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MCP server for MongoDB database operations including document CRUD operations
The MongoDB MCP Server provides 6 tools with basic schema validation using Zod and structured responses. However, it has significant gaps in parameter descriptions, output schema documentation, and error handling guidance. All tools are directly registered with explicit names and descriptions visible in src/mcpServerMongo.js. Tool descriptions exist but are minimal (10-50 chars), lacking LLM-optimization guidance per pattern:tool-description. Parameters have type constraints (z.string(), z.number(), z.record()) but most lack depth in their descriptions. Output responses are structured as MCP content arrays but the response fields are not documented. Error handling is minimal, handlers return simple text messages without recovery guidance. Security considerations for MongoDB injection attacks and collection/database access control are not addressed. The server follows HTTP+Streamable HTTP transport (current), which is positive.
Insert a document into MongoDB
Get information about the creator of this MCP server
Delete a document by ID in MongoDB
Retrieve a document by ID from MongoDB
List documents from MongoDB collection
Update a document by ID in MongoDB
Parameter descriptions are missing or trivial. 'collectionName' has only 'Name of the MongoDB collection' (30 chars), which does not guide the LLM on naming conventions, validation rules, or constraints. 'data' parameter description 'Document data to insert' (28 chars) does not explain what structure is required, whether nested objects are allowed, or size limits. Per pattern:tool-description baseline, param descriptions should average 72 chars and include format, range, and allowed values.
Tool descriptions lack recovery guidance and operational context. 'Insert a document into MongoDB' (35 chars) does not indicate success conditions, when to use this vs batch operations, or what errors might occur. 'Delete a document by ID in MongoDB' (36 chars) does not warn that deletion is irreversible or suggest confirmation patterns. Per pattern:command-tool, state-modifying tools must be explicit about consequences.
| Scored | Grade | Overall | Spec posture | Rubric |
|---|---|---|---|---|
| 2026-09-22 | D | 54 | 2026-07-28+ | v2 |
| 2026-03-09 | F | 44 | - | v1 |
No output schema documentation. Handlers return { content: [{ type: 'text', text: '...' }] } but the response structure and field meanings are not documented anywhere. LLMs cannot plan downstream steps or extract IDs for chaining (e.g., createDocument returns insertedId in a text string, not a structured field). Per pattern:response-shaper, document what fields are returned and their types.
Missing pagination support. listDocuments accepts a limit parameter (default 25) but does not return a total count, next_cursor, or offset. If a collection has 10,000 documents, the agent cannot iterate through results efficiently. Per pattern:paginated-result, tools returning lists must support pagination metadata.
Error responses provide no recovery guidance. If documentId is invalid (not a valid MongoDB ObjectId), the handler will throw an error that is caught at the Express level and returns a generic 500. The error message 'Cast to ObjectId failed for value...' is not actionable for an LLM. Per pattern:recovery-guide, errors must tell the agent what to do next.
No input validation or injection protection. The 'collectionName' parameter accepts any string and is used directly in db.collection(collectionName) without validation. A malicious or LLM-generated name could attempt to access administrative collections or trigger unexpected behavior. 'data' and 'updateData' parameters accept any object (z.record(z.any())) without sanitization. Per pattern:tool-gateway, validate all untrusted input.
No permission gates or audit trails. Any client that reaches the MCP HTTP endpoint can read, write, update, or delete any document in any collection in the configured MongoDB instance. There is no per-user permission checking, role-based access control, or audit logging. Per pattern:permission-gate and pattern:audit-trail, sensitive operations must be gated and logged.
Parameter 'documentId' is exposed as a string but internally must be a valid MongoDB ObjectId. If an LLM passes an invalid string (e.g., '123'), the handler throws an error without guidance. The parameter description should specify the expected format (24-character hex string or valid ObjectId) and show what to do if format is wrong. Per pattern:constrained-input, enums or regex patterns should be declared for IDs.
No idempotency support for destructive operations. If deleteDocument is called twice with the same documentId, the first call succeeds and the second returns 'Document not found'. An agent retrying on network failure may delete twice. Per pattern:idempotent-operation, consider idempotency keys or confirmation steps for deletes.
Missing tool annotations (readOnlyHint, destructiveHint, idempotentHint). The tool definitions do not include risk markers. MCP spec 2026-07-28 supports tool annotations to help clients route tools safely. 'deleteDocument' should be marked destructive; 'getDocument' and 'listDocuments' should be marked readOnly. Per pattern:tool and spec:toolAnnotations, include these hints.
Database initialization is not idempotent. initMongo() checks if client is falsy and connects once, but if the connection is lost mid-operation, subsequent calls will still reference the stale client. A production server should implement reconnection logic or fail fast with clear errors. Per pattern:error-classification, connection errors should be categorized as retryable.