Guide · Agent skill
How to use the CTF File Parser Chain agent skill
Updated · written with AI from the project's own documentation and checked against our catalogue data
The CTF File Parser Chain skill (competition-file-parser-chain) is a specialist instruction set that tells an AI agent how to follow one uploaded or imported file through every step that processes it, from ingress to the final backend effect. It is written for security students and penetration testers working on capture-the-flag challenges or authorised lab applications. After this guide you will know what the skill does, how to install it, how to phrase requests so it triggers, and what limits to respect.
CTF File Parser Chainzhaoxuya520/reverse-skill · MIT Download the skill Quick start
- 1Download the ZIP. Download the skill ZIP from this page and keep it somewhere you can find it.
- 2Install the parent skill. Make sure $ctf-sandbox-orchestrator is installed and active before using this skill.
- 3Unzip into the skills folder. Unzip into ~/.claude/skills/ for personal use or into a project's .claude/skills/ folder for one project.
- 4Or upload in the Claude apps. Go to Settings → Capabilities → Skills and upload the ZIP if you use the Claude apps.
- 5Ask a specific file question. Describe the upload or import path and the question, such as where a file goes after extraction.
- 6Review the mapped chain. Check each boundary, derived artifact and parser choice in the answer before drawing conclusions.
What the skill makes the agent do
The skill focuses on the hard part of file-handling challenges: following a file through archive extraction, format conversion, previews, parser calls and deserialization. The agent maps each step in order, keeps the original upload and every derived file labelled separately, and records filenames, MIME guesses, extensions, temp paths and parser choices before changing anything.
It then reduces the path to the smallest sequence that produces a notable backend effect, written as upload, derived artifact, parser boundary, resulting effect. The skill also asks the agent to separate what the client-side validation checks from what the backend parser actually does.
- Maps ingress, temp storage, extraction, conversion, parser call, deserialization and final consumer in order
- Keeps original and derived files separate
- Identifies whether the weakness sits in archive handling, MIME inference, file conversion, path resolution or deserialization
- Produces one minimal replayable file-processing sequence
Install the skill (ZIP or Claude apps upload)
Download the ZIP from this page. To install it for your user account, unzip it into ~/.claude/skills/. To install it for a single project, unzip it into that project's .claude/skills/ folder. Alternatively, upload the ZIP in the Claude apps under Settings → Capabilities → Skills.
The package contains agents/openai.yaml, references/file-parser-chain.md and SKILL.md. Check that SKILL.md is present after unzipping, since the agent reads its instructions from that file.
- Personal install: unzip into ~/.claude/skills/
- Project install: unzip into the project's .claude/skills/
- Apps install: Settings → Capabilities → Skills, then upload the ZIP
~/.claude/skills/Install the parent skill first
This skill is a downstream add-on. It only applies after the parent skill $ctf-sandbox-orchestrator is installed, active and has set the sandbox assumptions. If the parent is missing, the skill tells the agent to return to the orchestrator first, so install and activate it before you rely on this one.
- Parent skill $ctf-sandbox-orchestrator must be installed and active
- You need access to the sandboxed challenge environment and its files
How to trigger it with natural requests
The skill is meant to activate when you ask about how an upload or import is handled. Describe the file path and the question you want answered. Mention the sandboxed challenge context so the agent starts from the orchestrator's assumptions.
Good requests name a specific artifact and a specific question, such as where a file goes after upload or which parser reads it. Vague requests about general security are less likely to match the skill's purpose.
- "In the sandbox challenge, trace what happens to the uploaded archive after extraction."
- "Explain how this imported file reaches the deserializer and what the backend does with it."
- "Check whether the preview converter changes the file type before the parser runs."
- "Connect this uploaded artifact to the decisive backend effect."
Read the output and keep the evidence together
The agent's answer should list each boundary in order, with the original file and every derivative named separately. Look for the exact point where backend behaviour differs from what the user interface shows. The skill asks the agent to keep ingress details, parser details and effect details together so the chain can be replayed.
Replies are written in Simplified Chinese unless you explicitly ask for English, so say so in your request if you need English output.
- Ingress: request, filename, MIME, temp path, storage key
- Parser: tool or library, branch condition, derived artifact
- Effect: rendered output, parsed object, backend branch or worker task
Safety notes: scripts and network
According to the package description, this skill runs no scripts and uses no network. It is a set of written instructions. It is aimed at sandboxed competition targets, and the skill does not check scope itself, so you are responsible for testing only systems you are authorised to test.
Do not use it against live production systems or third-party services without written authorisation. Do not use it standalone; it is marked internal and expects the parent orchestrator to be active.
- Runs scripts: no
- Uses network: no
- Use only on sandboxed or authorised lab targets
- The skill does not verify scope; you must
What people use it for
- Tracing how an uploaded archive is extracted and where its members land in temp storage
- Explaining whether a preview or format converter changes a file before a parser reads it
- Following an imported file to a deserializer and identifying the backend branch it triggers
- Reducing a multi-step upload challenge to one minimal replayable sequence for a write-up
Frequently asked questions
How do I install the CTF File Parser Chain skill?
Download the ZIP from this page and unzip it into ~/.claude/skills/ for personal use, or into a project's .claude/skills/ folder. You can also upload the ZIP in the Claude apps under Settings → Capabilities → Skills.
Do I need another skill installed first?
Yes. The skill is a downstream add-on that requires the parent skill $ctf-sandbox-orchestrator to be installed and active, with sandbox assumptions already set. Without it, the skill tells the agent to return to the orchestrator first.
Does this skill run scripts or use the internet?
According to the package details, it runs no scripts and uses no network. It consists of written instructions and reference notes that the agent follows.
Is this skill free to use?
The source material given here states the licence as MIT but does not list prices, so check the licence file in the package for the terms that apply.
Can I use it on a live website?
No. It is aimed at sandboxed competition targets and authorised lab applications. Do not use it on live production systems or third-party services without written authorisation, because the skill does not check scope itself.
Why does the agent answer in Chinese?
The SKILL.md instructs the agent to reply in Simplified Chinese unless the user explicitly asks for English. Say you want English in your request to change this.
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Our verdict
This skill suits security students and penetration testers who work on CTF challenges or authorised lab apps involving file uploads and deserialization, and who want a structured way to trace a file through each parser boundary. It is a poor fit for anyone wanting a standalone tool, a general web scanner, or work on live systems, since it is internal, depends on its parent orchestrator skill, and does not verify scope.
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