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 JustineDevs/premortem --skill vm-and-bytecode-reversegit clone --depth 1 https://github.com/JustineDevs/premortemWrote 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/justinedevs/premortem/vm-and-bytecode-reverse)<a href="https://agentmods.dev/skills/justinedevs/premortem/vm-and-bytecode-reverse"><img src="https://agentmods.dev/badge/skills/justinedevs/premortem/vm-and-bytecode-reverse/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/justinedevs/premortem/vm-and-bytecode-reverse"><img src="https://agentmods.dev/badge/skills/justinedevs/premortem/vm-and-bytecode-reverse.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 | $0.00042 | $0.04195 |
| Opus 5.5 | $0.00017 | $0.01678 |
| Sonnet 5.5 | $0.00008 | $0.00839 |
| Haiku 4.5 | $0.00004 | $0.00419 |
Grade A, and why
vm-and-bytecode-reverse 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.
This is a copy
100% identical to vm-and-bytecode-reverse — 0 lines differ, which has more behind it and is treated as the original. This page carries a canonical link to it rather than competing with it.
How it starts
The opening of the file, as written. The whole thing — 451 lines — stays where its author put it; the contents beside it link to each section on GitHub.
SKILL: VM & Bytecode Reverse Engineering — Expert Analysis Playbook
AI LOAD INSTRUCTION: Expert techniques for reversing custom virtual machines and bytecode interpreters. Covers dispatcher identification, opcode mapping, custom ISA reconstruction, disassembler/decompiler writing, maze challenges, and real-world VM protector analysis. Base models often fail to recognize the fetch-decode-execute pattern or attempt to analyze VM bytecode as native code.
0. RELATED ROUTING
- code-obfuscation-deobfuscation when the VM is a commercial protector (VMProtect/Themida)
- symbolic-execution-tools when using angr to solve VM-based challenges
- anti-debugging-techniques when the VM includes anti-debug checks
Quick identification
| Binary Pattern | Likely VM Type | Start With |
|---|---|---|
while(1) { switch(bytecode[pc]) } |
Switch-based dispatcher | Map each case to an operation |
Indirect jump via table jmp [table + opcode*8] |
Table-based dispatcher | Dump jump table, analyze handlers |
| Nested if-else chain on byte value | If-chain dispatcher | Same as switch, just different syntax |
| Stack push/pop dominant operations | Stack-based VM | Identify push, pop, arithmetic ops |
reg[X] = ... array operations |
Register-based VM | Map register indices to operations |
| 2D grid + direction input | Maze challenge | Extract grid, apply BFS/DFS |
1. CUSTOM VM IDENTIFICATION
1.1 Structural Indicators
VM Architecture Components:
┌─────────────────────────────────┐
│ Bytecode Program (data section)│
├─────────────────────────────────┤
│ Program Counter (pc/ip) │
│ Register File / Stack │
│ Memory / Data Area │
├─────────────────────────────────┤
│ Dispatcher Loop │
│ ├─ Fetch: opcode = code[pc] │
│ ├─ Decode: lookup handler │
│ └─ Execute: run handler │
└─────────────────────────────────┘
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 · 451 lines · 42 tokens per session scan A 4da387769cea
vm-and-bytecode-reverse is a skill published in the GitHub repository JustineDevs/premortem (2 stars, last pushed 2mo ago), licensed Apache-2.0. It adds 42 tokens to every session and 4,195 once invoked, about $0.0002 per session on Opus 5.5. A static security scan graded it A with 0 findings. It is 100% identical to vm-and-bytecode-reverse, differing in 0 lines, and is treated as a copy.
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