---
title: Entities
description: The core data types in Cortex — Agents, Skills, Traits, Behaviors, Personas, Runs, and more.
---

All Cortex entities embed the `cortex.Entity` base type and carry a TypeID identifier. This page provides an overview of every entity and how they relate.

## Base entity

```go
type Entity struct {
    CreatedAt time.Time `json:"created_at"`
    UpdatedAt time.Time `json:"updated_at"`
}
```

Every entity struct embeds `cortex.Entity` to get automatic timestamp tracking.

## Entity overview

### Agent Config

The top-level entity. An agent can operate in **flat mode** (system prompt + tools list) or **persona mode** (referencing a Persona for its identity).

```go
type Config struct {
    cortex.Entity
    ID              id.AgentID
    Name            string
    Description     string
    AppID           string
    SystemPrompt    string         // flat mode
    Model           string
    Tools           []string       // flat mode
    MaxSteps        int
    MaxTokens       int
    Temperature     float64
    PersonaRef      string         // persona mode
    InlineSkills    []string       // persona mode (inline)
    InlineTraits    []string
    InlineBehaviors []string
    Enabled         bool
}
```

### Skill

Defines what an agent **can do**. Bundles tools, knowledge sources, and system prompt fragments. See [Skills](/docs/cortex/human-model/skills).

### Trait

Defines who an agent **is**. Personality dimensions on bipolar axes that influence runtime parameters. See [Traits](/docs/cortex/human-model/traits).

### Behavior

Defines what an agent **does habitually**. Condition-triggered action patterns. See [Behaviors](/docs/cortex/human-model/behaviors).

### Persona

The composition entity that brings everything together. See [Personas](/docs/cortex/human-model/personas).

### Run, Step, ToolCall

Execution entities that record an agent's reasoning process:

- **Run** — A single execution of an agent with 6 lifecycle states
- **Step** — One reasoning step within a run
- **ToolCall** — A tool invocation within a step

See [Runs](/docs/cortex/execution/runs).

### Message

A conversation message with role, content, and timestamp. See [Memory](/docs/cortex/execution/memory).

### Checkpoint

A point where a run pauses for human approval. See [Checkpoints](/docs/cortex/execution/checkpoints).

## Entity relationship diagram

```
Persona
  ├── SkillAssignment[] ──→ Skill
  │                           └── ToolBinding[]
  │                           └── KnowledgeRef[]
  ├── TraitAssignment[] ──→ Trait
  │                           └── Dimension[]
  │                           └── Influence[]
  ├── Behavior[]         ──→ Behavior
  │                           └── Trigger[]
  │                           └── Action[]
  ├── CognitiveStyle
  ├── CommunicationStyle
  └── Perception

Agent Config
  ├── PersonaRef ──→ Persona (persona mode)
  ├── SystemPrompt + Tools (flat mode)
  └── Run[]
        ├── Step[]
        │     └── ToolCall[]
        ├── Checkpoint[]
        └── Message[] (via Memory)
```

## Store interfaces

Each entity type defines its own store interface. These are composed into the single `store.Store` composite:

```go
type Store interface {
    agent.Store      // Create, Get, GetByName, Update, Delete, List
    skill.Store      // CreateSkill, GetSkill, GetSkillByName, ...
    trait.Store      // CreateTrait, GetTrait, GetTraitByName, ...
    behavior.Store   // CreateBehavior, GetBehavior, ...
    persona.Store    // CreatePersona, GetPersona, ...
    run.Store        // CreateRun, GetRun, UpdateRun, ListRuns, ...
    memory.Store     // SaveConversation, LoadConversation, ...
    checkpoint.Store // CreateCheckpoint, GetCheckpoint, ...

    Migrate(ctx context.Context) error
    Ping(ctx context.Context) error
    Close() error
}
```