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 skills/nrdxp/predicate/engineeringnpx skills add nrdxp/predicate --skill engineeringgit clone --depth 1 https://github.com/nrdxp/predicateWhat 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 | $0.00113 | $0.03289 |
| Opus 5 | $0.00056 | $0.01644 |
| Sonnet 5 | $0.00023 | $0.00658 |
| Haiku 4.5 | $0.00011 | $0.00329 |
Grade A, and why
engineering 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 yesterday.
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 — 297 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Engineering
Always-On Principles
These constraints bind every code edit without skill invocation. They are the standing SWE law promoted into the always-on conditioning layer; deviation requires explicit justification and human approval. Detailed elaboration follows in the By-Moment Reference below.
Root Cause — Never a Band-Aid
A fix that papers over a symptom — a compatibility shim, a workaround that lets a broken design survive, an exception added to silence a warning — is a defect, not a solution. The cause MUST be fixed. If the fix requires more than local changes, HALT and discuss the scope before proceeding; do not re-architect silently.
Compatibility hacks are forbidden. Additions beyond the stated task are forbidden (the Cutting Imperative: do not add features, abstractions, or cleanup not present in the task). When removing code, cut completely — compatibility scaffolding for removed code is entropy that must later be audited for meaning.
No Silent Failures
Every error path MUST be handled or propagated, preserving the causal chain.
Error messages MUST state what failed, why, and where — opaque
messages such as "invalid input" are forbidden. Library code MUST NOT panic; it
MUST return Result/Option to the caller. Application entry points convert
errors to exit codes with clear messages. Secrets, tokens, and PII MUST NOT
appear in logs.
Validate at Boundaries; Trust Internal Invariants
All external inputs MUST be validated at system entry points (user input, API responses, file contents, IPC). Internal call sites MUST NOT add defensive guards against conditions the type system or framework invariants already rule out — that is unnecessary error handling that obscures where the real boundaries are. Validate the perimeter; trust what the perimeter enforced.
Strong Typing — No Escape Hatches
Use the type system to enforce invariants. any, interface{}, or their
language equivalents MUST NOT be used unless genuinely necessary; when used, the
specific reason MUST be documented inline. Library code MUST NOT panic.
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.
- yesterday First seen · 297 lines · 113 tokens per session scan A a99d27d5fea5
engineering is a skill published in the GitHub repository nrdxp/predicate (10 stars, last pushed 8d ago), licensed MIT. It adds 113 tokens to every session and 3,289 once invoked, about $0.0006 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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