What is writing-st-code?

A local MCP server for testing Chrome extensions from an AI coding agent. It can access extension storage, background service workers, and request-filtering rules.

Use it to inspect or test chrome.storage, Service Workers, and declarative network-request rules.

It gives the agent direct access to extension parts that are otherwise difficult to inspect during testing.

How efranceschetti/festo-codesys-mcp configures Claude Code

Reuse

Borrowing it

Nothing to install: this file belongs to efranceschetti/festo-codesys-mcp. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.

Copy the file

curl -O https://raw.githubusercontent.com/efranceschetti/festo-codesys-mcp/main/.claude/skills/writing-st-code/SKILL.md

Clone the repo

git clone --depth 1 https://github.com/efranceschetti/festo-codesys-mcp

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.

README.md

[![agentmods](https://agentmods.dev/badge/skills/efranceschetti/festo-codesys-mcp/writing-st-code/github.svg)](https://agentmods.dev/skills/efranceschetti/festo-codesys-mcp/writing-st-code)

Your own site

<a href="https://agentmods.dev/skills/efranceschetti/festo-codesys-mcp/writing-st-code"><img src="https://agentmods.dev/badge/skills/efranceschetti/festo-codesys-mcp/writing-st-code/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.

Your own site · 80×15

<a href="https://agentmods.dev/skills/efranceschetti/festo-codesys-mcp/writing-st-code"><img src="https://agentmods.dev/badge/skills/efranceschetti/festo-codesys-mcp/writing-st-code.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 94 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 504 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.

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.

Model	Per session	Once invoked
Fable 5.1	$0.00094	$0.00504
Opus 5.5	$0.00038	$0.00202
Sonnet 5.5	$0.00019	$0.00101
Haiku 4.5	$0.00009	$0.00050

Measured 1mo ago against content hash 3177e53b86e3, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

writing-st-code 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 1mo 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.

.claude/skills/writing-st-code/SKILL.md · 33 lines

What it actually says

Writing Structured Text

Never write ST from memory. Follow this order:

1. Load conventions (once per session)

plc_knowledge action=topic conventions, then abbreviations.
Point lookups while coding: plc_lookup action=hungarian (type -> prefix).

2. Reuse before create

plc_library action=search with keywords from the request (e.g. "motor", "valve", "PID").
Match found -> plc_library action=get, adapt it (rename, adjust IO). Do NOT rewrite from scratch.
No match -> proceed to create. For a new FB also load topic state-machines.

3. Create with the right tool

FB -> create_function_block | cyclic logic -> create_program
ENUM/STRUCT -> create_data_type | globals -> create_gvl
Servo/stepper motion? STOP — that is the motion-control skill (MC_*_Festo blocks, never custom FBs).

4. Verify (mandatory, in order)

review_st_code — naming violations. Fix all.
debug_plc_code — runtime bugs (WHILE loops, missing bErr handling, safety gaps). Fix Criticals.
For a full structured review of a file, delegate to the plc-reviewer subagent.

5. Record in memory

If the code reveals durable project facts (hardware chosen, a new project FB, a design decision), update .claude/memory/ per MEMORY.md rules.

Hard rules: PascalCase + Hungarian, English-only identifiers/comments, FB interface bEnable/bExecute -> bDone/bBusy/bErr/nErrId, nState 0/10-80/90/99. IO access only through GVLs — never hardcode %I/%Q addresses in FBs.

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.

1mo ago First seen · 33 lines · 94 tokens per session scan A 3177e53b86e3

Subscribe to this mod's changes

writing-st-code is a skill published in the GitHub repository efranceschetti/festo-codesys-mcp (2 stars, last pushed 21d ago), licensed MIT. It adds 94 tokens to every session and 504 once invoked, about $0.0004 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 2026-08-31.

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festo-codesys-mcp: Skill for Claude Code