Skylos

What it does

Skylos is a static analysis tool, and its Python package ships an MCP server (the skylos_mcp.server module) that gives an MCP client the same engine the skylos CLI uses. The assistant passes a folder or file path and gets structured findings back: unused functions, imports and classes with confidence scores, taint-tracked injection and SSRF issues, hard-coded keys, complexity and architecture problems, and supply-chain risks such as imported packages that do not exist on the registry. Python has the deepest coverage; TypeScript/JavaScript and Java get dead-code, security and quality checks, while PHP, Dart, Rust, C#, Kotlin and Shell get narrower coverage. Since 4.50 the PyPI wheels for Linux, macOS and Windows on x86_64 and arm64 bundle the skylos-go engine that Go checks need; on other platforms it has to be built separately.

Beyond scanning, some tools are meant for coding agents: checking a diff or an edited line range for hallucinated references and removed controls, scoring an AI agent's guardrails against OWASP lists, attributing changes to bots or people from git history, and learning from triage decisions. Two tools can change code. generate_fix builds a patch that deletes or comments out dead code and writes it only with apply=true. remediate plans fixes by default; with dry_run=false it asks an LLM for fixes and edits files in place. At v5.0.0 it does not run your tests and rejects test_cmd over MCP, although the docs page still says it validates fixes with tests and reverts broken ones.

The server file at v5.0.0 (skylos_mcp/server.py) registers sixteen tools. The README and docs also describe a change_map tool, but that file does not register it. Every result is saved to ~/.skylos/mcp_results/ (or SKYLOS_MCP_RESULTS_DIR) and can be read back through skylos://results resources.

What it needs

Install skylos (pip install skylos) in the Python interpreter the client starts; the docs' config points at a venv's python when it lives in one. Create SKYLOS_API_KEY in the skylos.dev dashboard settings. remediate with dry_run=false and verify_dead_code need the LLM extra (pip install "skylos[llm]", which brings litellm) plus credentials for the model provider in the server's environment (the docs name OPENAI_API_KEY and ANTHROPIC_API_KEY, or SKYLOS_LLM_BASE_URL for a local model). Go checks outside the bundled wheel platforms need the skylos-go engine built separately; skylos doctor prints the build command.

Limits

• Rate limit Without SKYLOS_API_KEY only analyze works, 5 calls per rolling 24 hours; the other fifteen tools return an authentication error (skylos_mcp/auth.py).
• Rate limit With a key, calls are capped per hour by plan: 50 Free, 500 Pro, 5,000 Enterprise (auth.py).
• Cost remediate costs 10 credits per call per the README. At v5.0.0 Enterprise is charged too, despite the docs page's 'unlimited credits' line (auth.py).
• Cost With a key, analyze and the security, quality, architecture, health, secrets and provenance tools also go through a credit deduction on skylos.dev, and Skylos Cloud sets their cost.
• Limit With a key set, credit-tracked tools are blocked when skylos.dev cannot confirm the deduction, for example when you are offline.
• Limit If the key check fails at start, or the 15-minute recheck fails, the server drops to keyless mode (analyze only).
• Not covered remediate does not run tests over MCP and rejects test_cmd; the docs page's 'validate with tests, revert if broken' does not hold at v5.0.0.
• Not covered change_map is in the README and docs but is not registered by server.py at v5.0.0.
• Limit validate_code_change accepts a policy path but does not apply it to the result at v5.0.0.
• Limit Relative paths resolve against the server's working directory, not the client's project.

Without SKYLOS_API_KEY only analyze works, capped at 5 calls a day (skylos_mcp/auth.py); the other fifteen tools return an authentication error. With a key, calls are capped per hour by plan: 50 free, 500 Pro, 5,000 Enterprise. remediate costs 10 credits per call except on Enterprise plans. The key is checked against skylos.dev when the server starts; if that check fails, the server falls back to the keyless mode. The plain pip install does not bring litellm, so the LLM tools fail until the skylos[llm] extra is added; the MCP docs page does not mention this. Relative paths resolve against the server's working directory.

Who it suits

Developers who want an assistant to scan a local codebase for dead code, injection flaws or leaked keys, and agents that should check their own edits before a person sees them. Analysis runs on your machine, so it fits private code, but most tools need a skylos.dev account key. With a key, the server must reach skylos.dev for credit checks, so it does not suit offline or air-gapped use. Keyless use is limited to one tool five times a day. If you cannot create an account, the skylos CLI (skylos verify, skylos defend, skylos . -a) runs the same checks locally with no key.