Memory MCP Server

Memory MCP

A SQLite-backed MCP server for persistent memory storage, full-text retrieval, and relationship graph traversal.

Overview

Memory MCP provides a local, persistent memory layer for MCP-enabled assistants. It stores SHA-256-addressed memory items in SQLite with FTS5-powered full-text search, a directed relationship graph, BFS recall traversal, and token-budget-aware context retrieval — all accessible over stdio transport with no external dependencies.

Key Features

• 13 MCP tools for CRUD, batch operations, FTS5 search, BFS graph recall, token-budget context retrieval, relationships, and stats.
• Full-text search over content and tags via SQLite FTS5 with importance and type filters.
• Graph recall with BFS traversal, bounded frontier, and MCP progress notifications per hop.
• Token-budget retrieval (retrieve_context) selects memories that fit a caller-specified token budget — no manual pagination needed.
• Strict Zod input validation with typed output envelopes and SHA-256 hash addressing.
• Resource support with internal://instructions (Markdown guide) and memory://memories/{hash} URI template with hash auto-completion.
• stdio transport with clean shutdown handling (SIGINT, SIGTERM) and no HTTP endpoints. |

Requirements

• Node.js >=24.
• SQLite with FTS5 support (verified at startup).
• Any MCP client that supports stdio command servers.

Quick Start

Use the npm package directly with npx — no installation required:

{
  "mcpServers": {
    "memory-mcp": {
      "command": "npx",
      "args": ["-y", "@j0hanz/memory-mcp@latest"]
    }
  }
}

[!TIP] The server uses stdio transport only; no HTTP endpoint is exposed. Stdout must not be polluted by custom logging.

Or run with Docker:

docker run --rm -i ghcr.io/j0hanz/memory-mcp:latest

Client Configuration

Workspace file .vscode/mcp.json:

{
  "servers": {
    "memory-mcp": {
      "command": "npx",
      "args": ["-y", "@j0hanz/memory-mcp@latest"]
    }
  }
}

CLI:

code --add-mcp '{"name":"memory-mcp","command":"npx","args":["-y","@j0hanz/memory-mcp@latest"]}'

CLI:

code-insiders --add-mcp '{"name":"memory-mcp","command":"npx","args":["-y","@j0hanz/memory-mcp@latest"]}'

~/.cursor/mcp.json:

{
  "mcpServers": {
    "memory-mcp": {
      "command": "npx",
      "args": ["-y", "@j0hanz/memory-mcp@latest"]
    }
  }
}

claude_desktop_config.json:

{
  "mcpServers": {
    "memory-mcp": {
      "command": "npx",
      "args": ["-y", "@j0hanz/memory-mcp@latest"]
    }
  }
}

CLI:

claude mcp add memory-mcp -- npx -y @j0hanz/memory-mcp@latest

MCP config:

{
  "mcpServers": {
    "memory-mcp": {
      "command": "npx",
      "args": ["-y", "@j0hanz/memory-mcp@latest"]
    }
  }
}

# Pull and run (stdio mode)
docker run --rm -i \
  -e MEMORY_DB_PATH=/data/memory.db \
  -v memory-data:/data \
  ghcr.io/j0hanz/memory-mcp:latest

MCP client config:

{
  "mcpServers": {
    "memory-mcp": {
      "command": "docker",
      "args": [
        "run",
        "--rm",
        "-i",
        "-e",
        "MEMORY_DB_PATH=/data/memory.db",
        "-v",
        "memory-data:/data",
        "ghcr.io/j0hanz/memory-mcp:latest"
      ]
    }
  }
}

Documentation Maintenance

• Owner: maintainers updating MCP behavior in src/ must update README.md and affected mcp/ mirror pages in the same PR.
• Link/version policy: use pinned https://modelcontextprotocol.io/specification/2025-11-25/... links for protocol references; avoid latest and mixed legacy targets.
• Drift-check checklist:
  • Re-verify capability declarations in src/server.ts.
  • Reconcile tool/resource/prompt docs with src/tools/index.ts, src/resources/index.ts, and src/prompts/index.ts.
  • Confirm limitations/gotchas in src/instructions.md match runtime behavior.
• Validation commands: npm run type-check, npm run test:fast, npm run build.

MCP Surface

Tools Summary

Tool	Category	Notes
store_memory	Write	Idempotent by content+sorted tags hash
store_memories	Write	Batch (1–50), transaction-wrapped
get_memory	Read	Hash lookup
update_memory	Write	Returns old_hash + new_hash
delete_memory	Write	Cascades relationship deletion
delete_memories	Write	Batch (1–50), transaction-wrapped
search_memories	Read	FTS5 + importance/type filters + cursor
create_relationship	Write	Idempotent directed edge creation
delete_relationship	Write	Deletes exact directed edge
get_relationships	Read	Direction filter + linked memory fields
recall	Read	FTS5 seed + BFS traversal (depth 0–3)
retrieve_context	Read	Token-budget-aware context retrieval
memory_stats	Read	Store aggregates and type breakdown

---

store_memory

Store a new memory with content, tags, and optional type/importance. Idempotent — storing the same content+tags returns the existing hash with created: false.

