preflight

preflight is a skill for Claude Code, Codex from haabe/mycelium. It costs 18 tokens per session (1,211 once invoked), scanned A, original, MIT.

A pre-work checklist for delivery tasks. It checks limits such as available time, people, quality level, dependencies, and whether the work is a demo or production change.

In plain words
What is it for?
Use it before implementation or follow-up work to record constraints, estimate effort, and decide when to reduce or reconfirm the scope.
Why use it?
It prevents a plan from being larger than the available budget and prompts a new scope decision when unexpected work grows.

Skill for Claude CodeCodex

Part of the mycelium plugin — 54 skills, 6 hooks shipped together

Install

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.

agentmods
npx agentmods add skills/haabe/mycelium/preflight
Any agent
npx skills add haabe/mycelium --skill preflight
Clone the repo
git clone --depth 1 https://github.com/haabe/mycelium

Made for: Claude Code, Codex.

Or install mycelium, the plugin that ships this one along with the rest of its 54 skills, 6 hooks.

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.

agentmods badge for preflight

README.md
[![agentmods](https://agentmods.dev/badge/skills/haabe/mycelium/preflight.svg)](https://agentmods.dev/skills/haabe/mycelium/preflight)
Your own site
<a href="https://agentmods.dev/skills/haabe/mycelium/preflight"><img src="https://agentmods.dev/badge/skills/haabe/mycelium/preflight.svg" alt="Measured on agentmods" height="20"></a>
Per session 18 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,211 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
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.

ModelPer sessionOnce invoked
Fable 5 $0.00018 $0.01211
Opus 5 $0.00009 $0.00606
Sonnet 5 $0.00004 $0.00242
Haiku 4.5 $0.00002 $0.00121

Measured 3d ago against content hash dcf3abc4b9a0, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

preflight 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.

plugins/mycelium/skills/preflight/SKILL.md · 112 lines

How it starts

The opening of the file, as written. The whole thing — 112 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Preflight Skill

Pre-delivery validation checklist. Run before every implementation task.

Checklist

Constraints (ALWAYS FIRST)

Before scoping any delivery work, establish constraints. Do not propose a plan before knowing the budget.

  • Time budget: "How much time do you have for this?" (hours, days, sprint length)
  • Resource constraints: Solo? Team? What skills are available?
  • Fidelity: Demo/prototype vs. production? Who is the audience?
  • Dependencies: Waiting on anything external?

If time budget < 8 hours, scope aggressively — one vertical slice, no polish. If the initial plan exceeds the time budget, cut scope before presenting it to the user.

Re-forecast trigger (audit-triggered / emergent work). Work that opens as "just address the recommendations", "quick fix", or any audit/assessment follow-up still gets a constraint pass — set an explicit estimate even when no one asked for one. Then, mid-session, re-forecast when the work crosses ~2× the estimate or when no estimate was ever set: stop, state actual-so-far vs estimate, and re-scope or re-confirm the budget before continuing. The failure this catches: emergent cycles that bypass preflight and balloon silently (dogfood cycle-history.yml — a "~2h" audit cycle ran ~9h; a "session-scope" one ran ~14h). The re-forecast becomes the calibration.effort_accuracy data point at /retrospective.

Source: Hoskins transcript (2026-04-25) — agent proposed 20-hour plan before learning user had 8 hours. Goldratt (Theory of Constraints — identify the constraint before optimizing). Corrections.md: "Over-scope before constraints." Re-forecast trigger from the 2026-06-15 /framework-health effort-calibration finding (audit-triggered cycles balloon past estimate).

Context

  • corrections.md reviewed for relevant past mistakes
  • patterns.md reviewed for applicable patterns
  • Current diamond phase is Develop or Deliver
  • Acceptance criteria are clear and measurable
  • Scenarios linked: .claude/canvas/scenarios.yml has scenarios for this solution, and acceptance criteria trace back to scenario success/failure states (Hoskins)

Read the full file on GitHub · 112 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.

  1. 3d ago First seen · 112 lines · 18 tokens per session scan A dcf3abc4b9a0

Subscribe to this mod's changes

preflight is a skill published in the GitHub repository haabe/mycelium (45 stars, last pushed 3d ago), licensed MIT. It adds 18 tokens to every session and 1,211 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 2026-08-30.

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