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 julianobarbosa/claude-code-skills --skill justfilegit clone --depth 1 https://github.com/julianobarbosa/claude-code-skillsWrote 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/julianobarbosa/claude-code-skills/justfile)<a href="https://agentmods.dev/skills/julianobarbosa/claude-code-skills/justfile"><img src="https://agentmods.dev/badge/skills/julianobarbosa/claude-code-skills/justfile/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/julianobarbosa/claude-code-skills/justfile"><img src="https://agentmods.dev/badge/skills/julianobarbosa/claude-code-skills/justfile.svg" alt="Reviewed on agentmods" width="80" height="20"></a>- NVIDIA SkillSpector pass
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 | $0.00135 | $0.02390 |
| Opus 5 | $0.00068 | $0.01195 |
| Sonnet 5 | $0.00027 | $0.00478 |
| Haiku 4.5 | $0.00014 | $0.00239 |
Grade A, and why
justfile 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 9d 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 — 152 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Justfile Skill
just is a command runner (not a build system) that saves and runs project-specific commands in a
file called Justfile. It uses make-inspired syntax but is simpler and more portable, with none of
make's idiosyncrasies (.PHONY, tab sensitivity, implicit rules, timestamp tracking).
This skill enforces a consistent house style so every Justfile looks the same across projects.
The rules below are the authoritative convention; Tools/lint.ts validates the deterministic ones.
Workflow Routing
| Trigger | Workflow |
|---|---|
| "create a justfile", "set up just", "add a recipe/module" | Workflows/CreateJustfile.md |
| "migrate Makefile to just", "convert make to just" | Workflows/MigrateFromMake.md |
| "check/lint this justfile", "is this justfile correct" | Workflows/CheckJustfile.md |
When to Use Just vs Make
| Scenario | Tool |
|---|---|
| Project task automation (build, test, deploy, lint) | just |
| Cross-platform command runner | just |
Actual file-based build dependencies (compile .c → .o) |
make |
| Legacy projects already deep in make | make (or migrate) |
Common Mistakes — do NOT do these
Patterns the model often generates incorrectly. Check output against this list.
| WRONG | RIGHT |
|---|---|
justfile (lowercase) |
Justfile (capital J) |
mod docker (bare) |
mod docker '.justfiles/docker.just' |
Module at docker.just or just/docker.just |
Module at .justfiles/docker.just |
default: |
_default: (underscore required) |
@just --list |
@just --list --unsorted (module) or --unsorted --list-submodules (root with modules) |
env("NAME", "val") |
env_var_or_default("NAME", "val") |
| Module file without the three-line header | Every file gets the full header |
Module file without its own _default recipe |
Every file gets its own _default |
Module named after a tool (psql.just) |
Module named after a concern (db.just) |
Tests in docker.just because they run in a container |
Tests in test.just — classify by purpose, not implementation |
| Root recipe duplicates module logic | Root shortcut delegates: build: docker-build |
Ad-hoc names (run-tests, do-lint) |
Standard names: test, lint, build, dev, fmt, check |
Relative paths in module recipes (bash tests/run.sh) |
Use source_directory() for absolute paths |
What ships with it
8 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.
- 9d ago First seen · 152 lines · 135 tokens per session scan A cedb51cebfec
justfile is a skill published in the GitHub repository julianobarbosa/claude-code-skills (10 stars, last pushed 13d ago), licensed MIT. It adds 135 tokens to every session and 2,390 once invoked, about $0.0007 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 2026-08-31.
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