Name	Type	Required	Default	Description
content	string	Yes	—	Memory content (1–100000 chars)
tags	string[]	Yes	—	1–100 tags, each max 50 chars, no whitespace
memory_type	enum	No	general	general, fact, plan, decision, reflection, lesson, error, gradient
importance	integer	No	0	Priority 0–10

Returns: { hash, created }

---

store_memories

Store multiple memories in one transaction (max 50 items).

Name	Type	Required	Description
items	Array<StoreMemoryItem>	Yes	1–50 items, each with content, tags, optional memory_type, optional importance

Returns: { items, succeeded, failed }

---

get_memory

Retrieve one memory by its SHA-256 hash.

Name	Type	Required	Description
hash	string	Yes	64-char lowercase SHA-256 hex

Returns: Memory or { ok: false, error } on E_NOT_FOUND.

---

update_memory

Update content and optionally tags for an existing memory. Returns both hashes.

Name	Type	Required	Default	Description
hash	string	Yes	—	Existing memory hash
content	string	Yes	—	Replacement content
tags	string[]	No	Existing tags	Replacement tags

Returns: { old_hash, new_hash }

---

delete_memory

Delete one memory by hash. Cascades to related relationship rows.

Name	Type	Required	Description
hash	string	Yes	Memory hash

Returns: { hash, deleted }

---

delete_memories

Delete multiple memories by hash in one transaction.

Name	Type	Required	Description
hashes	string[]	Yes	1–50 memory hashes

Returns: { items, succeeded, failed }

---

search_memories

Full-text search over memory content and tags using FTS5. Supports importance and type filters with cursor pagination.

Name	Type	Required	Default	Description
query	string	Yes	—	Search text (1–1000 chars)
limit	integer	No	20	Results per page (1–100)
cursor	string	No	—	Pagination cursor from previous response
min_importance	integer	No	—	Only return memories with importance >= this value (0–10)
max_importance	integer	No	—	Only return memories with importance <= this value (0–10)
memory_type	enum	No	—	Filter by memory type

Returns: { memories, total_returned, nextCursor? }

---

create_relationship

Create a directed relationship edge between two memories. Idempotent.

Suggested relation_type values: related_to, causes, depends_on, parent_of, child_of, supersedes, contradicts, supports, references.

Name	Type	Required	Description
from_hash	string	Yes	Source memory hash
to_hash	string	Yes	Target memory hash
relation_type	string	Yes	Edge label (1–50 chars, no whitespace, free-form)

Returns: { created }

---

delete_relationship

Delete one directed relationship edge.

Name	Type	Required	Description
from_hash	string	Yes	Source hash
to_hash	string	Yes	Target hash
relation_type	string	Yes	Relationship type

Returns: { deleted } or { ok: false, error } on E_NOT_FOUND.

---

get_relationships

Retrieve relationships for a memory, with optional direction filter.

Name	Type	Required	Default	Description
hash	string	Yes	—	Memory hash
direction	enum	No	both	outgoing, incoming, or both

Returns: { relationships, count }

Each relationship includes from_hash, to_hash, relation_type, created_at, linked_hash, linked_content, and linked_tags.

---

recall

Search memories by full-text query, then traverse the relationship graph up to depth hops via BFS. Emits MCP progress notifications per hop.

Name	Type	Required	Default	Description
query	string	Yes	—	Seed search query (1–1000 chars)
depth	integer	No	1	BFS hops (0–3)
limit	integer	No	10	Seed memory count (1–50)
cursor	string	No	—	Pagination cursor from previous response
min_importance	integer	No	—	Seed filter: only memories with importance >= value (0–10)
max_importance	integer	No	—	Seed filter: only memories with importance <= value (0–10)
memory_type	enum	No	—	Seed filter: only memories of this type

Returns: { memories, graph, depth_reached, aborted?, nextCursor? }

Each item in graph uses the shape:

{ "from_hash": "...", "to_hash": "...", "relation_type": "..." }

[!NOTE] aborted: true indicates the traversal hit a safety limit (RECALL_MAX_FRONTIER_SIZE, RECALL_MAX_EDGE_ROWS, or RECALL_MAX_VISITED_NODES). Partial results are still returned.

---

retrieve_context

Search memories and return relevance-ranked results that fit within a caller-specified token budget. Eliminates manual pagination and token counting for context window management.

Name	Type	Required	Default	Description
query	string	Yes	—	Search query (1–1000 chars)
token_budget	integer	No	4000	Maximum estimated tokens to return (100–200000)
strategy	enum	No	relevance	Sort order: relevance (FTS rank), importance (highest first), recency (newest first)

Returns: { memories, estimated_tokens, truncated }

[!TIP] Token estimation is approximate (content length ÷ 4). truncated: true means the budget was reached before all candidates were included.

