What is jac copilot-instructions.md?

Project-specific instructions for AI coding assistants working on Jac, a programming language and its compiler, runtime, and tools. The repository is a monorepo, meaning one repository contains several related parts and packages.

Use them when changing the Jac compiler, runtime, language server, documentation, integrations, or related scripts, and when running the project's tests or checks.

They provide the repository layout and the approved commands for building, testing, formatting, and checking changes, so work follows the project's process.

How jaseci-labs/jac configures GitHub Copilot

Reuse

Borrowing it

Nothing to install: this file belongs to jaseci-labs/jac. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.

Copy the file

curl -O https://raw.githubusercontent.com/jaseci-labs/jac/main/.github/copilot-instructions.md

Clone the repo

git clone --depth 1 https://github.com/jaseci-labs/jac

Made for: GitHub Copilot.

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.

README.md

[![agentmods](https://agentmods.dev/badge/instructions/jaseci-labs/jac/copilot-instructions/github.svg)](https://agentmods.dev/instructions/jaseci-labs/jac/copilot-instructions)

Your own site

<a href="https://agentmods.dev/instructions/jaseci-labs/jac/copilot-instructions"><img src="https://agentmods.dev/badge/instructions/jaseci-labs/jac/copilot-instructions/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.

Your own site · 80×15

<a href="https://agentmods.dev/instructions/jaseci-labs/jac/copilot-instructions"><img src="https://agentmods.dev/badge/instructions/jaseci-labs/jac/copilot-instructions.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 637 This file is loaded in full into every session.

When invoked 637 The same file — it is already loaded in full.

Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.

Origin original No closer match found 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.

Model	Per session	Once invoked
Fable 5.1	$0.00637	$0.00637
Opus 5.5	$0.00255	$0.00255
Sonnet 5.5	$0.00127	$0.00127
Haiku 4.5	$0.00064	$0.00064

Measured 3d ago against content hash d9674dcfd3bf, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

jac copilot-instructions.md 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 3d 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.

.github/copilot-instructions.md · 78 lines

How it starts

The opening of the file, as written. The whole thing — 78 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Copilot Instructions

Repository Structure

This monorepo contains:

jac/: Jac language compiler, runtime, language server, and the client/desktop runtimes (jac/jaclang/client/)
jac-byllm/: LLM integration and model-driven features
docs/: Documentation site and reference materials
scripts/: Build, test, and maintenance scripts

Common Workflows

jaclang ships as the single jac binary (a Jac launcher + the bundled JacPython runtime) -- there is no pip-installed jaclang. Build it and put it on PATH with ./scripts/fresh_env.sh (see CONTRIBUTING.md).

Run tests through the binary's bundled runner (JAC_TEST_JOBS=auto runs them in parallel):

cd jac && JAC_TEST_JOBS=auto jac test tests

Run the formatting/lint gate (same checks the git hook runs):

jac precommit

Package-Specific Notes

jac/ (Compiler & Runtime)

Grammar: jac/jaclang/compiler/jac.lark
IR: unitree.py (UniTree nodes)
Passes: jac/jaclang/compiler/passes/
Codegen: jcir_gen_pass.jac, jcir_bc_gen_pass.jac
Compiler passes subclass Transform/UniPass with enter_*/exit_* hooks
Test fixtures: jac/jaclang/compiler/**/tests/fixtures/
For type system work, see .github/agents/type-system-agent.md

jac-byllm/ (LLM Features)

Core logic: byllm/lib.py, llm_connector.py
Schema definitions: schema.py
Examples: examples/agentic_ai/

Client & Desktop Runtimes

Now part of jaclang core: jac/jaclang/client/

Jac Language Conventions

Import syntax:

import from module { symbol, another_symbol }
import module as alias;

Entry point:

with entry { /* ... */ }

PR Guidelines

Target repository: Always create PRs against https://github.com/jaseci-labs/jaseci (not forks). Use gh pr create --repo jaseci-labs/jaseci.
Release notes: If your PR affects Jac developer experience, add a release-note fragment at release_notes/unreleased/<package>/<PR#>.<category>.md.
Grouping: Organize related changes under sections like "Type Checking Enhancements" or "Cloud Platform Updates".
Testing: Ensure relevant tests pass before submitting.

Read the full file on GitHub · 78 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.

3d ago Changed · +2 tokens per session d9674dcfd3bf
2mo ago First seen · 78 lines · 635 tokens per session scan A 28b3757d98aa

Subscribe to this mod's changes

jac copilot-instructions.md is an instructions file published in the GitHub repository jaseci-labs/jac (953 stars, last pushed yesterday), licensed MIT. It adds 637 tokens to every session, about $0.0025 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.

jac copilot-instructions.md next to 6 instructions from other repositories
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jac copilot-instructions.mdjaseci-labs/jac	Instructions file	953	yesterday	MIT	A	637	GitHub Copilot
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vscode oss-third-party-notices.instructions.mdmicrosoft/vscode	Instructions file	195k	yesterday	MIT	A	5,516	GitHub Copilot
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deepseek-harness AGENTS.mddeepseek-ai/deepseek-harness	Instructions file	274k	2d ago	MIT	A	4,313	Codex, OpenCode

jac: Instructions file for GitHub Copilot