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MongoDB MCP server has reasonable parameter schema coverage and mostly clear descriptions, but suffers from several medium-severity issues: (1) Generic parameter names and descriptions that don't follow verb_noun conventions; (2) Missing output schema documentation, no caller-visible schema for what tools return; (3) Weak descriptions on some tools (e.g., 'List all available databases in the database' is circular); (4) Missing parameter descriptions on critical fields (indexSpec, pipeline, filter, update lack detail on format/constraints); (5) No error handling guidance or recovery hints in descriptions; (6) Destructive operations (deleteOne, dropIndex) lack confirmation or dry-run patterns. The tool set is well-structured with a clean BaseTool abstraction and consistent error handling at the implementation level, but the MCP-facing schemas and descriptions need strengthening for LLM selection and safe operation.
Execute a MongoDB aggregation pipeline
Count documents in a collection using MongoDB query syntax
Create a new index on a collection
Delete a single document from a collection
Drop an index from a collection
Query documents in a collection using MongoDB query syntax
List indexes for a collection
listDatabases description is circular: 'List all available databases in the database', grammatically unclear and unhelpful to LLM selection. Should state what data is returned and when to use it before other discovery tools.
Missing or vague parameter descriptions for critical fields: 'filter', 'update', 'pipeline', and 'indexSpec' lack detail on expected format, constraints, or examples. LLMs cannot infer MongoDB query syntax from bare names. Should specify 'MongoDB query object with operators like {$eq, $gt, $in}' or link to MongoDB docs.
No output schema documented. Callers cannot see what fields tools return (e.g., does 'find' return {documents: [], count: N} or raw array?). Without output schemas, LLMs cannot plan downstream tool calls or extract chaining IDs. Pattern baseline: 100% of A+ tools document return types.
| Scored | Grade | Overall | Spec posture | Rubric |
|---|---|---|---|---|
| 2026-09-22 | F | 49 | 2026-07-28+ | v2 |
| 2026-03-09 | D | 50 | - | v1 |
Insert a single document into a collection
List all available collections in the database
List all available databases in the database
Update multiple documents in a collection
Update a single document in a collection
Destructive operations (deleteOne, dropIndex) lack confirmation or dry-run safeguards. Agents make mistakes, a destructive tool should either require explicit confirmation or offer a preview before execution. Pattern: confirmation-request.
Error handling in tool descriptions provides no recovery guidance. When find() returns zero results or deleteOne() fails, the error text does not guide the LLM toward next steps. Pattern baseline: error responses must tell the LLM what to do next.
Missing database context for index tools: createIndex and dropIndex do not accept a 'database' parameter, only 'collection'. This forces LLMs to assume the active/default database, ambiguous and error-prone if multiple databases exist. Should accept both database and collection for clarity.
Pipeline parameter in aggregate tool is typed as 'string' with description 'array of JSON objects'. This is a type mismatch, pipeline should be 'array' or 'object' in schema, not 'string'. LLMs will be confused whether to pass a JSON string or an array.
Missing validation constraints in descriptions: 'limit' in find() has min/max (1-1000) in schema but no description of why or what happens if exceeded. 'projection' accepts any object but should document MongoDB projection syntax (1 to include, 0 to exclude). LLMs need explicit guidance.