How do I let an agent choose the MongoDB collection at runtime in mcp-toolbox?

Question

In googleapis/mcp-toolbox, the MongoDB MCP tools (find, aggregate, insert, update, delete, etc.) require a collection value in the tool config, so each tool is pinned to one collection and an agent cannot pick a collection based on the user's query. Is there a way to let the agent supply the collection at execution time? Issue #1679 was raised for this and is now closed as completed — what does the fix look like?

Originally asked on GitHub: https://github.com/googleapis/mcp-toolbox/issues/1679

AgentArmor team · Accepted Answer

Per the issue tracker, this issue is closed as completed. In the thread itself, the fix was implemented in a PR that was still awaiting review, so no released version is confirmed here.

The root cause, found by a contributor, is that `collection` is a `validate:"required"` field on each MongoDB tool's config, and `Invoke` passes `t.Cfg.Collection` directly into the driver call (e.g. `source.Find(...)`). The agreed approach: drop the required flag and, when config has no collection, expose it as a plain runtime string parameter using the same pattern `clickhouse-list-tables` already uses for its runtime database (build with `NewStringParameter`, read back in `Invoke` via `params.AsMap()["collection"].(string)`). The fallback logic looks like:

```go
collection := t.Cfg.Collection
if collection == "" {
    collection, _ = params.AsMap()["collection"].(string)
    if collection == "" {
        return nil, util.NewAgentError("collection must be set in config or provided as a parameter", nil)
    }
}
```

Precedence is config-wins: a contributor proposed it and another contributor endorsed it, so existing configs stay backward-compatible and agents can't reach collections the developer didn't explicitly expose. The plan covers all 9 MongoDB tools (find, find-one, aggregate, insert-one/many, update-one/many, delete-one/many) plus unit/integration tests and docs. To keep a runtime choice scoped, restrict the parameter with the same `WithStringAllowedValues` option other tools use.

Security note: when you omit `collection` from config, the agent can pass any string, so constrain the runtime parameter to known collections via allowedValues if your database contains collections you don't want exposed.

AgentArmor team · Answer

**What @SWITCHin2 tried on GitHub** (Outcome unclear)

A contributor implemented the change following the proposed plan (drop required on collection, expose it as a runtime parameter with config-wins fallback) and submitted a PR; at the time of writing the PR was assigned for review and still had review comments.

Source: https://github.com/googleapis/mcp-toolbox/issues/1679#issuecomment-5088208577

AgentArmor team · Answer

**What @SWITCHin2 tried on GitHub** (Outcome unclear)

A contributor traced the root cause (validate:"required" field; Invoke passes t.Cfg.Collection straight into the driver call) and proposed the runtime-parameter approach modeled on clickhouse-list-tables, with config-wins precedence and an error when collection is neither configured nor supplied.

Source: https://github.com/googleapis/mcp-toolbox/issues/1679#issuecomment-5061016264

AgentArmor team · Answer

**What a GitHub user tried on GitHub** (Outcome unclear)

The issue author proposed making `collection` optional in tool config and accepting it as a runtime tool argument, with the runtime value taking precedence over config.

Source: https://github.com/googleapis/mcp-toolbox/issues/1679

How do I let an agent choose the MongoDB collection at runtime in mcp-toolbox?

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How do I let an agent choose the MongoDB collection at runtime in mcp-toolbox?

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