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 nlinhvu/learn-java-frameworks-marketplace --skill core-buildergit clone --depth 1 https://github.com/nlinhvu/learn-java-frameworks-marketplaceWrote 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/nlinhvu/learn-java-frameworks-marketplace/core-builder)<a href="https://agentmods.dev/skills/nlinhvu/learn-java-frameworks-marketplace/core-builder"><img src="https://agentmods.dev/badge/skills/nlinhvu/learn-java-frameworks-marketplace/core-builder/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/nlinhvu/learn-java-frameworks-marketplace/core-builder"><img src="https://agentmods.dev/badge/skills/nlinhvu/learn-java-frameworks-marketplace/core-builder.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 | $0.00120 | $0.03704 |
| Opus 5.5 | $0.00048 | $0.01482 |
| Sonnet 5.5 | $0.00024 | $0.00741 |
| Haiku 4.5 | $0.00012 | $0.00370 |
Grade A, and why
core-builder 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 1mo 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 — 307 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Core Builder — Feature Implementation
Philosophy: Integration Point First, Then Build Outward
Each feature starts at its integration point — the exact place where the new feature connects to the existing system. The source project may be in any language (Python, Go, Rust, Node.js, C#, Ruby, Java, etc.) — the output is always simplified Java. The implementation follows the same direction a contributor would: "I see where this feature plugs in, I want to understand what supporting code makes it work, so I trace outward from the integration point."
This produces two artifacts, one truth:
- Working Java code in
src/— compiles, tests pass, is the source of truth - Rich tutorial chapter in
core-docs/— reads back actual source files, never diverges, enriched with ★ Insight blocks and Mermaid diagrams at every design decision
Every integration point choice, simplification decision, technology mapping choice, and design pattern is a teaching moment. The learner doesn't just see WHAT was built — they understand WHY each choice was made, how the source language's idioms were translated to Java, and what alternatives were considered.
MANDATORY: Use Extended Thinking
Use extended thinking before implementing. The quality of the implementation depends on deep upfront reasoning about both the real source project and the simplified Java version. Before writing any code:
- Study the source project's implementation of this feature end-to-end (in whatever language it's written in)
- Identify the integration point — the exact seam where this feature connects to the existing system
- Plan the technology mapping — how source language constructs translate to Java (e.g., goroutines to threads/executors, Python generators to Java iterators, Rust traits to Java interfaces)
- Plan the simplified class mapping — which source types to keep, merge, skip, or hardcode
- Design the build sequence starting from the integration point outward
- Determine what to reuse and extend from prior features
What ships with it
2 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.
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.
- 1mo ago First seen · 307 lines · 120 tokens per session scan A eb95fa4c7d35
core-builder is a skill published in the GitHub repository nlinhvu/learn-java-frameworks-marketplace (20 stars, last pushed 6mo ago), licensed Apache-2.0. It adds 120 tokens to every session and 3,704 once invoked, about $0.0005 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 2026-08-30.
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