ctf-writeup

ctf-writeup is a skill for Claude Code from ljagiello/ctf-skills. It costs 48 tokens per session (1,136 once invoked), scanned A, original, MIT.

A tool for writing a standard handoff document after solving a CTF, or capture-the-flag cybersecurity challenge. The writeup records the challenge details, solution steps, tools, evidence, and lessons learned.

In plain words
What is it for?
Use it to create a submission-ready Markdown writeup, including the exploit or solve script, challenge metadata, important decisions, and final flag.
Why use it?
It turns scattered commands, scripts, and notes into a reproducible explanation that teammates or competition organizers can check quickly.

Skill for Claude Code

Written for Claude Code: allowed-tools in frontmatter. Also seen: mentions Claude Code.

Good fit Use it to create a submission-ready Markdown writeup, including the exploit or solve script, challenge metadata, important decisions, and final flag.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/ljagiello/ctf-skills/ctf-writeup
About the project

ctf-skills is a collection of agent instructions for solving capture-the-flag security challenges, including web exploitation, binary vulnerabilities, cryptography, reverse engineering, forensics, and OSINT. It is intended for agents and people working through CTF problems, and its skills can be loaded into supported coding-agent workflows.

ljagiello/ctf-skills · 3,549 stars · on GitHub · ljagiello.github.io

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.

Any agent
npx skills add ljagiello/ctf-skills --skill ctf-writeup
Clone the repo
git clone --depth 1 https://github.com/ljagiello/ctf-skills

Made for: Claude Code.

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 ctf-writeup

README.md
[![agentmods](https://agentmods.dev/badge/skills/ljagiello/ctf-skills/ctf-writeup/github.svg)](https://agentmods.dev/skills/ljagiello/ctf-skills/ctf-writeup)
Your own site
<a href="https://agentmods.dev/skills/ljagiello/ctf-skills/ctf-writeup"><img src="https://agentmods.dev/badge/skills/ljagiello/ctf-skills/ctf-writeup/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.

agentmods 80×15 button for ctf-writeup

Your own site · 80×15
<a href="https://agentmods.dev/skills/ljagiello/ctf-skills/ctf-writeup"><img src="https://agentmods.dev/badge/skills/ljagiello/ctf-skills/ctf-writeup.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 48 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,136 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe. Third-party audits
  • Socket pass 27 Oct 2026
  • Snyk pass 27 Oct 2026
  • NVIDIA SkillSpector pass 7 Sept 2026
How audits are shown
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 5.1 $0.00048 $0.01136
Opus 5.5 $0.00019 $0.00454
Sonnet 5.5 $0.00010 $0.00227
Haiku 4.5 $0.00005 $0.00114

Measured yesterday against content hash 09633dc2d75f, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

ctf-writeup 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.

Origin

Copies of this mod

1 near-identical copy found in the catalogue:

ctf-writeup/SKILL.md · 141 lines

How it starts

The opening of the file, as written. The whole thing — 141 lines — stays where its author put it; the contents beside it link to each section on GitHub.

CTF Write-up Generator

Generate a standardized submission-style CTF writeup for a solved challenge.

Default behavior:

  • During an active competition, optimize for speed, clarity, and reproducibility
  • Keep writeups short enough that a teammate or organizer can validate the solve quickly
  • Always produce a submission-style writeup
  • Prefer one complete solve script from challenge data to final flag

Workflow

Step 1: Gather Information

Collect the following from the current session, challenge files, and user input:

  1. Challenge metadata — name, CTF event, category, difficulty, points, flag format
  2. Solution artifacts — exploit scripts, payloads, screenshots, command output
  3. Timeline — key steps taken, dead ends, pivots
# Scan for exploit scripts and artifacts
find . -name '*.py' -o -name '*.sh' -o -name 'exploit*' -o -name 'solve*' | head -20
# Check for flags in output files
grep -rniE '(flag|ctf|eno|htb|pico)\{' . 2>/dev/null

Step 2: Generate Write-up

Write the writeup file as writeup.md (or writeup-<challenge-name>.md) using the submission template below.


Templates

Submission Format

---
title: "<Challenge Name>"
ctf: "<CTF Event Name>"
date: YYYY-MM-DD
category: web|pwn|crypto|reverse|forensics|osint|malware|misc|ai-ml
difficulty: easy|medium|hard
points: <number>
flag_format: "flag{...}"
author: "<your name or team>"
---

# <Challenge Name>

## Summary

<1-2 sentences: what the challenge was and the core technique. Keep it direct.>

## Solution

### Step 1: <Action>

<Explain the key observation in 3-8 short lines. Keep it direct.>

\`\`\`python
<one complete solving script from provided challenge data to printing the final flag>
\`\`\`

### Step 2: <Action> (optional)

<Only add this when a second short step genuinely helps readability, such as separating the core observation from final verification.>

### Step 3: <Action> (optional)

<Use only if the challenge really needs it. Keep the total number of steps small.>

## Flag

\`\`\`
flag{example_flag_here}
\`\`\`

Read the full file on GitHub · 141 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. yesterday Changed · +1 lines 09633dc2d75f
  2. 1mo ago Changed f67169dc8287
  3. 1mo ago First seen · 140 lines · 48 tokens per session scan A e3f43f41e3b4

Subscribe to this mod's changes

ctf-writeup is a skill published in the GitHub repository ljagiello/ctf-skills (3,549 stars, last pushed yesterday), licensed MIT. It adds 48 tokens to every session and 1,136 once invoked, about $0.0002 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.

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