reflect
Self-correction engine for AI coding agents. An MCP server that implements the Reflexion pattern — turning agent failures into persistent, searchable lessons that prevent the same mistakes across sessions.
cargo install reflect-mcp
The Problem
AI coding agents make mistakes, get corrected, and then make the exact same mistakes in the next session. Context resets wipe everything. There's no memory of what went wrong, what was learned, or which error patterns keep recurring.
How reflect Solves It
reflect closes the loop from the Reflexion paper (Shinn et al., 2023):
generate code → evaluate → critique → store lesson → recall next time → retry smarter
Unlike the original paper which uses LLM self-reflection, reflect takes a hybrid approach:
- Deterministic pattern extraction — regex-based classification of error messages into pattern slugs (e.g.,
rust-unwrap-on-parse,rust-index-oob), no LLM needed - Agent-provided critique — the calling agent writes the reasoning and lesson text, reflect handles structuring, deduplication, storage, and retrieval
- Persistent cross-session memory — SQLite with FTS5 full-text search, so lessons survive context resets
This means reflect is fast, deterministic, and has zero LLM cost for the pattern matching layer, while still benefiting from the agent's reasoning for critique quality.
What Makes reflect Different
Architecture
4-crate Rust workspace:
reflect/
├── crates/
│ ├── reflect-core/ # Types, Storage trait, pattern engine, dedup
│ ├── reflect-eval/ # Test output parsers (cargo_test, pytest, eslint, tsc), command runner
│ ├── reflect-store/ # SQLite + FTS5 (default), optional ctxgraph backend
│ └── reflect-mcp/ # MCP server (rmcp v1.3), 7 tools, config
├── tests/fixtures/ # Captured test outputs for parser testing
├── Cargo.toml # Workspace root
└── Cargo.lock
MCP Tools
Agent Workflow
Before starting a task:
Agent → recall_reflections("implement date parser", tags: ["rust"])
← 3 past lessons about date parsing, including "always handle timezone-naive inputs"
← patterns_to_watch: rust-unwrap-on-parse (seen 7 times)
After a failure:
Agent → evaluate_output(evaluators: ["cargo_test"], working_dir: "/my/project")
← signals: [{evaluator: "cargo_test", passed: false, errors: [{message: "called Result::unwrap() on Err"}]}]
Agent → reflect_on_output(
task: "parse user date input",
draft: "input.parse::<NaiveDate>().unwrap()",
signals: <from above>,
critique: "Used unwrap on user input that can fail",
lesson: "Always use Result handling for parse operations on untrusted input",
outcome: "failure",
tags: ["rust", "error-handling"]
)
← {reflection_id: "...", pattern_id: "rust-unwrap-on-parse", pattern_occurrences: 8, is_duplicate: false}
Installation
Build from source
git clone https://github.com/rohansx/reflect.git
cd reflect
cargo build --release
Binary: target/release/reflect-mcp
Add to Claude Code
Add to ~/.claude.json:
{
"mcpServers": {
"reflect": {
"type": "stdio",
"command": "/path/to/reflect-mcp",
"args": [],
"env": {}
}
}
}
Add to Claude Desktop
Add to claude_desktop_config.json:
{
"mcpServers": {
"reflect": {
"command": "/path/to/reflect-mcp",
"args": []
}
}
}
Configuration
reflect works with zero configuration. Optionally create reflect.toml in your project root or ~/.config/reflect/reflect.toml:
[storage]
path = ".reflect/reflect.db" # default
# backend = "sqlite" # default
# backend = "ctxgraph" # requires --features ctxgraph
[eval.cargo_test]
command = "cargo test"
timeout_secs = 60
[eval.pytest]
command = "pytest --tb=short -q"
timeout_secs = 120
[eval.eslint]
command = "npx eslint . --format stylish"
timeout_secs = 60
[eval.tsc]
command = "npx tsc --noEmit"
timeout_secs = 60
# Custom evaluator — any command that returns exit 0 for pass
[eval.mypy]
command = "mypy src/"
timeout_secs = 90
[recall]
default_limit = 5
dedup_threshold = 0.75 # normalized Levenshtein similarity
# Custom pattern rules
[[patterns]]
evaluator = "cargo_test"
regex = "connection refused"
id = "db-connection-refused"
category = "infrastructure"
Environment variables:
REFLECT_CONFIG— path to config file (overrides search)REFLECT_DB— path to SQLite database (overrides config)
Key Design Decisions
Why regex pattern matching instead of LLM classification? Deterministic, zero-cost, reproducible. Error messages follow predictable formats. Custom rules in TOML for project-specific patterns.
Why SQLite + FTS5 as default instead of vector embeddings? No external dependencies, instant startup, full-text search is good enough for task-description similarity. For better recall, enable the optional ctxgraph backend which adds 384-dim embedding search with RRF ranking.
Why the agent provides critique text? The agent has full context (code, intent, constraints). reflect adds structure (timestamps, confidence, patterns, dedup) — each does what it's best at.
Why UUIDv7? Time-ordered, sortable, globally unique. No sequence coordination needed.
Why Laplace smoothing for confidence?
0.5 + (validations - contradictions) / (validations + contradictions + 2) — starts neutral (0.5), converges with evidence, never reaches 0 or 1 with finite data.
ctxgraph Backend (Optional)
For embedding-based semantic search and cross-project reflection retrieval, build with the ctxgraph feature:
cargo build --release --features ctxgraph
Then set the backend in reflect.toml:
[storage]
backend = "ctxgraph"
path = ".reflect/reflect.db"
This uses ctxgraph's fused search (FTS5 + 384-dim AllMiniLML6V2 embeddings with RRF ranking) for more accurate recall. Reflections are stored as ctxgraph Episodes with graph-structured pattern tracking via Entities and Edges.
Roadmap
- Phase 1 (done): Core loop — cargo_test parser, SQLite+FTS5, 7 MCP tools, pattern engine, dedup
- Phase 2 (done): Multi-language — pytest, eslint, tsc parsers, configurable dedup, pattern rules for Python/JS/TS
- Phase 3 (done): Semantic search via ctxgraph as optional storage backend (
--features ctxgraph) - Phase 4: Distribution — crates.io, Homebrew, documentation site
References
- Shinn, N., Cassano, F., Gopinath, A., Narasimhan, K., & Yao, S. (2023). Reflexion: Language Agents with Verbal Reinforcement Learning. NeurIPS 2023.
- Model Context Protocol — the transport layer
- rmcp — Rust MCP SDK
License
MIT