control-ui

Guidance for building or adapting a local browser or desktop-app harness that can control and inspect a user interface.

In plain words
What is it for?
Verifying UI changes, taking screenshots, checking accessibility, reproducing local web or Electron bugs, and collecting logs or performance profiles.
Why use it?
It helps reproduce problems that depend on real focus, keyboard input, scrolling, resizing, or browser rendering, and collect evidence from the running app.

Skill for Claude CodeCodex

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.

agentmods
npx agentmods add skills/tellahq/opensession/control-ui
Any agent
npx skills add tellahq/opensession --skill control-ui
Clone the repo
git clone --depth 1 https://github.com/tellahq/opensession

Made for: Claude Code, Codex.

Per session 49 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,042 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
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 $0.00049 $0.01042
Opus 5 $0.00024 $0.00521
Sonnet 5 $0.00010 $0.00208
Haiku 4.5 $0.00005 $0.00104

Measured 2d ago against content hash 40775510557e, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

control-ui 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 2d 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.

.agents/skills/control-ui/SKILL.md · 114 lines

How it starts

The opening of the file, as written. The whole thing — 114 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Control UI

Use local browser automation to verify UI behavior with evidence. First reuse the repo's own Playwright, browser, or Electron harness if it exists; otherwise assemble a temporary local harness around the app's dev server or Chromium debug port.

What It Is Used For

  • Reproducing UI bugs that depend on real browser focus, keyboard input, scrolling, resizing, or rendering.
  • Verifying visual or accessibility changes with screenshots and snapshots.
  • Checking local web, IDE, or Electron behavior before shipping.
  • Capturing console logs, network logs, CPU profiles, traces, or heap snapshots.
  • Creating before/after evidence for verify-this.

Setup Pattern

  1. Start the app locally using the repo's documented dev command.
  2. Discover existing local harnesses: Playwright tests, Cypress specs, Storybook, browser scripts, Electron launch scripts, or snapshot tools.
  3. For a web app, connect to the local URL with the existing browser tooling.
  4. For Electron/Chromium, enable a remote debugging port when supported.
  5. Select the correct page by stable app markers, not by tab order alone.
  6. Prefer accessibility roles, labels, and stable data-* selectors over coordinates.

Generic Web Harness

Use the repo's installed browser tooling when possible. If the repo already has Playwright, a minimal one-off probe looks like:

import { chromium } from "playwright";

const browser = await chromium.launch();
const page = await browser.newPage({ viewport: { width: 1280, height: 800 } });
await page.goto("http://127.0.0.1:<port>");
await page.getByRole("button", { name: /submit/i }).click();
await page.screenshot({ path: "/tmp/ui-harness-after.png", fullPage: true });
await browser.close();

Do not add Playwright as a project dependency just for this probe unless the user asks. Prefer existing dev dependencies or external browser tools already available in the environment.

Generic CDP Harness

For Electron or a Chromium app launched with --remote-debugging-port=<port>, connect over CDP:

Read the full file on GitHub · 114 lines

Files

What ships with it

2 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.

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. 2d ago First seen · 114 lines · 49 tokens per session scan A 40775510557e

Subscribe to this mod's changes

control-ui is a skill published in the GitHub repository tellahq/opensession (327 stars, last pushed 2d ago), licensed MIT. It adds 49 tokens to every session and 1,042 once invoked, about $0.0002 per session on Opus 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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