Returns unique values for a specified MongoDB field, with optional filtering and collation, capped at 5000 results for schema discovery and data inspection.
Distinct values of a field (optionally within a filter). Returns at most 5000 values. collation: {"locale": "tr", "strength": 2} for Turkish case-insensitive matching (İ=i, I=ı).
| Name | Required | Description | Default |
|---|---|---|---|
| field | Yes | ||
| filter | No | ||
| database | No | ||
| collation | No | ||
| collection | Yes | ||
| connection | No |
Changes observed during successful MCP inspections.
v1.0.0Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare read-only, idempotent, non-destructive behavior with openWorldHint=false. The description adds a useful operational limit ('at most 5000 values'), which is not in annotations, but does not cover permissions, error behavior, or return format.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
The description is short and front-loads the core purpose and result cap before the collation example. The collation detail is useful but slightly idiosyncratic; overall it is efficient with little wasted text.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
For a read-only tool with no output schema, 6 parameters, and 0% schema coverage, the description provides some essential context (field, filter, collation, result cap). However, it omits database/connection/collection usage and does not clarify output shape or pagination behavior beyond the 5000-value cap.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema description coverage is 0%, so the description must carry the burden. It meaningfully explains field, filter, and collation (with a concrete Turkish example), but leaves database, connection, and collection semantics unaddressed.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description clearly states the tool returns distinct values of a field, optionally filtered, which is a specific verb+resource. It does not explicitly differentiate from siblings like find or aggregate, but the operation is clear enough to distinguish.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
The description implies usage via 'optionally within a filter' but gives no explicit guidance on when to use this tool versus find, aggregate, or count_documents. There are no exclusions or alternatives named.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.