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 agentmods add rules/adonai-labs/agent-runway/engineering-principlesgit clone --depth 1 https://github.com/adonai-labs/agent-runwayWrote 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/rules/adonai-labs/agent-runway/engineering-principles)<a href="https://agentmods.dev/rules/adonai-labs/agent-runway/engineering-principles"><img src="https://agentmods.dev/badge/rules/adonai-labs/agent-runway/engineering-principles.svg" alt="Measured on agentmods" 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 | $0.01448 | $0.01448 |
| Opus 5 | $0.00724 | $0.00724 |
| Sonnet 5 | $0.00290 | $0.00290 |
| Haiku 4.5 | $0.00145 | $0.00145 |
Grade A, and why
engineering-principles 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 3d 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 — 200 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Engineering Principles
These principles apply to all code, regardless of language, framework, or layer.
Simplicity first
Write the simplest solution that correctly solves the current problem.
- Do not design for hypothetical futures
- Earn complexity before introducing it
- Every abstraction must isolate real instability or real variation
- If you cannot explain why a layer or pattern exists here, it probably should not
Single reason to change
Each module, class, or function should have one reason to change.
- Group things that change together for the same reason
- Separate things that change for different reasons
- A class that mixes HTTP concerns, business rules, and persistence has too many reasons to change
Naming communicates intent
Names are the primary documentation.
- Name variables, functions, and types for what they represent, not how they are implemented
- Avoid abbreviations, single-letter variables (except loop counters), and generic names (
Manager,Helper,Utils,Servicewithout qualification) - A function named
Processtells nothing;PlaceOrderorValidatePaymentcommunicates intent - If a name needs a comment to explain it, the name is not good enough
Keep files and classes maintainable
Large files are a design smell even when the code still works.
- Prefer files and classes under 600 lines
- Treat 600-800 lines as a warning zone that requires an explicit reason
- Do not create or grow files/classes beyond 800 lines without a strong architectural justification
- Split by responsibility, not by arbitrary line count
- Generated files, migrations, snapshots, lockfiles, and vendor files are exempt
Functions do one thing
- Functions should be short, focused, and at a single level of abstraction
- Extract sub-steps into well-named helper functions rather than layering nested conditionals and logic in one place
- A function doing more than one thing is a candidate for extraction
- Side effects should be obvious from the name and placement
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.
- 3d ago First seen · 200 lines · 1,448 tokens per session scan A 9b19d1d2227b
engineering-principles is a cursor rule published in the GitHub repository adonai-labs/agent-runway (2 stars, last pushed 13d ago), licensed MIT. It adds 1,448 tokens to every session, about $0.0072 per session on Opus 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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