diff --git a/internals/design/design.go b/internals/design/design.go
new file mode 100644
index 0000000..46baa77
--- /dev/null
+++ b/internals/design/design.go
@@ -0,0 +1,202 @@
+package simulation
+
+import "encoding/json"
+
+type Node struct {
+	ID       string                 `json:"id"`
+	Type     string                 `json:"type"`
+	Position Position               `josn:"position"`
+	Props    map[string]interface{} `json:"props"`
+}
+
+type Position struct {
+	X int `json:"x"`
+	Y int `json:"y"`
+}
+
+type Connection struct {
+	Source    string `json:"source"`
+	Target    string `json:"target"`
+	Label     string `json:"label,omitempty"`
+	Direction string `json:"direction,omitempty"`
+	Protocol  string `json:"protocol,omitempty"`
+	TLS       bool   `json:"tls,omitemity"`
+	Capacity  int    `json:"capacity,omitempty"`
+}
+
+type Design struct {
+	Nodes       []Node `json:"nodes"`
+	Connections []Connection
+}
+
+type Cache struct {
+	Label          string `json:"label"`
+	CacheTTL       int    `json:"cacheTTL"`
+	MaxEntries     int    `json:"maxEntries"`
+	EvictionPolicy string `json:"evictionPolicy"`
+}
+
+type CDN struct {
+	Label           string `json:"label"`
+	TTL             int    `json:"ttl"`
+	GeoReplication  string `json:"geoReplication"`
+	CachingStrategy string `json:"cachingStrategy"`
+	Compression     string `json:"compression"`
+	HTTP2           string `json:"http2"`
+}
+
+type Database struct {
+	Label       string `json:"label"`
+	Replication int    `json:"replication"`
+}
+
+type DataPipeline struct {
+	Label          string `json:"label"`
+	BatchSize      int    `json:"batchSize"`
+	Transformation string `json:"transformation"`
+}
+
+type LoadBalancer struct {
+	Label     string `json:"label"`
+	Algorithm string `json:"algorithm"`
+}
+
+type MessageQueue struct {
+	Label            string `json:"label"`
+	QueueCapacity    int    `json:"queueCapacity"`
+	RetentionSeconds int    `json:"retentionSeconds"`
+}
+
+type Microservice struct {
+	Label           string `json:"label"`
+	InstanceCount   int    `json:"instanceCount"`
+	CPU             int    `json:"cpu"`
+	RAMGb           int    `json:"ramGb"`
+	RPSCapacity     int    `json:"rpsCapacity"`
+	MonthlyUSD      int    `json:"monthlyUsd"`
+	ScalingStrategy string `json:"scalingStrategy"`
+	APIVersion      string `json:"apiVersion"`
+}
+
+type Monitoring struct {
+	Label          string `json:"label"`
+	Tool           string `json:"tool"`
+	AlertMetric    string `json:"alertMetric"`    // e.g., "cpu", "latency"
+	ThresholdValue int    `json:"thresholdValue"` // e.g., 80
+	ThresholdUnit  string `json:"thresholdUnit"`  // e.g., "percent", "ms"
+}
+
+type ThirdPartyService struct {
+	Label    string `json:"label"`
+	Provider string `json:"provider"`
+	Latency  int    `json:"latency"`
+}
+
+type WebServer struct {
+	CPU            int `json:"cpu"`
+	RamGb          int `json:"ramGb"`
+	RPSCapacity    int `json:"rpsCapacity"`
+	MonthlyCostUsd int `json:"monthlyCostUsd"`
+}
+
+func (n *Node) UnmarshalJSON(data []byte) error {
+	type Alias Node // avoid infinite recursion
+	aux := &struct {
+		Props json.RawMessage `json:"props"`
+		*Alias
+	}{
+		Alias: (*Alias)(n),
+	}
+
+	if err := json.Unmarshal(data, aux); err != nil {
+		return err
+	}
+
+	switch n.Type {
+	case "cache":
+		var p Cache
+		if err := json.Unmarshal(aux.Props, &p); err != nil {
+			return err
+		}
+		n.Props = structToMap(p)
+
+	case "cdn":
+		var p CDN
+		if err := json.Unmarshal(aux.Props, &p); err != nil {
+			return err
+		}
+		n.Props = structToMap(p)
+
+	case "database":
+		var p Database
+		if err := json.Unmarshal(aux.Props, &p); err != nil {
+			return err
+		}
+		n.Props = structToMap(p)
+
+	case "data pipeline":
+		var p DataPipeline
+		if err := json.Unmarshal(aux.Props, &p); err != nil {
+			return err
+		}
+		n.Props = structToMap(p)
+
+	case "loadBalancer":
+		var p LoadBalancer
+		if err := json.Unmarshal(aux.Props, &p); err != nil {
+			return err
+		}
+		n.Props = structToMap(p)
+
+	case "messageQueue":
+		var p MessageQueue
+		if err := json.Unmarshal(aux.Props, &p); err != nil {
+			return err
+		}
+		n.Props = structToMap(p)
+
+	case "microservice":
+		var p Microservice
+		if err := json.Unmarshal(aux.Props, &p); err != nil {
+			return err
+		}
+		n.Props = structToMap(p)
+
+	case "monitoring/alerting":
+		var p Monitoring
+		if err := json.Unmarshal(aux.Props, &p); err != nil {
+			return err
+		}
+		n.Props = structToMap(p)
+
