"No-Model-in-the-Loop" MCP retrieval layer cuts coding agent tool calls by 28%
Cryvixx · reddit · 2026-09-09
The author of Silica-core, an open-source MIT retrieval engine exposed over MCP and CLI, shares architecture lessons from enforcing one constraint: the harness owns the loop — tools never summarize or decide, they only return located evidence (file path, section, line window) plus math signals.
- Lexical beats embeddings for agent search: section-aware BM25 avoids the latency, memory footprint, and exact-term blindness of local vector embeddings.
- Give the agent rejection signals: returning coverage (fraction of query IDF mass present) and termsabsent lets the model instantly judge whether a concept exists in the vault.
- Atomic read tools: silicaread serves line slices and section outlines; lightweight outputs cut agent turns by 22% and tool calls by 28% across 144 benchmark runs on 5.5M tokens.
Runs locally via uv with no API keys, telemetry, or background embedding workers.
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