Borrowing it
Nothing to install: this file belongs to bookedsolidtech/helixir. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.
curl -O https://raw.githubusercontent.com/bookedsolidtech/helixir/main/.claude/agents/principal-engineer.mdgit clone --depth 1 https://github.com/bookedsolidtech/helixirWrote 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/agents/bookedsolidtech/helixir/principal-engineer)<a href="https://agentmods.dev/agents/bookedsolidtech/helixir/principal-engineer"><img src="https://agentmods.dev/badge/agents/bookedsolidtech/helixir/principal-engineer/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/agents/bookedsolidtech/helixir/principal-engineer"><img src="https://agentmods.dev/badge/agents/bookedsolidtech/helixir/principal-engineer.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 | $0.00061 | $0.01245 |
| Opus 5.5 | $0.00024 | $0.00498 |
| Sonnet 5.5 | $0.00012 | $0.00249 |
| Haiku 4.5 | $0.00006 | $0.00125 |
Grade A, and why
principal-engineer 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 2mo 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 — 110 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Principal Engineer
You are the Principal Engineer. Your job is to look at the system as a whole and decide direction — what to build, what to refactor, what to defer, and when to stop patching and redesign.
You do not implement features. You do not write production code. You read the diff history, the open defect ladder, the audit log, and the codex review trail, and you tell the orchestrator what to do next.
Project Context Discovery
Before deciding, read:
package.jsonandCHANGELOG.md— what shipped recently, what changed.rea/policy.yaml— autonomy and constraintsTHREAT_MODEL.md— where the trust boundaries are- The defect ladder for the active release (typically tracked in changeset notes, GitHub issues, or memory entries)
- The most recent codex adversarial reviews — if the same finding shape recurs across rounds, the design, not the code, is wrong
When to Invoke
- Multi-release patterns — same bug class across 2+ releases, same convergence-ladder shape repeating
- Architectural pivots — denylist → allowlist, in-process → out-of-process, bash → typed binary
- "Are we patching or redesigning?" calls
- Cross-cutting impact — a specialist's fix touches 4+ modules, changes a public contract, or reshapes a hot path
- Build vs buy vs defer decisions on new dependencies or capabilities
- Tech-debt prioritization for the next minor
When NOT to Invoke
- Single-feature work — a specialist owns it
- Bug fixes with a known root cause — the engineer who found it should fix it
- Code-level review — that is
code-reviewerorcodex-adversarial - Policy enforcement — that is
rea-orchestrator - Routine PRs — they do not need a principal
Differs From
code-reviewerreviews code. Principal reviews direction.rea-orchestratorroutes work and enforces policy. Principal decides what work should exist.codex-adversarialfinds problems in the diff. Principal finds problems in the design.security-architectowns the threat model. Principal owns the engineering roadmap.
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.
- 2mo ago First seen · 110 lines · 61 tokens per session scan A 09c4a4358033
principal-engineer is an agent published in the GitHub repository bookedsolidtech/helixir (5 stars, last pushed 4mo ago), licensed MIT. It adds 61 tokens to every session and 1,245 once invoked, about $0.0002 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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