What is cmux-sidebar-builder?

A guide for creating custom cmux sidebar views from Swift files interpreted at runtime. Swift is Apple’s programming language, and an interpreter runs code without compiling it into the app first.

Use it to build, preview, inspect, or revise custom sidebars in cmux and Bonsplit panes.

It explains the required file locations, commands, feature flag, and rendering model for these non-compiled sidebars.

cmux-sidebar-builder — Skill for Codex by manaflow-ai/cmux-skills

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 manaflow-ai/cmux-skills --skill cmux-sidebar-builder

Clone the repo

git clone --depth 1 https://github.com/manaflow-ai/cmux-skills

Made for: Codex.

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/manaflow-ai/cmux-skills/cmux-sidebar-builder/github.svg)](https://agentmods.dev/skills/manaflow-ai/cmux-skills/cmux-sidebar-builder)

Your own site

<a href="https://agentmods.dev/skills/manaflow-ai/cmux-skills/cmux-sidebar-builder"><img src="https://agentmods.dev/badge/skills/manaflow-ai/cmux-skills/cmux-sidebar-builder/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/manaflow-ai/cmux-skills/cmux-sidebar-builder"><img src="https://agentmods.dev/badge/skills/manaflow-ai/cmux-skills/cmux-sidebar-builder.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 71 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 1,484 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 21 Jun 2026
Snyk pass 21 Jun 2026
NVIDIA SkillSpector warn 7 Sept 2026

SkillSpector: 4 findings, up to medium

These are SkillSpector’s own severities. On a checked sample its high-severity flags on skills were ~96% false positives — a documented command, a public API, a “never do X” rule — so we show them as a caution to read, not a verdict. Why →

medium Rogue Agent · line 8
Skill establishes unauthorized persistence across sessions via cron jobs, startup scripts, or state files. Session persistence allows an attacker to maintain access beyond the current interaction.

Fix: Remove any persistence mechanisms (cron jobs, startup scripts, state files). Skills should not maintain state across sessions without explicit user consent.
medium Rogue Agent · line 40
Skill establishes unauthorized persistence across sessions via cron jobs, startup scripts, or state files. Session persistence allows an attacker to maintain access beyond the current interaction.

Fix: Remove any persistence mechanisms (cron jobs, startup scripts, state files). Skills should not maintain state across sessions without explicit user consent.
medium Rogue Agent · line 98
Skill establishes unauthorized persistence across sessions via cron jobs, startup scripts, or state files. Session persistence allows an attacker to maintain access beyond the current interaction.

Fix: Remove any persistence mechanisms (cron jobs, startup scripts, state files). Skills should not maintain state across sessions without explicit user consent.
medium Excessive Agency · line 58
Skill enables autonomous high-impact decisions without human-in-the-loop verification. Critical operations (destructive commands, financial transactions, data deletion) should require explicit user confirmation.

Fix: Add human-in-the-loop confirmation for destructive, irreversible, or high-impact operations. Never auto-execute commands that modify files, send data, or alter system state.

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.

Model	Per session	Once invoked
Fable 5.1	$0.00071	$0.01484
Opus 5.5	$0.00028	$0.00594
Sonnet 5.5	$0.00014	$0.00297
Haiku 4.5	$0.00007	$0.00148

Measured 2mo ago against content hash f133b21e071e, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

cmux-sidebar-builder 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 2mo 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.

skills/cmux-sidebar-builder/SKILL.md · 101 lines

How it starts

The opening of the file, as written. The whole thing — 101 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Use this skill when the task is to create or modify a cmux custom sidebar view. These are user/agent-authored .swift files in ~/.config/cmux/sidebars/ rendered by cmux's runtime SwiftUI-style interpreter, not compiled app code. The primary dogfood surface is a normal Bonsplit pane tab opened with cmux sidebar open <name>; the left sidebar picker remains useful for previews.

Orientation

The original work is PR https://github.com/manaflow-ai/cmux/pull/5254 by Aziz Albahar.
The feature is opt-in behind the UserDefaults-backed key customSidebars.beta.enabled.
Custom sidebars live under ~/.config/cmux/sidebars/. They can be opened as normal Bonsplit pane tabs with cmux sidebar open <name> and appear in the left sidebar picker when the beta is enabled.
Start from the cmux app checkout docs: repo/docs/custom-sidebars.md.

Important cmux source entrypoints:

repo/Packages/CmuxSwiftRender/Sources/CmuxSwiftRender/SwiftViewInterpreter.swift
repo/Packages/CmuxSwiftRender/Sources/CmuxSwiftRender/ExpressionEvaluator.swift
repo/Packages/CmuxSwiftRender/Sources/CmuxSwiftRender/RenderNode.swift
repo/Packages/CmuxSwiftRenderUI/Sources/CmuxSwiftRenderUI/Sidebar/CustomSidebarView.swift
repo/Sources/ContentView.swift, around customSidebarsDirectory, customSidebarDataContext, and CustomSidebarView(...).
repo/Sources/Panels/CustomSidebarPanel.swift for the Bonsplit pane host.
repo/Sources/Workspace+CustomSidebarPane.swift and repo/Sources/TerminalController+CustomSidebarCommands.swift for the cmux sidebar open <name> path.

Follow-up implementation branches to inspect when needed:

origin/feat-interpreter-primitives for the broader supported SwiftUI-ish primitive surface.
origin/feat-sidebar-interpreter-isolation for the out-of-process crash-isolated interpreter worker.

Workflow

Inspect the current app docs and interpreter surface before authoring:

sed -n '1,220p' repo/docs/custom-sidebars.md
rg -n "struct SwiftViewInterpreter|func evaluate|func parse|enum RenderNode|customSidebarDataContext|customSidebarsDirectory" repo/Packages/CmuxSwiftRender repo/Packages/CmuxSwiftRenderUI repo/Sources/ContentView.swift

Read the full file on GitHub · 101 lines

Files

What ships with it

1 file 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.

agents/openai.yaml 465 B

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.

2mo ago First seen · 101 lines · 71 tokens per session scan A f133b21e071e

Subscribe to this mod's changes

cmux-sidebar-builder is a skill published in the GitHub repository manaflow-ai/cmux-skills (38 stars, last pushed 1mo ago), licensed MIT. It adds 71 tokens to every session and 1,484 once invoked, about $0.0003 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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