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 agentmods add skills/micheltlutz/dev-challenge/spec-authoringnpx skills add micheltlutz/dev-challenge --skill spec-authoringgit clone --depth 1 https://github.com/micheltlutz/dev-challengeWrote 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/micheltlutz/dev-challenge/spec-authoring)<a href="https://agentmods.dev/skills/micheltlutz/dev-challenge/spec-authoring"><img src="https://agentmods.dev/badge/skills/micheltlutz/dev-challenge/spec-authoring.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 | $0.00083 | $0.01491 |
| Opus 5 | $0.00042 | $0.00745 |
| Sonnet 5 | $0.00017 | $0.00298 |
| Haiku 4.5 | $0.00008 | $0.00149 |
Grade A, and why
spec-authoring 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 5d 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 — 165 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Authoring a spec
For contributors extending the lab. The rule that governs everything here: a spec change and its harness test land in the same pull request, or CI rejects it.
Anatomy
specs/challenges/<track>-<nn>-<slug>/
spec.md frontmatter + objective + contract + requirements
acceptance.md criteria, each with a stable ID
The directory name, the id: in the frontmatter, and the criterion prefix all
have to agree.
Frontmatter
Validated against
specs/schema/challenge.schema.json.
---
id: backend-05-balance # must equal the directory name
title: "Balance (amount)"
track: backend # backend | web | mobile | fullstack
order: 5 # unique within the track
difficulty: intermediate # starter | intermediate | advanced
estimated_hours: 3
depends_on: ["backend-04-statements"] # must exist, must stay acyclic
endpoints: ["GET /balance/"] # must exist in specs/openapi.json
acceptance: acceptance.md
verify: "harness/suites/test_balance.py"
tags: ["auth", "business-rules"]
---
Web and mobile additionally require:
figma_node: "13-5855" # or null
mockups: ["readme_files/images/statement-web.png"]
testids: ["balance-amount", "balance-toggle"] # non-empty
testids is the contract that makes a UI verifiable without dictating a
framework. Choose names that describe the role, not the implementation:
balance-toggle, not eye-icon-button.
Set verifiable: false and verify: null when no automated runner can check
the challenge — the whole mobile track is in that position, and saying so
plainly is better than implying coverage that does not exist.
Writing criteria
### BE05-AC3 — Seeded balance is exact
Given John Doe's token
When GET /balance/
Then `amount` equals 15491.00 within 0.01
- IDs are stable and globally unique.
<PREFIX><nn>-AC<n>:BEback-end,WEBweb,MOBmobile,FSfullstack. Never renumber an existing criterion — append. - One observable behaviour per criterion. If you need "and" in the Then, you probably have two.
- Testable from outside. The harness is black-box. "The code is well structured" is not a criterion; "the response contains no password field" is.
- Say the number.
15491.00, not "the correct balance".
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.
- 5d ago First seen · 165 lines · 83 tokens per session scan A f709d926013b
spec-authoring is a skill published in the GitHub repository micheltlutz/dev-challenge (32 stars, last pushed 3d ago), licensed MIT. It adds 83 tokens to every session and 1,491 once invoked, about $0.0004 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 2026-08-30.
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