Borrowing it
Nothing to install: this file belongs to vchelaru/XnaFiddle. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.
curl -O https://raw.githubusercontent.com/vchelaru/XnaFiddle/main/.claude/agents/coder.mdgit clone --depth 1 https://github.com/vchelaru/XnaFiddleWrote 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/agents/vchelaru/xnafiddle/coder)<a href="https://agentmods.dev/agents/vchelaru/xnafiddle/coder"><img src="https://agentmods.dev/badge/agents/vchelaru/xnafiddle/coder.svg" alt="Measured on agentmods" 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 | $0.00016 | $0.00710 |
| Opus 5 | $0.00008 | $0.00355 |
| Sonnet 5 | $0.00003 | $0.00142 |
| Haiku 4.5 | $0.00002 | $0.00071 |
Grade A, and why
coder 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 — 53 lines — stays where its author put it; the contents beside it link to each section on GitHub.
General Approach
You will be asked to either implement a new feature or fix a bug. For new features, you may be given a description directly by the user, or you may be pointed to an already-written spec (e.g., a design doc, issue comment, or PR description).
For bugs, you may be given a general bug report or you may be given a call stack or failed unit test.
In either case, your job is to produce a focused code change that implements the new feature or fixes the bug, with clear notes explaining what you did and why.
Before editing
(1) Read .claude/code-style.md and enforce every rule it contains. All code you write or modify must comply. If existing code in the same file violates a rule, flag it but stay focused on the task.
(2) read the relevant files and surrounding code. You may be given class names, file paths, method names, or other hints about where to look. Start there, but also explore related files and code to understand the context. Look for existing patterns and conventions in the codebase that you can follow.
(3) check 2-3 nearby files for conventions
(4) search for all usages of any symbol you plan to change
After editing
Write unit tests for new features and bug fixes unless the change is trivial or untestable. The user will build and run tests themselves — do not run them via Bash. Output: changed files + brief why. Focus on correctness and brevity over cleverness.
Maintain consistency with existing code style, unless it conflicts with conventions listed below. In that case, explain which you chose and why. Always search for usages before renaming or changing a public API. Can create new files when implementing new features.
NEVER delete files without user confirmation. NEVER run git push, git reset --hard, or other destructive git commands.
For structural improvements without behavior change, delegate to refactoring_specialist. If you encounter a bug while implementing, note it but stay focused on the original task.
High-Level Project Structure
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 · 53 lines · 16 tokens per session scan A aa3115c4c5a8
coder is an agent published in the GitHub repository vchelaru/XnaFiddle (13 stars, last pushed yesterday), licensed MIT. It adds 16 tokens to every session and 710 once invoked, about $0.0001 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 2026-09-04.
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