.StepConfig{
 								{
-									StepType:  "run",
-									ExtraArgs: nil,
-									Run:       []string{"echo", "plan hi"},
+									StepType: "run",
+									Run:      []string{"echo", "plan hi"},
 								},
 							},
 						},
 						Apply: &yaml.Stage{
 							Steps: []yaml.StepConfig{
 								{
-									StepType:  "run",
-									ExtraArgs: nil,
-									Run:       []string{"echo", "apply", "arg 2"},
+									StepType: "run",
+									Run:      []string{"echo", "apply", "arg 2"},
 								},
 							},
 						},
@@ -671,10 +499,10 @@ workflows:
 			err := ioutil.WriteFile(filepath.Join(tmpDir, "atlantis.yaml"), []byte(c.input), 0600)
 			Ok(t, err)
 
-			r := yaml.Reader{}
+			r := yaml.ParserValidator{}
 			act, err := r.ReadConfig(tmpDir)
 			Ok(t, err)
-			Equals(t, &c.expOutput, act)
+			Equals(t, c.expOutput, act)
 		})
 	}
 }
diff --git a/server/events/yaml/project.go b/server/events/yaml/project.go
index b2c136e59..dade99bae 100644
--- a/server/events/yaml/project.go
+++ b/server/events/yaml/project.go
@@ -9,12 +9,14 @@ type Project struct {
 	ApplyRequirements []string  `yaml:"apply_requirements"`
 }
 
+const DefaultWorkspace = "default"
+
 func (p *Project) UnmarshalYAML(unmarshal func(interface{}) error) error {
 	// Use a type alias so unmarshal doesn't get into an infinite loop.
 	type alias Project
 	// Set up defaults.
 	defaults := alias{
-		Workspace: defaultWorkspace,
+		Workspace: DefaultWorkspace,
 		AutoPlan: &AutoPlan{
 			Enabled:      true,
 			WhenModified: []string{"**/*.tf"},
diff --git a/server/events/yaml/run_step_test.go b/server/events/yaml/run_step_test.go
deleted file mode 100644
index d00e3ec78..000000000
--- a/server/events/yaml/run_step_test.go
+++ /dev/null
@@ -1,3 +0,0 @@
-package yaml
-
-// todo
diff --git a/server/events/yaml/yaml.go b/server/events/yaml/yaml.go
new file mode 100644
index 000000000..08b884cae
--- /dev/null
+++ b/server/events/yaml/yaml.go
@@ -0,0 +1,4 @@
+// Package yaml contains the golang representations of the YAML elements
+// supported in atlantis.yaml. Many of the elements implement UnmarshalYAML
+// in order to set defaults.
+package yaml
diff --git a/server/server.go b/server/server.go
index 9381d7469..8ae0e5b6e 100644
--- a/server/server.go
+++ b/server/server.go
@@ -37,6 +37,7 @@ import (
 	"github.com/runatlantis/atlantis/server/events/locking/boltdb"
 	"github.com/runatlantis/atlantis/server/events/models"
 	"github.com/runatlantis/atlantis/server/events/run"
+	"github.com/runatlantis/atlantis/server/events/runtime"
 	"github.com/runatlantis/atlantis/server/events/terraform"
 	"github.com/runatlantis/atlantis/server/events/vcs"
 	"github.com/runatlantis/atlantis/server/events/webhooks"
@@ -200,8 +201,8 @@ func NewServer(userConfig UserConfig, config Config) (*Server, error) {
 		ConfigReader: configReader,
 		Terraform:    terraformClient,
 	}
-	executionPlanner := &yaml.ExecutionPlanner{
-		ConfigReader:      &yaml.Reader{},
+	executionPlanner := &runtime.ExecutionPlanner{
+		ParserValidator:   &yaml.ParserValidator{},
 		DefaultTFVersion:  terraformClient.Version(),
 		TerraformExecutor: terraformClient,
 	}