ZERO DAY

Your terminal is your weapon. Your rig is your character sheet.
Your operating system is your class.

A single-player hacking simulation where you build your rig, choose your OS, and breach procedurally generated networks using real methodology — all through a fully diegetic CRT terminal interface.

$ Game Pillars

Five design principles govern every system in ZERO DAY. No feature ships unless it serves at least one pillar.

• 01
  Accessible Depth — Three tiers of realism let anyone play. A script kiddie sees guided prompts; an APT operator sees raw protocol. The simulation underneath is identical.
• 02
  Authentic Methodology — Real cybersecurity methodology as core gameplay: reconnaissance, scanning, enumeration, exploitation, privilege escalation, and post-exploitation. Every tool and workflow reflects actual practice.
• 03
  Agency Through Systems — Interconnected systems create emergent strategy. Hardware, heat, economy, factions, and contracts interact in ways the player discovers, not ways the designer prescribes.
• 04
  The Interface Is The Game — No menus floating over the game world. The CRT terminal is your entire interface. Seven mood states drive atmosphere through the shader alone — no HUD icons, no alert popups.
• 05
  Progression Crosses Thresholds — Tier advancement is a shift in working depth, not a power increase. Everything the player does at T3, the machine was already doing at T1 on their instruction. Advancing means taking the controls.

$ How to Play

The Core Loop

ZERO DAY operates on three nested loops that create its gameplay rhythm:

Getting Started

When you boot ZERO DAY for the first time:

1. Choose your OS — each has a distinct visual identity and gameplay modifiers. LinuxForge is a solid default; PhantomBSD rewards stealth play.
2. Choose your tier — start at Tier 1 (Script Kiddie) if you're new to hacking games. You can switch tiers at any time.
3. Type help to see available commands. Type man <command> for detailed usage on any command.
4. Type contracts to browse the BBS board. View a contract with contracts <number>. Accept one with contracts accept <number>.
5. Complete the contract — scan, connect, exploit, extract. Monitor your heat throughout.
6. Get paid, upgrade, repeat. Use upgrade to browse hardware. Use rig to see your current setup.

The CRT Experience

There are no menus. There is no HUD. The CRT shader reacts to gameplay through seven distinct mood states:

$ Tier System

Tiers control abstraction depth, not difficulty. The simulation engine is identical at every tier. Tier determines how information is presented and how much the system does on your behalf. Switch freely at any time.

$ Operating Systems

Six operating systems, each with a distinct philosophy, visual identity, and gameplay personality. Your OS choice affects your phosphor palette (CRT color theme), window manager style, starting hardware, and gameplay modifiers.

Phosphor Palettes

Each OS defines 10 semantic color keys that control the CRT visual identity:

$ Hardware & Rig

Your hardware is your character sheet. Six slots, three upgrade tiers each. Every component creates real mechanical constraints that shape your approach. Hardware upgrades are purchased from the market — gated by contracts_completed, not by tier.

$ Commands

ZERO DAY ships with 106 verb commands across fourteen categories. Every command has a base_heat cost (noise generated) and base_ticks cost (time consumed). Type help for a full listing or man <command> for detailed usage.

$ Contracts

Contracts are jobs posted to an anonymous BBS (Bulletin Board System). Each contract is posted by a faction handle, has a risk level, payout, time limit, and one to four objectives. ZERO DAY ships with 45 contracts spanning all four factions and three risk levels.

Contract Lifecycle

AVAILABLE → ACCEPTED → ACTIVE → PENDING_EXTRACT → COMPLETE
                                             |
                                    FAILED / ABANDONED

You can only run one active contract at a time. Completed contracts are appended to your permanent history.

Objective Types

Grading

Contracts grade you on three dimensions: stealth (low heat at completion), speed (ticks used vs. time limit), and precision (clean execution). Your approach matters as much as your success — a sloppy victory pays less than a clean one.

