Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx skills add LichAmnesia/unreal-engine-agent-skills --skill ue5-deterministic-sim-testsgit clone --depth 1 https://github.com/LichAmnesia/unreal-engine-agent-skillsWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/lichamnesia/unreal-engine-agent-skills/ue5-deterministic-sim-tests)<a href="https://agentmods.dev/skills/lichamnesia/unreal-engine-agent-skills/ue5-deterministic-sim-tests"><img src="https://agentmods.dev/badge/skills/lichamnesia/unreal-engine-agent-skills/ue5-deterministic-sim-tests/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/skills/lichamnesia/unreal-engine-agent-skills/ue5-deterministic-sim-tests"><img src="https://agentmods.dev/badge/skills/lichamnesia/unreal-engine-agent-skills/ue5-deterministic-sim-tests.svg" alt="Reviewed on agentmods" width="80" height="20"></a>What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00138 | $0.01454 |
| Opus 5.5 | $0.00055 | $0.00582 |
| Sonnet 5.5 | $0.00028 | $0.00291 |
| Haiku 4.5 | $0.00014 | $0.00145 |
Grade A, and why
ue5-deterministic-sim-tests scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 1mo ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
How it starts
The opening of the file, as written. The whole thing — 103 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Deterministic Simulation and Evidence
"The code is written" is not evidence. Neither is "it compiles", "it looks right", or a screenshot of the editor. For agent-driven development this matters more than usual, because the agent cannot see the game and the human is not watching every run.
The cheapest evidence in a vehicle-combat game is a seeded headless match: run twenty full AI matches in seconds, with no rendering, and assert every one terminated with a legal winner. That single test catches AI stalls, unclosable endgames, scoring bugs, and match-flow regressions at once — and it costs nothing to re-run on every change.
Establish the determinism contract first
Determinism is not a feature you add later. It is a set of constraints you either adopt at the start or pay dearly to retrofit.
- Fixed logic timestep. Gameplay state advances on a fixed step, accumulated from real
time. Rendering interpolates. Anything gameplay-authoritative that integrates with a
variable
DeltaTimeis non-deterministic by construction. - Seeded streams, one per subsystem, all derived from a single match seed. Never a global
RNG. See
references/determinism-rules.md. - No gameplay reads from presentation. Physics-driven visual motion, particle state, and animation must not influence outcomes. This is the rule that makes headless running possible at all.
- No frame-rate-dependent smoothing in gameplay code — time constants, never per-frame lerp factors.
- Iteration order must be stable. Iterating a hash map whose order varies between runs silently breaks determinism in a way that is very hard to find.
- Simulation must link without rendering. Enforced by module boundaries — see
ue5-project-context. - Decide the tolerance. Bit-exact is achievable if you are careful with floating point; "same winner, same seed" is much cheaper and usually sufficient. Pick one and state it, because it determines how strict every assertion must be.
What ships with it
4 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 1mo ago First seen · 103 lines · 138 tokens per session scan A 3d6802aec5c2
ue5-deterministic-sim-tests is a skill published in the GitHub repository LichAmnesia/unreal-engine-agent-skills (5 stars, last pushed 2mo ago), licensed MIT. It adds 138 tokens to every session and 1,454 once invoked, about $0.0006 per session on Opus 5.5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.
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