| **Sigmoid score compression.** Raw scores are mapped through a sigmoid function, approaching 1.0 asymptotically. High-relevance results remain distinguishable instead of being crushed into the same value. |
| 
| **Ebbinghaus forgetting curve.** Exponential decay with kind-differentiated rates — episodic memories fade fastest, procedural slowest. Floor at 0.01 means memories never fully vanish; they remain retrievable under precise queries. |
| 
| **Kind × layer weight bias.** Additive biases adjust memory weight by type and layer. Procedural+core memories rank highest, episodic+buffer lowest — but the spread stays bounded so no single combination dominates. |
| 
| **Reinforcement signals.** Repetition and access bonuses follow logarithmic saturation. Early interactions matter most; later ones contribute diminishing returns, discriminating between "used occasionally" and "used daily". |
| 
| **Use it or lose it.** Left: a memory that's never recalled decays into the buffer layer. Right: periodic recall triggers activation boosts that keep the memory in the working layer. Dashed line shows the unrecalled trajectory for comparison. |
### Semantic Dedup & Merge
Two memories saying the same thing in different words? Detected and merged automatically:
```
"use PostgreSQL for auth" + "auth service runs on Postgres"
→ Merged into one, preserving context from both
```
### Self-Organizing Topic Tree
Vector clustering groups related memories together, LLM names the clusters. No manual tagging required:
```
Memory Architecture
├── Three-layer lifecycle [4]
├── Embedding pipeline [3]
└── Consolidation logic [5]
Deploy & Ops
├── CI/CD procedures [3]
└── Production incidents [2]
User Preferences [6]
```
The problem this solves: vector search requires asking the right question. Topic trees let agents **browse by subject** — scan the directory, drill into the right branch.
### Triggers
Tag a memory with `trigger:deploy`, and the agent can recall all deployment lessons before executing:
```bash
curl -X POST http://localhost:3917/memories \
-d '{"content": "LESSON: always backup DB before migration", "tags": ["trigger:deploy", "lesson"]}'
# Pre-deployment check
curl http://localhost:3917/triggers/deploy
```
## Session Recovery
Agent wakes up, calls `GET /resume`, gets full context back. No file scanning needed:
```
=== Core (24) ===
deploy: test → build → stop → start (procedural)
LESSON: never force-push to main
...
=== Recent ===
switched auth to OAuth2
published API docs
=== Topics (Core: 24, Working: 57, Buffer: 7) ===
kb1: "Deploy Procedures" [5]
kb2: "Auth Architecture" [3]
kb3: "Memory Design" [8]
...
Triggers: deploy, git-push, database-migration
```
| Section | Content | Purpose |
|---------|---------|---------|
| **Core** | Full text of permanent rules and identity | The unforgettable stuff |
| **Recent** | Recently changed memories | Short-term continuity |
| **Topics** | Topic index (table of contents) | Drill in on demand, no full load |
| **Triggers** | Pre-action tags | Auto-recall lessons before risky ops |
Agent reads the directory, finds relevant topics, calls `POST /topic` to expand on demand.
## Search & Retrieval
Semantic embeddings + BM25 keyword search with CJK tokenization ([jieba](https://github.com/messense/jieba-rs)). IDF-weighted scoring — rare terms get boosted, common terms auto-downweighted. No stopword lists to maintain.
```bash
# Semantic search
curl -X POST http://localhost:3917/recall \
-d '{"query": "how do we handle auth", "budget_tokens": 2000}'
# Note: min_score defaults to 0.30. Use "min_score": 0.0 to get all results.
# Topic drill-down
curl -X POST http://localhost:3917/topic \
-d '{"ids": ["kb3"]}'
```
## Background Maintenance
Fully automatic, activity-driven — no writes means the cycle is skipped:
**Consolidation (every 30 minutes)**
1. **Decay** — reduce importance of unaccessed memories
2. **Dedup** — merge near-identical memories (cosine > 0.78)
3. **Triage** — LLM categorizes new Buffer memories
4. **Gate** — LLM batch-evaluates promotion candidates
5. **Reconcile** — resolve ambiguous similar pairs (results cached)
6. **Topic tree rebuild** — re-cluster and name
**Topic Distillation** — when a topic grows too large (10+ memories), overlapping content is condensed into fewer, richer entries.
## Namespace Isolation
Single instance, multiple projects. Use `X-Namespace` to isolate:
```bash
curl -X POST http://localhost:3917/memories \
-H "X-Namespace: my-project" \
-d '{"content": "API uses OAuth2 bearer tokens"}'
```
## Install
```bash
# macOS / Linux
curl -fsSL https://raw.githubusercontent.com/kael-bit/engram-rs/main/install.sh | bash
# Windows (PowerShell)
irm https://raw.githubusercontent.com/kael-bit/engram-rs/main/install.ps1 | iex
```
### Docker
```bash
docker run -d --name engram-rs \
-p 3917:3917 \
-v engram-data:/data \
-e ENGRAM_LLM_URL=https://api.openai.com/v1 \
-e ENGRAM_LLM_KEY=sk-... \
ghcr.io/kael-bit/engram-rs:latest
```
### LLM Configuration
engram-rs works without an LLM — keyword search and rule-based lifecycle still function. Adding an LLM unlocks intelligent features (triage, gate, merge, topic naming):
```bash
export ENGRAM_LLM_URL=https://api.openai.com/v1
export ENGRAM_LLM_KEY=sk-...
# Any OpenAI-compatible API (Ollama, LM Studio, etc.)
export ENGRAM_LLM_URL=http://localhost:11434/v1
# Anthropic native
export ENGRAM_LLM_PROVIDER=anthropic
export ENGRAM_LLM_KEY=sk-ant-...
```
Two-tier model config — strong model for judgment, lightweight for text processing:
```bash
ENGRAM_GATE_MODEL=gpt-4o # quality decisions
ENGRAM_LLM_MODEL=gpt-4o-mini # text processing
```
### For AI Agents
Add to your agent's system prompt:
```
Set up engram-rs (persistent memory) by following the guide at:
https://raw.githubusercontent.com/kael-bit/engram-rs/main/docs/SETUP.md
```
## Integration
Works with Claude Code, Cursor, Windsurf, OpenClaw, and any MCP-compatible tool.
17 MCP tools ([MCP docs](docs/MCP.md)) | Full HTTP API ([Setup guide](docs/SETUP.md))
```bash
# MCP (Claude Code)
npx engram-rs-mcp
# MCP (Cursor / Windsurf / generic)
{"mcpServers": {"engram": {"command": "npx", "args": ["-y", "engram-rs-mcp"]}}}
```
### Web Dashboard
Built-in web UI at `http://localhost:3917/ui` for browsing memories, viewing the topic tree, and monitoring LLM usage.
## Specs
| | |
|---|---|
| Binary | ~10 MB |
| Memory | ~100 MB RSS in production |
| Storage | SQLite, no external database |
| Language | Rust |
| Platforms | Linux, macOS, Windows (x86_64 + aarch64) |
| License | MIT |
## License
MIT