Risk Levels

Procedural Networks

Every target network is procedurally generated with guaranteed solvability — at least two viable attack vectors exist for every objective. Networks have active defenses: intrusion detection systems, sysadmin AI that learns your patterns, firewalls that adapt, and honeypots that trap the careless.

$ CVE Catalog

ZERO DAY features a fictional vulnerability catalog using the ZD-YYYY-NNNN identifier format. Every exploitable service in the game maps to one or more catalog entries, each with a severity score, affected versions, and exploit requirements.

Catalog Entry Structure

Players discover vulnerabilities through scan (finds affected services), cross-reference them with the catalog using exploit --list, and target specific entries with exploit ZD-YYYY-NNNN. At T3, players can chain vulnerabilities for multi-stage attacks.

Exploit Resolution

When a player targets a vulnerability, the engine evaluates: Does the target run the affected service? Is the version in range? Does the player meet the tier and tool requirements? Success probability factors in the player's rig, OS modifiers, and the target's patch level — a fully patched host is immune.

$ Heat & OpSec

Every action generates noise. Every tool leaves traces. The Heat system creates constant tension between getting the job done and staying invisible.

Multi-Dimensional Heat

Heat is tracked on two independent dimensions. Each action specifies which dimension it affects:

Both dimensions use the same 0–100 scale and band system. Some actions affect BOTH dimensions. Detection triggers when either dimension enters the HIGH band — a stealthy network approach means nothing if you leave forensic evidence everywhere.

Heat Bands

Heat sources: every command has a base_heat value. Aggressive actions (exploits, brute-force) generate more heat. Passive actions (ls, cat, pwd) generate less. Your OS may modify heat generation — PhantomBSD generates 25% less, LinuxForge 10% less.

Heat scope: tracked per contract. Completing a contract resets heat, but residual_heat can carry over based on how sloppy the exit was.

Decay: heat decays passively on every tick-advancing command, but the rate depends on your current band. Higher heat = slower decay. Use scrub to reduce network heat by cleaning traces, and use forensic tools to manage host heat.

Idle Heat & Alert Fatigue

Inactive sessions still generate small amounts of heat — open connections are detectable. Extended idle time in a high-security network triggers sysadmin patrol checks. Conversely, defenders suffer alert fatigue: sustained medium-heat activity can cause IDS operators to lower their guard, slightly reducing detection sensitivity over time.

Surveillance Countermeasures

High-security targets deploy active surveillance: traffic analysis, behavioral profiling, and honeypot networks. Counter-surveillance commands let you detect and evade these measures — but counter-surveillance itself generates heat.

$ Forensic Evidence

Every action you take on a target system can leave forensic evidence — artifacts that persist after you disconnect. Evidence accumulates independently of heat and can be discovered during incident response, potentially leading to contract failure or law enforcement attention even after a successful extraction.

Evidence Types

Clean extraction matters. Use scrub for log cleanup, carefully remove tools you deployed, and avoid leaving persistence mechanisms behind unless the contract requires it. A clean post-exploitation phase reduces your evidence footprint and improves contract grades.

$ Law Enforcement

Sloppy operations attract attention beyond the target's defenders. The Law Enforcement Pressure system tracks cumulative evidence across contracts. Get traced too many times or leave too much evidence, and you'll face escalating consequences.

Pressure Levels

Pressure decays slowly over time through clean operations. Lying low, completing stealth contracts, and doing work for Cold Iron (security contractors) can actively reduce pressure. The scrub and evidence management commands are your primary tools for keeping the heat off.

$ Economy

Credits (CR) are earned from contracts and spent on hardware upgrades. The economy uses an append-only transaction ledger — every income and expense is permanently recorded.

Use wallet to check your balance. The market is gated by contracts_completed, not tier. Better hardware requires finishing more jobs.

Cryptocurrency

Some contracts pay in cryptocurrency instead of (or in addition to) credits. Crypto earnings are stored in a separate wallet with its own volatility mechanics — the exchange rate fluctuates based on in-game market conditions.

