CARBON

CARBON Core — free, open-source AI testing for your coding agent

Your AI test manager agent. Jay examines your project and changes, prioritizes risk, coordinates software testing and turns findings into visual evidence. Use CARBON Core for QA, bug finding, accessibility testing, regression-test planning and evidence-backed quality reports. Free under the MIT license.

Start with `/carbon:carbon` in Claude or `/carbon` in Codex. Watch a compact execution plan, the current check and recorded screenshots as the investigation progresses. Reports distinguish executed tests, proposed work and untested gaps.

Website and guide · Command reference · Download releases · Codex edition · Report an issue

The product name is CARBON Core. The repository and technical plugin name remain carbon-free and carbon so existing installations keep receiving updates.

CARBON via npm / MCP

The free, MIT-licensed runtime with Jay is also packaged as @testers-ai/carbon-mcp. Requires Node.js 22+; demo and full-workflow helpers also require Python 3.10+.

Use the npm setup guide and verified release artifacts for MCP installation. The source distribution version is not a claim of npm publication.

See the npm setup guide for the 13 MCP workflow prompts, eight tools, host requirements, and privacy boundaries. npm analytics defaults off; npm installation alone does not register native agent hooks or supply model access. The npm release procedure documents source and package checks.

Cursor source candidate: CARBON Core 1.32.23-cursor.5 · Cursor-specific privacy. Bounded native HTTP smoke passed; marketplace review remains pending.

Grok Bot source prerelease: CARBON Core 1.0.2 · Grok-specific privacy. Local protocol tests passed; native Grok testing and marketplace review remain pending.

Your agent's plan. Your local workspace.

Use the model access you already have. In Claude Code, Codex, and other coding agents, CARBON's default testing workflows use the host's configured model access. When the host uses an eligible subscription, CARBON uses that allowance—no separate CARBON model API key is required. If the host uses API credentials or a company LLM proxy, that billing and data policy apply instead. Plan limits and extra-usage charges still apply; CARBON Pro licensing is separate.

Local execution and local reports—not a promise that no data leaves your machine. For local runs, project files, test evidence, and reports are stored in your local workspace. Your coding agent can send selected code, screenshots, prompts, and other context to its configured model provider. Local CARBON is not automatically offline or air-gapped. Cloud runs, external integrations, and optional direct-model checks have separate data flows and may have separate costs. Command-usage analytics vary by edition; review that edition's privacy policy and settings.

To confirm your billing route, check /status in Claude Code or codex login status in Codex. A configured API key can select API billing instead of subscription usage. Standalone MCP clients must supply their own model access and execution tools; installing an MCP server does not include a model subscription.

Free and open source. AI software testing and quality assurance inside Claude.

AI testing inside your coding agent. Built by testers.ai.

CARBON gives your coding agent risk-based testing instructions and a local evidence runtime. The agent inspects your authorized project, runs checks using its available browser, terminal or API tools, and records findings in a live report. CARBON's MCP server does not independently run the investigation or manufacture results.

Visual testing evidence

Four compact report views help you move from a decision to its evidence:

• Release Brief: findings, next actions and outcomes for the selected checks.
• Evidence Lens: page screenshots linked to checks, reproduction and fixes.
• Journey Atlas: recorded paths and step outcomes, without invented connections.
• Live Investigation: the current check, its purpose and recent activity.

Zoom screenshots, keep the full record one click away, and export portable HTML/JSON. Live reports retain their last good snapshot and quietly reconnect after interruption. Unknown and deferred checks remain distinct from passing checks.

Role-based AI testing team

Jay, the AI test manager, now introduces the assessment and appears in reports. Specialist profiles use role-based names and new light/dark icon identities rather than human names and photographs. They remain AI perspectives, not human reviewers. See the AI testing team, visual profile gallery, command guide, and MCP tool reference. Role names describe AI testing perspectives, not independent human review.

Included commands

Twelve distinct commands, with thirteen skill entrypoints including the j alias. Host prefixes differ; Claude normally uses /carbon:command.

All recorded findings, persona journeys, HTML/JSON exports and current-run maps are included. No CARBON account, payment or finding unlock is required. Your coding-agent subscription or API usage is separate. The usual 20-minute/20-check planning default is adjustable, not a coverage guarantee or hard run quota.