---

memory_stats

Return aggregate memory and relationship stats. Takes no input.

Returns:

{
  "memories": {
    "total": 0,
    "oldest": null,
    "newest": null,
    "avg_importance": null
  },
  "relationships": { "total": 0 },
  "by_type": {}
}

---

Resources

URI	MIME	Description
internal://instructions	text/markdown	Markdown usage guide for all tools and workflows
memory://memories/{hash}	application/json	Returns one memory as JSON; hash completion supported

Prompts

Name	Arguments	Purpose
get-help	none	Returns full usage instructions for all tools

Configuration

Environment Variables

Variable	Description	Default	Required
MEMORY_DB_PATH	SQLite database file path	memory_db/memory.db	No
RECALL_MAX_FRONTIER_SIZE	Max BFS frontier nodes per hop (100–50000)	1000	No
RECALL_MAX_EDGE_ROWS	Max relationship rows fetched per traversal (100–50000)	5000	No
RECALL_MAX_VISITED_NODES	Max visited nodes across entire traversal (100–50000)	5000	No

[!IMPORTANT] If MEMORY_DB_PATH is relative (including the default memory_db/memory.db), it resolves from the process working directory.

[!TIP] Add memory_db/ to your .gitignore to keep the database out of version control — it contains local session data and should not be shared or committed.

Limits and Constraints

Item	Value
Content length	1–100000 chars
Tag count	1–100 per memory
Tag length	1–50 chars, no whitespace
Hash format	64-char lowercase hex SHA-256
Search query length	1–1000 chars
search_memories.limit	1–100 (default 20)
recall.depth	0–3 (default 1)
recall.limit	1–50 (default 10)
retrieve_context.token_budget	100–200000 (default 4000)
Batch size	1–50 items (store_memories, delete_memories)
Recall frontier guard	RECALL_MAX_FRONTIER_SIZE (default 1000 per hop)
SQLite busy timeout	5000 ms

[!NOTE] Cursor values are opaque base64url-encoded tokens. Treat them as opaque and do not parse them.

Security

• Transport is stdio-only (StdioServerTransport) — no HTTP endpoints.
• Fatal process errors are written to stderr; stdout must remain clean for the MCP protocol.
• All inputs are validated with strict Zod schemas and bounded field constraints before any database access.
• Hashes are validated against a lowercase 64-char SHA-256 hex regex.
• Search input is tokenized to alphanumeric terms before FTS MATCH execution (non-alphanumeric characters act as delimiters, preventing FTS injection).
• SQLite foreign keys are enabled; relationship rows cascade-delete when a memory is removed.

Development

Install dependencies:

npm install

Core scripts:

Script	Command	Purpose
build	npm run build	Clean, compile, validate instructions, copy assets, chmod executable
dev	npm run dev	TypeScript watch mode
dev:run	npm run dev:run	Run built server with .env and file watch
start	npm run start	Start built server
test	npm run test	Full build + tests via task runner
test:fast	npm run test:fast	Run TS tests directly with Node test runner
lint	npm run lint	ESLint checks
lint:fix	npm run lint:fix	ESLint auto-fix
type-check	npm run type-check	Strict TypeScript checks
format	npm run format	Prettier format
inspector	npm run inspector	Build and open MCP Inspector against stdio server

Inspect with MCP Inspector:

npx @modelcontextprotocol/inspector node dist/index.js

Build & Release

GitHub Actions release workflow (.github/workflows/release.yml) handles versioning, validation, and publishing via a single workflow_dispatch trigger:

workflow_dispatch (patch / minor / major / custom)
    │
    ▼
  release — bump package.json + server.json → lint → type-check → test → build → tag → GitHub Release
    │
    ├──► publish-npm ──► publish-mcp   (npm Trusted Publishing OIDC → MCP Registry)
    │
    └──► publish-docker                (GHCR, linux/amd64 + linux/arm64)

Trigger a release:

gh workflow run release.yml -f bump=patch

Or use the GitHub UI: Actions → Release → Run workflow.

[!NOTE] npm publishing uses OIDC Trusted Publishing — no NPM_TOKEN secret required. MCP Registry uses GitHub OIDC. Docker uses the built-in GITHUB_TOKEN.

Troubleshooting

Symptom	Cause	Fix
Startup fails with FTS5 error	Node.js build without FTS5	Use Node.js 24+ with SQLite FTS5 support
E_NOT_FOUND on get_memory	Hash doesn't exist	Verify via search_memories first
E_INVALID_CURSOR	Stale or malformed cursor	Retry the request without the cursor parameter
MCP client can't connect	Custom stdout logging added	Ensure nothing writes to stdout in the server process
aborted: true in recall	Traversal hit a safety limit	Reduce depth, or tune RECALL_MAX_* env vars
Database locked errors	High concurrent write load	SQLite busy timeout is 5000 ms; reduce concurrent writes

License

MIT