diff --git a/command/build.go b/command/build.go
index c11d4b124..410f1889d 100644
--- a/command/build.go
+++ b/command/build.go
@@ -135,8 +135,11 @@ func (c *BuildCommand) RunContext(buildCtx context.Context, cla *BuildArgs) int
 	}
 
 	builds, diags := packerStarter.GetBuilds(packer.GetBuildsOptions{
-		Only:   cla.Only,
-		Except: cla.Except,
+		Only:    cla.Only,
+		Except:  cla.Except,
+		Debug:   cla.Debug,
+		Force:   cla.Force,
+		OnError: cla.OnError,
 	})
 
 	// here, something could have gone wrong but we still want to run valid
@@ -186,6 +189,8 @@ func (c *BuildCommand) RunContext(buildCtx context.Context, cla *BuildArgs) int
 	log.Printf("On error: %v", cla.OnError)
 
 	// Set the debug and force mode and prepare all the builds
+	// This is only affects json templates, because HCL2
+	// templates have already been prepared in GetBuilds() above.
 	for i := range builds {
 		b := builds[i]
 		log.Printf("Preparing build: %s", b.Name())
diff --git a/hcl2template/types.packer_config.go b/hcl2template/types.packer_config.go
index 96293eb18..4ca0eba9e 100644
--- a/hcl2template/types.packer_config.go
+++ b/hcl2template/types.packer_config.go
@@ -311,7 +311,7 @@ func (cfg *PackerConfig) GetBuilds(opts packer.GetBuildsOptions) ([]packer.Build
 				}
 			}
 
-			builder, moreDiags, generatedVars := cfg.startBuilder(src, cfg.EvalContext(nil))
+			builder, moreDiags, generatedVars := cfg.startBuilder(src, cfg.EvalContext(nil), opts)
 			diags = append(diags, moreDiags...)
 			if moreDiags.HasErrors() {
 				continue
diff --git a/hcl2template/types.source.go b/hcl2template/types.source.go
index c44fb2687..dbc5a9724 100644
--- a/hcl2template/types.source.go
+++ b/hcl2template/types.source.go
@@ -2,6 +2,7 @@ package hcl2template
 
 import (
 	"fmt"
+	"strconv"
 
 	"github.com/hashicorp/hcl/v2"
 	"github.com/hashicorp/packer/packer"
@@ -38,7 +39,7 @@ func (p *Parser) decodeSource(block *hcl.Block) (*SourceBlock, hcl.Diagnostics)
 	return source, diags
 }
 
-func (cfg *PackerConfig) startBuilder(source *SourceBlock, ectx *hcl.EvalContext) (packer.Builder, hcl.Diagnostics, []string) {
+func (cfg *PackerConfig) startBuilder(source *SourceBlock, ectx *hcl.EvalContext, opts packer.GetBuildsOptions) (packer.Builder, hcl.Diagnostics, []string) {
 	var diags hcl.Diagnostics
 
 	builder, err := cfg.builderSchemas.Start(source.Type)
@@ -57,12 +58,23 @@ func (cfg *PackerConfig) startBuilder(source *SourceBlock, ectx *hcl.EvalContext
 		return nil, diags, nil
 	}
 
-	generatedVars, warning, err := builder.Prepare(source.builderVariables(), decoded)
+	// Note: HCL prepares inside of the Start func, but Json does not. Json
+	// builds are instead prepared only in command/build.go
+	// TODO: either make json prepare when plugins are loaded, or make HCL
+	// prepare at a later step, to make builds from different template types
+	// easier to reason about.
+	builderVars := source.builderVariables()
+	builderVars["packer_debug"] = strconv.FormatBool(opts.Debug)
+	builderVars["packer_force"] = strconv.FormatBool(opts.Force)
+	builderVars["packer_on_error"] = opts.OnError
+
+	generatedVars, warning, err := builder.Prepare(builderVars, decoded)
 	moreDiags = warningErrorsToDiags(source.block, warning, err)
 	diags = append(diags, moreDiags...)
 	return builder, diags, generatedVars
 }
 
+// These variables will populate the PackerConfig inside of the builders.
 func (source *SourceBlock) builderVariables() map[string]string {
 	return map[string]string{
 		"packer_build_name":   source.Name,
diff --git a/main.go b/main.go
index 9d13a7f9a..8d4c5ee38 100644
--- a/main.go
+++ b/main.go
@@ -146,6 +146,11 @@ func wrappedMain() int {
 		runtime.Version(),
 		runtime.GOOS, runtime.GOARCH)
 
+	// The config being loaded here is the Packer config -- it defines
+	// the location of third party builder plugins, plugin ports to use, and
+	// whether to disable telemetry. It is a global config.
+	// Do not confuse this config with the .json Packer template which gets
+	// passed into commands like `packer build`
 	config, err := loadConfig()
 	if err != nil {
 		fmt.Fprintf(os.Stderr, "Error loading configuration: \n\n%s\n", err)
@@ -328,6 +333,7 @@ func loadConfig() (*config, error) {
 	}
 	defer f.Close()
 
+	// This loads a json config, defined in packer/config.go
 	if err := decodeConfig(f, &config); err != nil {
 		return nil, err
 	}
diff --git a/packer/core.go b/packer/core.go
index 5faf56ae7..fcf72a6c5 100644
--- a/packer/core.go
+++ b/packer/core.go
@@ -199,6 +199,8 @@ func (c *Core) generateCoreBuildProvisioner(rawP *template.Provisioner, rawName
 	return cbp, nil
 }
 
+// This is used for json templates to launch the build plugins.
+// They will be prepared via b.Prepare() later.
 func (c *Core) GetBuilds(opts GetBuildsOptions) ([]Build, hcl.Diagnostics) {
 	buildNames := c.BuildNames(opts.Only, opts.Except)
 	builds := []Build{}
@@ -225,6 +227,12 @@ func (c *Core) Build(n string) (Build, error) {
 	if !ok {
 		return nil, fmt.Errorf("no such build found: %s", n)
 	}
+	// BuilderStore = config.Builders, gathered in loadConfig() in main.go
+	// For reference, the builtin BuilderStore is generated in
+	// packer/config.go in the Discover() func.
+
+	// the Start command launches the builder plugin of the given type without
+	// calling Prepare() or passing any build-specific details.
 	builder, err := c.components.BuilderStore.Start(configBuilder.Type)
 	if err != nil {
 		return nil, fmt.Errorf(
@@ -315,6 +323,8 @@ func (c *Core) Build(n string) (Build, error) {
 
 	// TODO hooks one day
 
+	// Return a structure that contains the plugins, their types, variables, and
+	// the raw builder config loaded from the json template
 	return &CoreBuild{
 		Type:               n,
 		Builder:            builder,
diff --git a/packer/run_interfaces.go b/packer/run_interfaces.go
index 8403a0b53..02048f6df 100644
--- a/packer/run_interfaces.go
+++ b/packer/run_interfaces.go
@@ -6,6 +6,8 @@ type GetBuildsOptions struct {
 	// Get builds except the ones that match with except and with only the ones
 	// that match with Only. When those are empty everything matches.
 	Except, Only []string
+	Debug, Force bool
+	OnError      string
 }
 
 type BuildGetter interface {