+	case "third party service":
+		var p ThirdPartyService
+		if err := json.Unmarshal(aux.Props, &p); err != nil {
+			return err
+		}
+		n.Props = structToMap(p)
+
+	case "webserver":
+		var p WebServer
+		if err := json.Unmarshal(aux.Props, &p); err != nil {
+			return err
+		}
+		n.Props = structToMap(p)
+
+	default:
+		var generic map[string]interface{}
+		if err := json.Unmarshal(aux.Props, &generic); err != nil {
+			return err
+		}
+		n.Props = generic
+	}
+
+	return nil
+}
+
+func structToMap(v interface{}) map[string]interface{} {
+	data, _ := json.Marshal(v)
+	var result map[string]interface{}
+	json.Unmarshal(data, &result)
+	return result
+}
diff --git a/internals/simulation/simulation.go b/internals/design/simulation.go
similarity index 96%
rename from internals/simulation/simulation.go
rename to internals/design/simulation.go
index 290e31f..8a51e48 100644
--- a/internals/simulation/simulation.go
+++ b/internals/design/simulation.go
@@ -56,15 +56,6 @@ type ComponentSpec struct {
 	DbReadReplica   DbReadReplica
 }
 
-type Design struct {
-	NumWebServerSmall     int
-	NumWebServerMedium    int
-	CacheType             CacheType // Enum (see below)
-	CacheTTL              string
-	NumDbReplicas         int
-	PromotionDelaySeconds int
-}
-
 type FailureEvent struct {
 	Type string
 	Time int
diff --git a/internals/level/level.go b/internals/level/level.go
new file mode 100644
index 0000000..e301129
--- /dev/null
+++ b/internals/level/level.go
@@ -0,0 +1,105 @@
+package level
+
+import (
+	"encoding/json"
+	"fmt"
+	"os"
+)
+
+type Level struct {
+	ID          string     `json:"id"`
+	Name        string     `json:"name"`
+	Description string     `json:"description"`
+	Difficulty  Difficulty `json:"difficulty"`
+
+	TargetRPS               int     `json:"targetRps"`
+	DurationSec             int     `json:"durationSec"`
+	MaxMonthlyUSD           int     `json:"maxMonthlyUsd"`
+	MaxP95LatencyMs         int     `json:"maxP95LatencyMs"`
+	RequiredAvailabilityPct float64 `json:"requiredAvailabilityPct"`
+
+	MustInclude           []string       `json:"mustInclude,omitempty"`
+	MustNotInclude        []string       `json:"mustNotInclude,omitempty"`
+	EncouragedComponents  []string       `json:"encouragedComponents,omitempty"`
+	DiscouragedComponents []string       `json:"discouragedComponents,omitempty"`
+	MinReplicas           map[string]int `json:"minReplicas,omitempty"`
+	MaxLatencyPerNodeType map[string]int `json:"maxLatencyPerNodeType,omitempty"`
+	CustomValidators      []string       `json:"customValidators,omitempty"`
+
+	FailureEvents  []FailureEvent     `json:"failureEvents,omitempty"`
+	ScoringWeights map[string]float64 `json:"scoringWeights,omitempty"`
+
+	Hints []string `json:"hints,omitempty"`
+}
+
+type Difficulty string
+
+const (
+	DifficultyEasy   Difficulty = "easy"
+	DifficultyMedium Difficulty = "medium"
+	DifficultyHard   Difficulty = "hard"
+)
+
+var Registry map[string]map[string]Level
+
+type FailureEvent struct {
+	Type     string `json:"type"`
+	TimeSec  int    `json:"timeSec"`
+	TargetID string `json:"targetId,omitempty"`
+}
+
+func LoadLevels(path string) ([]Level, error) {
+	file, err := os.Open(path)
+	if err != nil {
+		return nil, fmt.Errorf("Error opening levels.json: %w", err)
+	}
+	defer file.Close()
+
+	var levels []Level
+	err = json.NewDecoder(file).Decode(&levels)
+	if err != nil {
+		return nil, fmt.Errorf("Error decoding levels.json: %w", err)
+	}
+
+	return levels, nil
+}
+
+func InitRegistry(levels []Level) {
+	Registry = make(map[string]map[string]Level)
+	for _, lvl := range levels {
+		// check if level already exists here
+		if _, ok := Registry[lvl.Name]; !ok {
+			Registry[lvl.Name] = make(map[string]Level)
+		}
+		// populate it
+		Registry[lvl.Name][string(lvl.Difficulty)] = lvl
+	}
+}
+
+func GetLevel(name string, difficulty Difficulty) (*Level, error) {
+	diffMap, ok := Registry[name]
+	if !ok {
+		return nil, fmt.Errorf("level name %s not found", name)
+	}
+
+	lvl, ok := diffMap[string(difficulty)]
+	if !ok {
+		return nil, fmt.Errorf("difficulty %s not available for level '%s'", difficulty, name)
+	}
+	return &lvl, nil
+}
+
+func (d *Difficulty) UnmarshalJSON(b []byte) error {
+	var s string
+	if err := json.Unmarshal(b, &s); err != nil {
+		return err
+	}
+
+	switch s {
+	case string(DifficultyEasy), string(DifficultyMedium), string(DifficultyHard):
+		*d = Difficulty(s)
+		return nil
+	default:
+		return fmt.Errorf("invalid difficulty: %q", s)
+	}
+}