AI agents use set_trial_user_attr to create or update resources in Optuna MCP Server — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Optuna MCP Server environment.
This tool modifies trial attributes within an Optuna study, which is a reversible write operation. It does not delete data (so not Destructive), does not execute arbitrary code (so not Execute), and does not involve financial transactions.
From the tool's definition The tool name 'set_trial_user_attr' and description 'Set user attributes for a trial' indicate it modifies trial metadata/attributes. This is a create/modify operation on existing trial data.
Documented attack patterns abuse exactly the kind of access set_trial_user_attr gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Optuna MCP Server, and nothing reaches the server without passing your rules. This is the rule we recommend for set_trial_user_attr:
{
"version": "1",
"default": "deny",
"tools": {
"set_trial_user_attr": {
"limits": [
{
"counter": "set_trial_user_attr_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}set_trial_user_attr stays usable, but capped — an agent stuck in a loop can't make hundreds of changes a minute. Everything else on the server is denied unless you say otherwise.
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Set user attributes for a trial. It is categorised as a Write tool in the Optuna MCP Server MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Optuna MCP Server MCP server in PolicyLayer and add a rule for set_trial_user_attr: allow, deny, rate-limit, or require approval. Point your MCP client at the PolicyLayer proxy URL and the rule is enforced on every call, before it reaches Optuna MCP Server. Nothing to install.
set_trial_user_attr is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.
Yes. Add a rate_limit block to the set_trial_user_attr rule in your PolicyLayer policy. For example, setting max: 10 and window: 60 limits the tool to 10 calls per minute. Rate limits are tracked per agent session and reset automatically.
Set action: deny in the PolicyLayer policy for set_trial_user_attr. The AI agent will receive a policy violation error and cannot call the tool. You can also include a reason field to explain why the tool is blocked.
set_trial_user_attr is provided by the Optuna MCP Server MCP server (optuna/optuna-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Deterministic rules across all 26 Optuna MCP Server tools. Per-identity grants. Full audit log. Live in minutes. Nothing to install.
Free to start. No card required.
26 Optuna MCP Server tools catalogued and risk-classified — across an index of 42,500+ MCP servers.