claude-sbox

A Claude Code skill that teaches Claude to write idiomatic s&box code — C# components, Razor UI, physics, and networking — without falling back on Unity patterns.

s&box is Facepunch's Source 2 game engine with a C# scripting layer. Its API, lifecycle, and networking model are nothing like Unity's, which means stock Claude hallucinates constantly: void Start(), GetComponent<T>() in the Unity sense, Physics.Raycast, [SerializeField], StartCoroutine — all wrong in s&box. This skill loads when you're writing s&box code and redirects Claude to the correct APIs, verified against the engine's exported schema.

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Install

Personal (available across all your projects):

mkdir -p ~/.claude/skills
git clone https://github.com/gavogavogavo/claude-sbox ~/.claude/skills/sbox

Project-local (this game only):

cd my-sbox-game
mkdir -p .claude/skills
git clone https://github.com/gavogavogavo/claude-sbox .claude/skills/sbox

Claude Code picks up skill file changes live. However, if ~/.claude/skills/ did not exist when your Claude Code session started (i.e. this is your first personal skill), you need to restart Claude Code after the mkdir so the watcher registers the new directory.

Why the sbox (not claude-sbox) directory name? The name: frontmatter in SKILL.md is sbox, which becomes the /sbox slash command. Cloning into ~/.claude/skills/sbox/ keeps the directory name and the invocation name in sync.

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Verify it's working

In any Claude Code session, type:

/sbox

The router loads. Alternatively, ask a triggering question and watch Claude reach for a reference file:

How do I write a networked player controller in s&box?

Claude should open references/core-concepts.md, references/networking.md, and/or references/patterns-and-examples.md before answering — that's the signal the skill is working. If it answers from memory without reading a file, something's wrong; see Troubleshooting.

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What's inside

SKILL.md is a router, not a reference. When Claude needs detail, it opens one of these:

| File | Lines | Covers | |---|---:|---| | SKILL.md | 271 | Router + Unity→s&box translation table + the ten rules | | references/core-concepts.md | 575 | Scene system, GameObjects, Components, lifecycle, [Property], prefabs, scene events, GameObjectSystem, async | | references/components-builtin.md | 729 | 144 built-in components — renderers, rigidbodies, colliders, CharacterController, CameraComponent, lights, audio, UI, NavMeshAgent, PlayerController, particles, post-processing | | references/ui-razor.md | 834 | Razor panels, SCSS, flexbox layout, built-in controls (Button / TextEntry / DropDown / SliderControl / VirtualGrid), NavigationHost, transitions | | references/networking.md | 672 | Lobbies, Connection, [Sync] + SyncFlags, [Rpc.Broadcast/Host/Owner], ownership, INetworkListener, INetworkSpawn, snapshot data, dedicated servers | | references/input-and-physics.md | 597 | Input system, SceneTrace builder API, PhysicsWorld, collision, Vector3/Rotation/Angles/Transform/BBox/Ray/Capsule, TimeSince/TimeUntil, Gizmo.Draw | | references/api-schema-core.md | 930 | Full public signatures for the ~50 most-used types | | references/api-schema-extended.md | 2753 | Namespace-organized index of 738 additional types for discovery | | references/patterns-and-examples.md | 1056 | 10 complete runnable examples (Health + IDamageable, first-person CharacterController, hitscan weapon, networked game manager, player with [Sync]/RPCs, Razor HUD, rigidbody grenade, NavMeshAgent AI state machine, prefab spawner, trigger pickup) |

Every API signature in every reference file is verified against the s&box engine's exported schema (raw/api-schema.json, ~1,850 types across 61 namespaces). Schema is the single source of truth — if the docs and the schema disagree, the schema wins.

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Updating

cd ~/.claude/skills/sbox
git pull

Claude Code reloads modified skill files within the current session.

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Regenerating from source

End users don't need this. For maintainers who want to rebuild the reference files against a newer s&box engine:

./scripts/fetch-raw.sh         # clones Facepunch/sbox-docs into raw/sbox-docs
# manually place raw/api-schema.json (see docs/DESIGN.md)
node scripts/build_extended.js # rebuilds references/api-schema-extended.md

The full build workflow — including how each reference file was curated, the schema-verification loop, and known gotchas — is documented in docs/DESIGN.md and docs/BUILD_LOG.md.

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Troubleshooting

Claude isn't triggering the skill on s&box questions. Check that the directory is at ~/.claude/skills/sbox/ (not ~/.claude/skills/claude-sbox/ or ~/.claude/skills/sbox-skill/). The directory name must match the name: frontmatter. Also try invoking it explicitly with /sbox to confirm it's installed.

Claude answers s&box questions without opening a reference file. That means it's hallucinating from Unity muscle memory — the exact failure this skill exists to prevent. Either the skill isn't loading, or the description isn't matching. Try /sbox to force-load it, then retry the question.

The skill is loading but suggesting APIs that don't compile. Open an issue with the suggested code and which reference file Claude claims it came from. Every shipped signature should be schema-verified; regressions are bugs.

I cloned it into ~/.claude/skills/claude-sbox/ — now what? Either rename the directory to sbox, or change the name: field in SKILL.md to claude-sbox to match. Same deal for project-local installs.

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Contributing

Issues and PRs welcome. Before submitting:

• Verify new API signatures against raw/api-schema.json. The schema is ground truth. If you can't find a method in the schema, don't add it.
• Keep SKILL.md under 500 lines. It's a router — reference detail lives in references/. If you can answer an s&box question using only SKILL.md without opening a reference file, the router has too much detail.
• Update CHANGELOG.md for any user-visible change.
• Match the existing prose style — terse, dense, written for Claude rather than for a tutorial reader.

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License

MIT — see LICENSE.

This project is not affiliated with or endorsed by Facepunch or Anthropic. s&box is a product of Facepunch Studios. Claude Code and the Agent Skills format are products of Anthropic.