Install and start in Claude Code

Requirements: Node.js 22 or later; Python 3.10 or later for the optional demo creator. No npm install is needed for the MCP runtime. Browser automation depends on the tools your coding agent has available. Optional demo tests have their own documented dependencies.

git clone https://github.com/jarbon/carbon-free.git

claude --plugin-dir /absolute/path/to/carbon-free

Replace the path with your checkout. Claude Code normally prefixes plugin skills with the plugin name. Try these three examples:

1. /carbon:carbon — assess the current project. If the folder is empty or the target is unclear, Jay asks what to test: a URL, folder/repository, API, app/feature, or requirements. With a clear target, he runs a broad assessment and reports findings, evidence-qualified confidence, gaps, and next steps.
2. /carbon:carbon-issues ./my-app — investigate bugs, including state transitions and multi-step journeys, in an authorized project.
3. /carbon:carbon-accessibility http://localhost:3000 — test an app you control; report actual evidence and untested criteria separately.

Use /carbon:carbon-map for the latest assessment or /carbon:carbon-settings to adjust defaults. Names and embedded-browser support can vary by host/version; use the host's skill picker. Install one CARBON edition at a time because editions share the carbon namespace. This repository is not a claim of Anthropic approval or listing.

The bundle also contains a Codex manifest. Other MCP hosts may launch node /absolute/path/to/carbon-free/server/index.mjs, then expose the bundled skills through their supported mechanism. A chat host without local process/browser access cannot provide the same runtime behavior. Test the surface you intend to use.

What runs, writes and connects

• The declared MCP entry point is server/index.mjs, using Node standard libraries.
• Demo creation invokes bundled runtime/carbon/scripts/carbon_demo.py via Python. Fixtures are synthetic examples, some intentionally imperfect; never deploy them as production apps.
• Evidence and report snapshots are saved under your project's .carbon/free/. Existing reports are retained. Uninstalling does not erase evidence.
• Live report/settings views bind to 127.0.0.1 and use random access tokens. The agent opens them with its own browser/panel tool where supported. Saved HTML remains usable after the runtime stops. Review exports before sharing.
• Anonymous command analytics is enabled by default and sends fixed command event names to https://cdn.usefathom.com/. It does not send prompts, source, target URLs, screenshots, findings, credentials or a stable user identifier. Network metadata is visible to that service. Set CARBON_ANALYTICS=off before startup or disable analytics in settings. No telemetry is sent merely by importing the module.
• Global analytics preference and delivery diagnostics use .config/carbon/ in your user home. Project evidence has no automatic expiration; you control retention.
• Your coding agent's model provider still processes the context you share with it. Browser/API checks contact the authorized target and potentially its third parties. Local-first does not mean air-gapped.

See the privacy policy for data handling, retention and contact details. There is no private benchmark fetch, reviewer service, remote MCP backend or Pro unlock code in this bundle.

Interpreting results

Only recorded evidence is displayed. Unexecuted tests remain blocked or deferred; suspected issues are distinguished from demonstrated failures. Confidence is scoped engineering judgment, not a calibrated probability that the whole product is correct. AI persona feedback is simulated, not human research. Accessibility results are not a certification or legal opinion. This Free runtime does not generate formal DOCX conformance documents or run continuous automatic repair.

Troubleshooting and support

• Missing tools: check Node with node --version, reload the plugin and inspect the host's MCP connection status. Run claude plugin validate . from the checkout.
• Expired live link: reopen the saved run with carbon_report or open its saved HTML.
• No browser available: run authorized static/API checks and disclose untested UI scope.
• Demo setup failure: check python3 --version and the selected fixture's README.
• Do not post private code, report tokens, screenshots or customer records in public issues.

Product/security support: jason@testers.ai. Reproducible non-sensitive problems: GitHub issues.

Runtime regression checks

From the repository root, run node tests/smoke.mjs .. The checks use temporary synthetic projects and disable analytics. They exercise the MCP interface, demo copying, report lifecycle, evidence exports, settings persistence, authentication, cross-origin rejection and symlink protection. They do not certify accessibility, security, or performance of an application under test.

License and product information

Open source under the MIT Licens