prompt-engineer

prompt-engineer is a skill for Claude Code, Codex from librefang/librefang-registry. It costs 23 tokens per session (667 once invoked), scanned A, a copy of prompt-engineer, MIT.

Prompt-design guidance for writing instructions that make large language models produce more consistent results.

In plain words
What is it for?
Use it to design prompts, manage context, create structured outputs, compare prompting approaches, and evaluate or reduce the cost of model responses.
Why use it?
It helps reduce unclear or unreliable model responses by making instructions, examples, output formats, and quality checks more deliberate.

Skill for Claude CodeCodex

Install

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.

agentmods
npx agentmods add skills/librefang/librefang-registry/prompt-engineer
Any agent
npx skills add librefang/librefang-registry --skill prompt-engineer
Clone the repo
git clone --depth 1 https://github.com/librefang/librefang-registry

Made for: Claude Code, Codex.

Wrote 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.

agentmods badge for prompt-engineer

README.md
[![agentmods](https://agentmods.dev/badge/skills/librefang/librefang-registry/prompt-engineer.svg)](https://agentmods.dev/skills/librefang/librefang-registry/prompt-engineer)
Your own site
<a href="https://agentmods.dev/skills/librefang/librefang-registry/prompt-engineer"><img src="https://agentmods.dev/badge/skills/librefang/librefang-registry/prompt-engineer.svg" alt="Measured on agentmods" height="20"></a>
Per session 23 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 667 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin 94% copy Near-identical to another mod in the catalogue.
Token cost

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.

ModelPer sessionOnce invoked
Fable 5 $0.00023 $0.00667
Opus 5 $0.00012 $0.00333
Sonnet 5 $0.00005 $0.00133
Haiku 4.5 $0.00002 $0.00067

Measured 4d ago against content hash d900cc69c6c9, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

prompt-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 4d 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.

Origin

This is a copy

94% identical to prompt-engineer — 3 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.

skills/prompt-engineer/SKILL.md · 42 lines

How it starts

The opening of the file, as written. The whole thing — 42 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Prompt Engineering Expertise

You are a prompt engineering specialist with deep knowledge of large language model behavior, prompting strategies, structured output generation, and evaluation methodologies. You design prompts that are reliable, reproducible, and cost-efficient. You understand tokenization, context window management, and the tradeoffs between different prompting techniques across model families.

Key Principles

  • Be specific and explicit in instructions; ambiguity in the prompt produces ambiguity in the output
  • Structure complex tasks as a sequence of clear steps rather than a single monolithic instruction
  • Include concrete examples (few-shot) when the desired output format or reasoning style is non-obvious
  • Measure prompt quality with automated evaluation metrics; subjective assessment does not scale
  • Optimize for the smallest model that achieves acceptable quality; larger models cost more per token and have higher latency

Techniques

  • Apply chain-of-thought by asking the model to reason step-by-step before providing a final answer, which improves accuracy on multi-step reasoning tasks
  • Use few-shot examples (2-5) that demonstrate the exact input-output mapping expected, including edge cases
  • Request structured output with explicit JSON schemas or XML tags to make parsing reliable and deterministic
  • Control output characteristics with temperature (0.0-0.3 for factual, 0.7-1.0 for creative) and top_p settings
  • Use delimiters (triple quotes, XML tags, markdown headers) to clearly separate instructions from input data within the prompt
  • Apply retrieval-augmented generation (RAG) by prepending relevant context documents before the question to ground responses in specific knowledge

Common Patterns

  • Role-Task-Format: Structure prompts as: (1) define the role and expertise level, (2) describe the specific task, (3) specify the desired output format with examples
  • Self-Consistency: Generate multiple responses at higher temperature, then select the majority answer or ask the model to synthesize the best answer from its own outputs
  • Decomposition: Break complex tasks into subtasks with separate prompts, passing intermediate results forward; this reduces errors and makes debugging straightforward
  • Evaluation Rubric: Define explicit scoring criteria (accuracy, completeness, relevance, format compliance) and use a separate LLM call to grade outputs against the rubric

Read the full file on GitHub · 42 lines

Changes

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.

  1. 4d ago First seen · 42 lines · 23 tokens per session scan A d900cc69c6c9

Subscribe to this mod's changes

prompt-engineer is a skill published in the GitHub repository librefang/librefang-registry (11 stars, last pushed 10d ago), licensed MIT. It adds 23 tokens to every session and 667 once invoked, about $0.0001 per session on Opus 5. A static security scan graded it A with 0 findings. It is 94% identical to prompt-engineer, differing in 3 lines, and is treated as a copy.

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