CrateDB: Hello, World!

Author: amotl

README-CRATEDB.md

@@ -0,0 +1,44 @@
+# CrateDB Model Context Protocol Server
+
+## About
+
+This CrateDB MCP Server is based on the PostgreSQL Model Context Protocol (PG-MCP) Server.
+[pg-mcp] uses [asyncpg], so it can also be used with CrateDB.
+
+`server/resources/schema.py` received a few adjustments to compensate for
+missing metadata features of CrateDB, nothing serious.
+
+## Usage
+
+Start CrateDB.
+```shell
+docker run --rm \
+  --name=cratedb --publish=4200:4200 --publish=5432:5432 \
+  --env=CRATE_HEAP_SIZE=2g crate/crate:nightly \
+  -Cdiscovery.type=single-node
+```
+
+Initialize Python environment.
+```shell
+git clone https://github.com/crate-workbench/pg-mcp --branch=cratedb
+cd pg-mcp
+uv venv --python 3.13 --seed .venv
+uv sync --frozen
+```
+
+Run MCP server and test program.
+```shell
+uv run -m server.app
+uv run test.py "postgresql://crate@localhost/doc"
+```
+
+Run example Claude session (untested).
+```shell
+export DATABASE_URL=postgresql://crate@localhost
+export ANTHROPIC_API_KEY=...
+uv run -m client.claude_cli "Give me 5 Austria mountains (querying specific tables, like sys.summits)"
+```
+
+
+[asyncpg]: https://pypi.org/project/asyncpg
+[pg-mcp]: https://github.com/stuzero/pg-mcp

server/resources/schema.py

@@ -14,8 +14,7 @@ async def list_schemas(conn_id: str):
         """List all non-system schemas in the database."""
         query = """
             SELECT 
-                schema_name,
-                obj_description(pg_namespace.oid) as description
+                schema_name
             FROM information_schema.schemata
             JOIN pg_namespace ON pg_namespace.nspname = schema_name
             WHERE 
@@ -30,9 +29,7 @@ async def list_schema_tables(conn_id: str, schema: str):
         """List all tables in a specific schema with their descriptions."""
         query = """
             SELECT 
-                t.table_name,
-                obj_description(format('"%s"."%s"', t.table_schema, t.table_name)::regclass::oid) as description,
-                pg_stat_get_tuples_inserted(format('"%s"."%s"', t.table_schema, t.table_name)::regclass::oid) as total_rows
+                t.table_name
             FROM information_schema.tables t
             WHERE 
                 t.table_schema = $1
@@ -49,8 +46,7 @@ async def get_table_columns(conn_id: str, schema: str, table: str):
                 c.column_name,
                 c.data_type,
                 c.is_nullable,
-                c.column_default,
-                col_description(format('%s.%s', c.table_schema, c.table_name)::regclass::oid, c.ordinal_position) as description
+                c.column_default
             FROM information_schema.columns c
             WHERE
                 c.table_schema = $1 AND
@@ -66,7 +62,6 @@ async def get_table_indexes(conn_id: str, schema: str, table: str):
             SELECT 
                 i.relname as index_name,
                 pg_get_indexdef(i.oid) as index_definition,
-                obj_description(i.oid) as description,
                 am.amname as index_type,
                 ARRAY_AGG(a.attname ORDER BY k.i) as column_names,
                 ix.indisunique as is_unique,
@@ -112,7 +107,6 @@ async def get_table_constraints(conn_id: str, schema: str, table: str):
                     WHEN c.contype = 'x' THEN 'EXCLUSION'
                     ELSE 'OTHER'
                 END as constraint_type_desc,
-                obj_description(c.oid) as description,
                 pg_get_constraintdef(c.oid) as definition,
                 CASE 
                     WHEN c.contype = 'f' THEN 
@@ -149,7 +143,6 @@ async def get_index_details(conn_id: str, schema: str, table: str, index: str):
             SELECT 
                 i.relname as index_name,
                 pg_get_indexdef(i.oid) as index_definition,
-                obj_description(i.oid) as description,
                 am.amname as index_type,
                 ix.indisunique as is_unique,
                 ix.indisprimary as is_primary,
@@ -202,7 +195,6 @@ async def get_constraint_details(conn_id: str, schema: str, table: str, constrai
                     WHEN c.contype = 'x' THEN 'EXCLUSION'
                     ELSE 'OTHER'
                 END as constraint_type_desc,
-                obj_description(c.oid) as description,
                 pg_get_constraintdef(c.oid) as definition,
                 CASE 
                     WHEN c.contype = 'f' THEN 

server/tools/query.py

@@ -78,7 +78,7 @@ async def pg_explain(query: str, conn_id: str, params=None):
             Complete JSON-formatted execution plan
         """
         # Prepend EXPLAIN to the query
-        explain_query = f"EXPLAIN (FORMAT JSON) {query}"
+        explain_query = f"EXPLAIN {query}"
 
         # Execute the explain query
         result = await execute_query(explain_query, conn_id, params)