$ Cloud Resources

The 2039 internet runs on consolidated cloud infrastructure. Cloud targets represent high-value contract objectives with their own attack surface, distinct from traditional on-premise networks.

Cloud Providers (In-Game)

Software Tools

Cloud CLIs and infrastructure tools must be installed before use. Use install <tool> to download and configure tools to your rig. Each tool consumes storage space and some require minimum hardware tiers.

$ Player Scripting

At T3, players unlock the scripting runtime — the ability to write and execute automation scripts that chain commands together. Scripts are stored on your rig's local storage and executed via the script command.

Capabilities

Scripts are stored as plaintext on your rig's STORAGE — storage capacity limits how many scripts you can carry. Use ls ~/scripts to manage them.

$ Assessment & Proctor Mode

ZERO DAY includes a built-in proctored assessment system for cybersecurity education. Instructors run a proctor dashboard that connects to student game instances over a local network, enabling real-time monitoring, controlled lab environments, and automated grading.

How It Works

Assessment Scenarios

Six built-in scenarios cover core cybersecurity skills. Each defines objectives, time limits, and grading weight distribution.

4-Axis Grading

Every assessment is graded on four dimensions, each weighted per scenario:

Letter grades: A ≥ 90%, B ≥ 80%, C ≥ 70%, D ≥ 60%, F < 60%.

Instructor Controls

$ New Game Plus

After completing the main progression, NG+ unlocks a second cycle with retuned difficulty. Your credits, faction reputation, and hardware carry over — but contracts hit harder, network defenses scale up, and heat thresholds tighten.

$ Accessibility

ZERO DAY is a text-heavy game — accessibility is not an afterthought. The following features are built in from day one:

All accessibility settings persist across sessions independently of game saves.

$ Localization

ZERO DAY ships with 6 languages. All UI screens use the translation system — no hardcoded user-facing strings.

$ Factions

Four factions operate in the underground, each with their own philosophy, contract style, and moral boundaries. Building reputation with a faction unlocks better contracts and deeper narrative threads.

$ World Timeline

The year is 2039. The internet you knew is gone. Cloud consolidation, government surveillance acts, and corporate monopolies have reshaped the digital landscape. The underground is the last free space — and it's under siege.

$ Modding Guide

ZERO DAY supports a comprehensive addon system that lets modders add, extend, and override nearly every content type in the game. Addons are data-driven — most modifications require only JSON files, with optional GDScript for custom command logic.

Directory Structure

user://addons/
  my_custom_addon/
    addon.json          # Required manifest
    commands/           # Custom verb definitions
      recon_tool.json
      recon_tool.gd     # Optional: custom executor
    contracts/          # Custom contracts
    factions/           # New or extended factions
    hardware/           # New hardware components
    os/                 # New operating systems
    narrative/          # Story fragments
    music/              # Music tracks (tracks.json)
    shell/              # Shell presets (presets.json)
    cves/               # Custom vulnerability catalog entries
    tools/              # Custom software tools

Operations: Add, Extend, Override

Every content type supports up to three operations:

Load Order & Priority

1. Core game content loads first. This is the baseline.
2. Addon extensions apply in load_order sequence (lower numbers first).
3. First override wins. If two addons override the same content, the lower load_order takes priority.

$ Manifest Schema

Every addon requires an addon.json manifest at its root:

{
  "id": "my_recon_pack",              // Unique identifier (snake_case)
  "name": "Recon Tool Pack",            // Human-readable display name
  "version": "1.0.0",                  // SemVer version
  "author": "YourName",                 // Author or team
  "description": "Adds recon tools",     // Short description
  "game_version_min": "1.0.0",          // Minimum game version required
  "dependencies": [],                    // Other addon IDs this depends on
  "load_order": 100,                     // Lower = loads earlier (default: 100)
  "content": {                            // Maps content types to directories
    "commands":   "commands/",
    "contracts":  "contracts/",
    "factions":   "factions/",
    "hardware":   "hardware/",
    "narrative":  "narrative/",
    "music":      "music/",
    "shell":      "shell/",
    "cves":       "cves/",
    "tools":      "tools/"
  }
}

$ Modding: Commands

Add new terminal commands, extend existing ones with new flags or subcommands, or fully override a built-in command.

