B4 is a Linux network packet-processing service that changes network traffic so deep packet inspection systems cannot identify or block its connections. It is used on routers, servers, and desktops to bypass DPI-based blocking, and a router installation can cover devices across the local network. The catalogue lists 12 skills associated with B4.
Borrowing it
Nothing to install: this file belongs to DanielLavrushin/b4. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.
curl -O https://raw.githubusercontent.com/DanielLavrushin/b4/main/.claude/skills/b4-check/SKILL.mdgit clone --depth 1 https://github.com/DanielLavrushin/b4Wrote 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/daniellavrushin/b4/b4-check)<a href="https://agentmods.dev/skills/daniellavrushin/b4/b4-check"><img src="https://agentmods.dev/badge/skills/daniellavrushin/b4/b4-check/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.
<a href="https://agentmods.dev/skills/daniellavrushin/b4/b4-check"><img src="https://agentmods.dev/badge/skills/daniellavrushin/b4/b4-check.svg" alt="Reviewed on agentmods" width="80" 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 5.1 | $0.00129 | $0.01434 |
| Opus 5.5 | $0.00052 | $0.00574 |
| Sonnet 5.5 | $0.00026 | $0.00287 |
| Haiku 4.5 | $0.00013 | $0.00143 |
Grade A, and why
b4-check 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.
The source is not reproduced here
Licensed GPL-3.0
The repository is licensed GPL-3.0, which this catalogue does not treat as permission to reproduce the file. Read it at the source.
What ships with it
5 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.
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 Changed 24b9e7f47854
- 6d ago First seen · 74 lines · 129 tokens per session scan A 48c8133f0eef
b4-check is a skill published in the GitHub repository DanielLavrushin/b4 (1,848 stars, last pushed 4d ago), licensed GPL-3.0. It adds 129 tokens to every session and 1,434 once invoked, about $0.0005 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 2026-10-31.
b4-check compared with skills from other repositories
| Mod | Type | Stars | Last push | Licence | Scan | Tokens | Works with |
|---|---|---|---|---|---|---|---|
| b4-checkDanielLavrushin/b4 | Skill | 1.8k | 4d ago | GPL-3.0 | A | 129 | Claude Code |
| research-engineerdavila7/claude-code-templates | Skill | 33k | today | MIT | A | 43 | Claude Code, Codex |
| tika-eval-compareapache/tika | Skill | 4.1k | yesterday | Apache-2.0 | A | 50 | Claude Code, Codex |
| cua-driverdavidondrej/skills | Skill | 4.3k | 3d ago | MIT | A | 68 | Claude Code, Codex |
| jetson-validate-imageNVIDIA/skills | Skill | 3.9k | yesterday | Apache-2.0 | B | 50 | Claude Code, Codex |
| atmos-validationcloudposse/atmos | Skill | 1.4k | yesterday | Apache-2.0 | A | 31 | Claude Code |
| tddcodewithmukesh/dotnet-claude-kit | Skill | 805 | 2d ago | MIT | A | 81 | Claude Code |