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 vvedantb/eva --skill principle-make-operations-idempotentgit clone --depth 1 https://github.com/vvedantb/evaWrote 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/vvedantb/eva/principle-make-operations-idempotent)<a href="https://agentmods.dev/skills/vvedantb/eva/principle-make-operations-idempotent"><img src="https://agentmods.dev/badge/skills/vvedantb/eva/principle-make-operations-idempotent/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/vvedantb/eva/principle-make-operations-idempotent"><img src="https://agentmods.dev/badge/skills/vvedantb/eva/principle-make-operations-idempotent.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 | $0.00046 | $0.00315 |
| Opus 5.5 | $0.00018 | $0.00126 |
| Sonnet 5.5 | $0.00009 | $0.00063 |
| Haiku 4.5 | $0.00005 | $0.00032 |
Grade A, and why
principle-make-operations-idempotent 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 11d 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
89% identical to principle-make-operations-idempotent — 13 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.
What it actually says
Make Operations Idempotent
Design operations so they converge to the correct state regardless of how many times they run or where they start from. Every state-mutating operation should answer: "What happens if this runs twice? What happens if the previous run crashed halfway?"
Why: Commands, lifecycle operations, and processing loops run where crashes, restarts, and retries are normal. If partial state changes the next run's outcome, every restart becomes a debugging session.
The pattern:
- Convergent startup: scan for existing state, clean stale artifacts, adopt live sessions
- Content-based cleanup: compare by content equivalence, not creation order
- Self-healing locks: use PID-based stale lock detection
- Idempotent scheduling: failed work respawns cleanly, fresh input regenerated after each cycle
The test:
- What happens if this runs twice in a row?
- What happens if the previous run crashed at every possible point?
- Does re-execution converge to the same end state?
If any answer is "it depends on what state was left behind," the operation needs a reconciliation step.
Adapted from pstack (MIT, Copyright (c) 2026 Lauren Tan).
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.
- 11d ago First seen · 26 lines · 46 tokens per session scan A 91bc3d234d26
principle-make-operations-idempotent is a skill published in the GitHub repository vvedantb/eva (101 stars, last pushed today), licensed MIT. It adds 46 tokens to every session and 315 once invoked, about $0.0002 per session on Opus 5.5. A static security scan graded it A with 0 findings. It is 89% identical to principle-make-operations-idempotent, differing in 13 lines, and is treated as a copy.
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