Adding a New Command

Create a JSON verb definition in your addon's commands/ directory:

// commands/port_knock.json
{
  "verb_id": "port_knock",
  "signature": "port_knock <host> <ports...>",
  "base_heat": 2,
  "base_ticks": 1,
  "widget_kind": "text_output",
  "intent_template": "Knock on ports {ports} at {host}",
  "execute_key": "port_knock",
  "presentation_tier": 2,
  "description": "Send a port knock sequence to open filtered services"
}

Register it in your manifest:

"content": {
  "commands": {
    "add": [
      { "file": "commands/port_knock.json" }
    ]
  }
}

Custom Command Logic (GDScript)

For commands that need custom behavior beyond the standard pipeline, place a GDScript executor alongside the JSON:

# commands/port_knock.gd
extends VerbExecutor

func execute(args: Dictionary, context: CommandContext) -> VerbResult:
    var host := args.get("host", "") as String
    var ports := args.get("ports", []) as Array
    # Custom logic here
    return VerbResult.success("Knocked: %s" % [", ".join(ports)])

Data-Only Commands (Aliases)

Simple aliases need no GDScript — use alias_target:

{
  "verb_id": "nk",
  "alias_target": "port_knock",
  "description": "Shorthand for port_knock"
}

Extending Existing Commands

"commands": {
  "extend": [
    {
      "verb_id": "scan",
      "add_flags": ["--stealth", "--deep"],
      "add_subcommands": ["vuln"]
    }
  ]
}

Overriding Commands

"commands": {
  "override": [
    {
      "verb_id": "scan",
      "file": "commands/custom_scan.json"
    }
  ]
}

$ Modding: Contracts

Add new contracts with custom network topologies, extend existing contracts, or override them.

Adding a Contract

{
  "id": "custom_heist_01",
  "title": "The Vault Job",
  "poster_handle": "silkthread",
  "briefing": "Meridian needs corporate R&D data. Hardened internal network. Get in, get files, get out clean.",
  "risk_level": "HIGH",
  "base_payout": 8000,
  "time_limit_ticks": 200,
  "target_security_level": 3,
  "faction_tag": "meridian_group",
  "objectives": [
    {
      "type": "FILE_EXFILTRATE",
      "target_file": "/data/research/project_alpha.db",
      "description": "Extract Project Alpha database"
    },
    {
      "type": "SESSION_ESTABLISH",
      "target_host": "10.0.1.50",
      "description": "Persistent access to backup server"
    }
  ],
  "network": {
    "topology": "star",
    "hosts": [
      { "ip": "10.0.1.1", "role": "gateway", "services": ["ssh", "http"] },
      { "ip": "10.0.1.10", "role": "workstation", "services": ["smb"] },
      { "ip": "10.0.1.50", "role": "server", "services": ["ssh", "ftp", "postgres"] }
    ]
  }
}

Extending Contracts

"contracts": {
  "extend": [
    {
      "id": "existing_contract_id",
      "patch": {
        "briefing": "Updated briefing text...",
        "add_objectives": [
          { "type": "CUSTOM_CONDITION", "description": "Leave no logs" }
        ],
        "add_hosts": [
          { "ip": "10.0.1.99", "role": "honeypot" }
        ]
      }
    }
  ]
}

$ Modding: Factions

Add entirely new factions, extend existing ones, or override (warned — affects narrative coherence).

