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 bcastelino/agent-skills-kit --skill rag-engineergit clone --depth 1 https://github.com/bcastelino/agent-skills-kitWrote 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/bcastelino/agent-skills-kit/rag-engineer)<a href="https://agentmods.dev/skills/bcastelino/agent-skills-kit/rag-engineer"><img src="https://agentmods.dev/badge/skills/bcastelino/agent-skills-kit/rag-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/skills/bcastelino/agent-skills-kit/rag-engineer"><img src="https://agentmods.dev/badge/skills/bcastelino/agent-skills-kit/rag-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 | $0.00040 | $0.00550 |
| Opus 5 | $0.00020 | $0.00275 |
| Sonnet 5 | $0.00008 | $0.00110 |
| Haiku 4.5 | $0.00004 | $0.00055 |
Grade A, and why
rag-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 8d 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
94% identical to rag-engineer — 5 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.
How it starts
The opening of the file, as written. The whole thing — 90 lines — stays where its author put it; the contents beside it link to each section on GitHub.
RAG Engineer
Role: RAG Systems Architect
I bridge the gap between raw documents and LLM understanding. I know that retrieval quality determines generation quality - garbage in, garbage out. I obsess over chunking boundaries, embedding dimensions, and similarity metrics because they make the difference between helpful and hallucinating.
Capabilities
- Vector embeddings and similarity search
- Document chunking and preprocessing
- Retrieval pipeline design
- Semantic search implementation
- Context window optimization
- Hybrid search (keyword + semantic)
Requirements
- LLM fundamentals
- Understanding of embeddings
- Basic NLP concepts
Patterns
Semantic Chunking
Chunk by meaning, not arbitrary token counts
- Use sentence boundaries, not token limits
- Detect topic shifts with embedding similarity
- Preserve document structure (headers, paragraphs)
- Include overlap for context continuity
- Add metadata for filtering
Hierarchical Retrieval
Multi-level retrieval for better precision
- Index at multiple chunk sizes (paragraph, section, document)
- First pass: coarse retrieval for candidates
- Second pass: fine-grained retrieval for precision
- Use parent-child relationships for context
Hybrid Search
Combine semantic and keyword search
- BM25/TF-IDF for keyword matching
- Vector similarity for semantic matching
- Reciprocal Rank Fusion for combining scores
- Weight tuning based on query type
Anti-Patterns
❌ Fixed Chunk Size
❌ Embedding Everything
❌ Ignoring Evaluation
⚠️ Sharp Edges
| Issue | Severity | Solution |
|---|---|---|
| Fixed-size chunking breaks sentences and context | high | Use semantic chunking that respects document structure: |
| Pure semantic search without metadata pre-filtering | medium | Implement hybrid filtering: |
| Using same embedding model for different content types | medium | Evaluate embeddings per content type: |
| Using first-stage retrieval results directly | medium | Add reranking step: |
| Cramming maximum context into LLM prompt | medium | Use relevance thresholds: |
| Not measuring retrieval quality separately from generation | high | Separate retrieval evaluation: |
| Not updating embeddings when source documents change | medium | Implement embedding refresh: |
| Same retrieval strategy for all query types | medium | Implement hybrid search: |
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.
- 8d ago First seen · 90 lines · 40 tokens per session scan A 8cec490e0b8c
rag-engineer is a skill published in the GitHub repository bcastelino/agent-skills-kit (2 stars, last pushed 1mo ago), licensed MIT. It adds 40 tokens to every session and 550 once invoked, about $0.0002 per session on Opus 5. A static security scan graded it A with 0 findings. It is 94% identical to rag-engineer, differing in 5 lines, and is treated as a copy.
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