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How to give Claude Code a persistent, queryable memory with Lemmalog

Register the Lemmalog MCP server so Claude Code can assert facts, query them and trace each answer back to its source.

Who it is forA developer running Claude Code on a multi-session project who keeps losing track of decisions, people and facts established in earlier sessions.

The problemChat context is lost between sessions, and a vector store retrieves text without showing how a conclusion was derived.

The outcomeClaude Code stores facts with lemmalog_observe, derives conclusions with rules, and uses lemmalog_why to show the proof tree back to the episodes that support each conclusion.

What you need first

  • Rust toolchain with cargo, and a clone of the lemmalog repo
  • Claude Code (or Kimi CLI) installed if you want MCP tools
  • A writable path for the memory snapshot, for example /tmp/lemmalog.snapshot or the default ~/.lemmalog/memory.snap

Steps

  1. Run cargo build --release in the repo to produce the lemmalog-cli binary used by later steps. (inferred, check the README)
  2. Run cargo build --release --features mcp.
  3. Run claude mcp add lemmalog -- $(pwd)/target/release/lemmalog-mcp.
  4. Optionally register with persistence: claude mcp add lemmalog --env LEMMALOG_MCP_PATH=/tmp/lemmalog.snapshot -- $(pwd)/target/release/lemmalog-mcp. (inferred, check the README)
  5. In Claude Code, call lemmalog_observe with facts such as Alice --works_at--> Acme and then lemmalog_query with a goal such as current("Alice", R, O), quoting entity names. (inferred, check the README)

Prompt for your agent

Using the lemmalog MCP server in <project>, assert the facts stated in this session with lemmalog_observe, then run lemmalog_query for each decision made. Expected output: the query results for each decision, plus a lemmalog_why proof tree for one derived fact. Verify that every observed line returned no dropped-line warning.

Caveat. The README warns that the MCP server and headless CLI hold separate in-process copies, so do not write from both at the same time against one snapshot.

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