Adding a Faction

{
  "faction_id": "neon_circuit",
  "display_name": "Neon Circuit",
  "type": "hacktivist",
  "description": "Digital artists turned hacktivists. Code is art, art is resistance.",
  "handle": "pixel_prophet",
  "rivals": ["meridian_group"],
  "allies": ["signal_collective"],
  "contract_style": "Digital art installations on corporate networks",
  "will_not_do": ["Destroy creative works", "Target independent artists"]
}

Extending a Faction

"factions": {
  "extend": [
    {
      "faction_id": "signal_collective",
      "add_rivals": ["neon_circuit"]
    }
  ]
}

$ Modding: Hardware

Add new hardware components to any of the six slots, extend existing components, or override.

Adding Hardware

{
  "component_id": "quantum_nic",
  "slot": "NIC",
  "tier": 4,
  "display_name": "Quantum NIC",
  "price": 15000,
  "effects": {
    "scan_depth": 4,
    "scan_speed_multiplier": 0.5
  },
  "prerequisites": {
    "contracts_completed": 30
  },
  "description": "Quantum-entangled network interface. Sees everything."
}

Extending Hardware

"hardware": {
  "extend": [
    {
      "component_id": "gpu_3",
      "add_effects": { "hash_rate_bonus": 0.5 },
      "add_prerequisites": { "faction_rep_undermarket": 50 }
    }
  ]
}

$ Modding: Operating Systems

Add entirely new operating systems with custom phosphor palettes, window manager models, starting hardware, and gameplay modifiers.

Adding an OS

{
  "os_id": "iron_os",
  "display_name": "IronOS",
  "shorthand": "IRON",
  "tagline": "Forged in fire",
  "dominant_phosphor": "red",
  "wm_model": "TILING",
  "phosphor_palette": {
    "bg": "#0a0000",
    "fg_primary": "#ff4040",
    "fg_secondary": "#cc3030",
    "accent": "#ff6020",
    "border": "#401010",
    "selection": "#602020",
    "comment": "#804040",
    "alert_low": "#ff8040",
    "alert_mid": "#ff4020",
    "alert_high": "#ff0000"
  },
  "starting_hardware": {
    "CPU": 1, "RAM": 1, "NIC": 1,
    "STORAGE": 1, "GPU": 2, "COOLING": 1
  },
  "gameplay_modifiers": {
    "heat_multiplier": 1.1,
    "cpu_speed_bonus": 0.9
  }
}

All 10 palette keys are required when adding a new OS. When extending, provide only the keys you're changing.

Extending an OS

"os": {
  "extend": [
    {
      "os_id": "linux_forge",
      "patch_palette": { "accent": "#40ff80" },
      "patch_modifiers": { "heat_multiplier": 0.85 }
    }
  ]
}

$ Modding: CVE Catalog

Add custom fictional vulnerabilities to the game's CVE catalog. All entries must use the ZD- prefix — entries without it are rejected at load time.

Adding a Vulnerability

{
  "zd_id": "ZD-2039-1001",
  "title": "QuantumDB Authentication Bypass",
  "severity": 9.1,
  "affected_service": "quantumdb",
  "affected_versions": "2.0.0-2.4.3",
  "exploit_type": "auth_bypass",
  "requires_auth": false,
  "tier_minimum": 2,
  "description": "Malformed auth token causes QuantumDB to skip credential verification."
}

Extending Existing CVEs

"cves": {
  "extend": [
    {
      "zd_id": "ZD-2038-0042",
      "patch": {
        "affected_versions": "1.0.0-3.2.1",
        "severity": 9.8
      }
    }
  ]
}

$ Modding: Software Tools

Add custom installable software tools that players can download to their rig. Tools are required by certain commands (especially cloud operations) and consume rig storage.

Adding a Tool

{
  "id": "quantum_scanner",
  "display_name": "QuantumScan",
  "description": "Advanced vulnerability scanner with quantum-accelerated pattern matching",
  "size_kb": 128,
  "required_by": ["qscan"],
  "tier_minimum": 2,
  "install_ticks": 5
}

Extending Existing Tools

"tools": {
  "extend": [
    {
      "id": "aws_cli",
      "patch": {
        "size_kb": 96,
        "required_by": ["aws", "s3cmd"]
      }
    }
  ]
}

$ Modding: Narrative

Add narrative fragments that appear as discoverable content during gameplay, each with unlock conditions.

