Memory server

Persistent knowledge-graph memory: entities, relations, and observations, stored as a JSONL file, mirroring the reference @modelcontextprotocol/server-memory server.

• Identity: mcp-memory (crate version)
• Capabilities: tools, resources, resource subscriptions
• Invocation: modelcontextprotocol memory [--memory-file <PATH>] or modelcontextprotocol --memory [--memory-file <PATH>]

Storage

• Format: one JSON object per line — {"type":"entity",...} and {"type":"relation",...} lines in the reference server's format, so a file written by this server is readable by the reference server and vice versa.
• File location precedence: --memory-file flag, then the MEMORY_FILE_PATH environment variable, then memory.jsonl in the current working directory. Relative paths resolve against the working directory at startup.
• Persistence model: every mutation loads the file, applies the change, and rewrites it (a missing file starts as an empty graph). Mutations are serialized by a mutex. A corrupt line fails the operation with an explicit error.
• Written with the process's OS permissions; no encryption (see Security model).

Tools

9 tools. The graph shape is { entities: [{ name, entityType, observations[] }], relations: [{ from, to, relationType }] } (camelCase on the wire).

create_entities

Create multiple entities; names that already exist are ignored. Returns the entities actually added ({ "entities": [...] }).

Parameter	Required	Default	Bounds / notes
entities	yes	—	array of { name, entityType, observations: string[] }

create_relations

Create multiple directed relations; exact duplicates (from, to, relationType all equal) are skipped. Relations should be in active voice. Returns { "relations": [...] }.

Parameter	Required	Default	Bounds / notes
relations	yes	—	array of { from, to, relationType }

add_observations

Add observations to existing entities; fails ("Entity with name ... not found") if any entity does not exist. Duplicates within a single call are all added; only observations already present are filtered. Returns { "results": [{ entityName, addedObservations[] }] }.

Parameter	Required	Default	Bounds / notes
observations	yes	—	array of { entityName, contents: string[] }

delete_entities

Delete entities and cascade-delete their relations. Unknown names are silently ignored. Returns { success: true, message: "Entities deleted successfully" }.

Parameter	Required	Default	Bounds / notes
entityNames	yes	—	array of strings

delete_observations

Delete specific observations from entities; missing entities or observations are silently ignored. Returns a success object.

Parameter	Required	Default	Bounds / notes
deletions	yes	—	array of { entityName, observations: string[] }

delete_relations

Delete specific relations (matched by from, to, relationType); missing relations are silently ignored. Returns a success object.

Parameter	Required	Default	Bounds / notes
relations	yes	—	array of { from, to, relationType }

read_graph

Read the entire knowledge graph (zero parameters).

search_nodes

Case-insensitive substring search across entity names, entity types, and observation contents. Relations with at least one matching endpoint are included, so connections to nodes outside the result set are discoverable. A query with no matches returns an empty graph.

Parameter	Required	Default	Bounds / notes
query	yes	—	string

open_nodes

Open specific entities by name; unknown names are skipped. Relations with at least one endpoint in the requested set are included.

Parameter	Required	Default	Bounds / notes
names	yes	—	array of strings

Resource: knowledge-graph

• URI: memory://knowledge-graph, MIME application/json.
• Contents: the full graph, identical in shape to read_graph, as pretty-printed JSON.
• Listed under the name knowledge-graph in resources/list.

Subscriptions

• Modern (2026-07-28): the server accepts resource_subscriptions for memory://knowledge-graph and holds subscriptions/listen open, sending notifications/resources/updated for the URI after every graph mutation.
• Legacy: the same notifications reach legacy resources/subscribe listeners (both flows share the mutation broadcast channel).

Mutation → notification mapping

Every mutation tool (create_entities, create_relations, add_observations, delete_entities, delete_observations, delete_relations) broadcasts a graph-updated notification after a successful write; read-only tools never notify.

Annotations summary

Tool	RO	ID	DEST
create_entities / create_relations / add_observations	no	no	no
delete_entities / delete_observations / delete_relations	no	yes	yes
read_graph / search_nodes / open_nodes	yes	yes	no

All memory tools have openWorldHint: false.