Fossil MCP

Fossil MCP is an open-source static analysis toolkit from yfedoseev that targets the artifacts AI-assisted and vibe-coded projects accumulate: dead code, duplicated logic, scaffolding markers, and temp files. It runs both as a command-line tool and as an MCP server that AI coding agents can connect to. The latest release listed on GitHub is v0.1.8.

What It Is

Fossil is a code quality tool built in Rust that parses source files into tree-sitter ASTs, builds a cross-file code graph, and reports findings as a text dashboard, JSON, or SARIF. The project states support for 15-16 languages (the sources differ on the count), including Python, JavaScript, TypeScript, Rust, Go, Java, C#, C/C++, Ruby, PHP, Swift, Kotlin, Scala, and Bash. It is designed to work without configuration, with an optional fossil.toml file for thresholds and entry points.

What It Detects

• Dead code: unreachable functions, unused exports, and orphaned methods, with configurable confidence levels.
• Code clones: Type 1 (exact), Type 2 (renamed), and Type 3 (structural) duplicates.
• Scaffolding: Phase N / Step N comments, placeholder bodies, optional TODO/FIXME markers, and debug prints.
• Temp files: temp_, backup_, old_, and phase_ files and directories.
• Code graph queries: call paths between functions, blast radius, call graph, data flow, and control flow inspection.

It auto-detects framework presets such as React, Next.js, Django, Spring, and Axum so lifecycle methods and route handlers are not flagged as dead.

MCP Server and Agent Workflow

Running fossil-mcp with no arguments starts it as an MCP server when used by an agent. Exposed tools include scan_all, analyze_dead_code, detect_clones, fossil_refresh, fossil_inspect, fossil_trace, fossil_explain_finding, and fossil_detect_scaffolding. Setup instructions are provided for Claude Code, Codex, Cursor, VS Code, Windsurf, Claude Desktop, and others.

CLI and CI Usage

Commands include scan, dead-code, clones, scaffolding, and an interactive REPL for exploring findings. A check command fails builds when configured thresholds are exceeded, supports diff-aware analysis against a base branch, and can emit SARIF for GitHub code scanning.