Adding Narrative

{
  "fragment_id": "iron_lore_01",
  "title": "The Forge Master's Log",
  "content": "Day 47. The compiler is sentient. I'm sure of it now...",
  "tags": ["lore", "iron_os", "ai"],
  "unlock_conditions": {
    "contracts_completed": 10,
    "os_id": "iron_os"
  }
}

Extending Narrative

"narrative": {
  "extend": [
    {
      "fragment_id": "existing_fragment",
      "add_content": "Additional paragraph appended...",
      "add_tags": ["conspiracy"]
    }
  ]
}

$ Modding: Music

ZERO DAY uses a 3-intensity-layer music system powered by Ovani. Every track has a main layer (always audible), an intensity_1 layer (fades in during tense moments), and an intensity_2 layer (fades in at critical heat). Layers crossfade automatically based on the game's mood system — modders provide raw audio files and metadata only.

Declare "music": "music/" in your addon manifest's content map. Inside that directory, create a tracks.json file — a JSON array of track definitions.

Track Schema

Intensities Mode (Default)

The layers object maps layer names to .ogg or .wav file paths relative to the music directory:

Example: tracks.json

// music/tracks.json
[
  {
    "id": "sample_ambient",
    "display_name": "Sample Ambient Track",
    "reverb_tail": 4.0,
    "mode": "intensities",
    "layers": {
      "main": "base_drone.ogg",
      "intensity_1": "tension.ogg",
      "intensity_2": "critical.ogg"
    }
  },
  {
    "id": "lofi_loop",
    "display_name": "Lo-Fi Loop",
    "mode": "loop30",
    "file": "lofi_30s.ogg"
  }
]

$ Modding: Shell Presets

Customize the terminal with shell presets that define command aliases and environment variables. Declare "shell": "shell/" in your addon manifest's content map, then create a presets.json file.

Example: presets.json

// shell/presets.json
{
  "extends": "default",
  "aliases": {
    "ll": "ls -la",
    "cls": "clear",
    "ports": "scan --ports"
  },
  "variables": {
    "EDITOR": "nano"
  }
}

extends inherits from the named base preset ("default" gives you all built-in aliases). Aliases expand at parse time — typing ll runs ls -la. Variables are available to commands via the shell environment.

$ Advanced Modding

Complete Addon Example

A full addon that adds a new faction, commands, contracts, custom vulnerabilities, tools, music, and shell aliases:

// addon.json
{
  "id": "neon_circuit_pack",
  "name": "Neon Circuit Faction Pack",
  "version": "1.0.0",
  "author": "ExampleModder",
  "description": "Adds Neon Circuit faction with custom contracts and tools",
  "game_version_min": "1.0.0",
  "content": {
    "commands": "commands/",
    "factions": "factions/",
    "contracts": "contracts/",
    "cves": "cves/",
    "tools": "tools/",
    "music": "music/",
    "shell": "shell/"
  }
}

Content Type Support Matrix

Best Practices

• Prefer add over override. New content creates no conflicts. Overrides can collide.
• Use extend for small changes. Adjusting a price or adding a flag is cleaner than a full override.
• Set load_order thoughtfully. Default is 100. Content packs: 100–200. Total conversions: 900+.
• Prefix your IDs. Use neon_circuit_art_bomb not art_bomb to avoid collisions.
• Respect faction will_not_do constraints when adding contracts for existing factions.
• Follow the existing price/effect curve for hardware. Proportional improvement, not exponential.
• Include a README in your addon directory with install instructions and known incompatibilities.
• Test alongside core content. Your addon should enhance, not break, the base game.

ZERO DAY — A hacking simulation by Sojo

106 commands · 45 contracts · 6 operating systems · 18 hardware components · 6 languages · 11 moddable content types