Serena
Open-source toolkit from Oraios, under the MIT licence, exposed as an MCP server, that gives a coding agent the moves of an IDE: find a symbol, its references and its type hierarchy, then edit or refactor at symbol level instead of by line. By default it relies on language servers, so on the actual structure of the code, with over 40 languages supported. It works with Claude Code, Claude Desktop, Codex and MCP-capable IDEs; a paid JetBrains plugin is an alternative to the language server backend.
Strengths
- Navigation on the actual code structure through language servers, not on text
- Symbol-level edits: fewer fragile line replacements
- Over 40 languages and several clients: Claude Code, Codex, Claude Desktop, MCP-capable IDEs
- MIT licence, free language server backend by default
Limitations
- Pointless on a small repo where grep and context are enough
- Needs uv and Python 3.13, then a launch configuration specific to each client
- The richer JetBrains backend is paid
Best for
- A repo too large for the agent to reread in full before each change
- Multi-file refactors where one forgotten caller breaks production