AndyL
ElixirLS MCP Server
With this week’s release, ElixirLS bundles an experimental MCP Server. (see CHANGELOG)
Highlights
- Added Call hierarchy provider implementing LSP textDocument/prepareCallHierarchy, callHierarchy/incomingCalls and callHierarchy/outgoingCalls
- ElixirLS now bundles a number of experimental LLM oriented tools exposed as custom commands and a builtin MCP server. The tools focus on model friendly text interface instead of typical IDE oriented LSP API methods. Refer to README.md on how to connect to the MCP server. The tools include:
find_definition- Find and retrieve the source code of symbols.get_environment- Retrieve environment at location with aliases, imports, requires and more.get_docs- Aggregate and return comprehensive documentationget_type_info- Extract typespecs and contracts.find_implementations- Find all implementations of behaviours and protocols.get_module_dependencies- Analyze module dependency relationships- Unofficial support for elixir 1.19
Thanks to @lukaszsamson for this new feature. I’m curious to hear user reports!
- configuring to use with Claude Code, OpenCode, etc.
- compare/contrast with Tidewave
- integration with UsageRules or other coding aids
- pro-tips, benefits, drawbacks, opportunities, concerns, etc.
Most Liked
cvkmohan
Thanks. My experience is something similar. When I am using claude cli - firstly, it does not use the tools all that much - and - repeated nudging does not help much. In fact, if we are using plain claude cli - there will be zero difference between having any MCP or completely raw setup.
However, I have realized things change dramatically once we change the agent. Two examples that I can readily show:
- Zed Editor. When I am using the Zed editor - and - same claude sonnet 4 model - MCP calling, overall output quality dramatically improves. Everything else same. So, what Zed is giving as input to the LLM model is quite different from what claude cli gives to LLM. And that is making a lot of difference.
- OpenCode. When I am using the opencode cli - and - same claude sonnet 4 model - suppose I am using it for fixing failed tests. The way OpenCode approaches the problem is hugely different from how the same is done via claude cli. With opencode it will fix the code in the most optimal way in the fastest time with lower tokens. Nothing certain about claude cli.
Again both these tools (Zed, OpenCode) are using LSP or some semantic tool as part of the prompt. And it is showing its impact. How can it be enhanced is the question. That is where everyone is still in exploratory mode.
I can say with reasonable conviction that these graph databases, vector embeddings etc. are not that useful - atleast for code generation.
arcanemachine
Shouldn’t this be an opt-in feature?
Personally, I just started playing with MCP very recently. I’m working with Ollama and Open Web UI. I tried getting Tidewave to work… I got to respond to my requests, but I couldn’t actually get anything useful out of it. It wouldn’t even eval my “hello world” function. 
arcanemachine
The newest patch release makes MCP opt-in, not opt-out:
garrison
Interesting. Looks like it’s enabled by default so for those of us who want to turn it off elixirLS.mcpEnabled = false will take care of it.
I’m curious how many here are now using these agentic tools. Do we have a rough percentage?
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