set_budget · Agent Cost MCP: Risk & Policy

WHAT IT DOES

What set_budget does on Agent Cost

AI agents use set_budget to create or update resources in Agent Cost — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Agent Cost environment.

WHY IT NEEDS A POLICY

Why set_budget needs a policy

This tool modifies budget configuration settings, which is a reversible write operation. While budget limits relate to financial oversight, the tool itself does not move money, authorize transactions, or commit financial obligations — it only configures thresholds for cost tracking and alerts.

From the tool's definition Tool named 'set_budget' with description 'Set daily and/or monthly budget limits' — creates or modifies configuration data (budget thresholds) that affects financial tracking and spending controls.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

set_budget Rate-limited

set_budget 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.

View as policy code

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "set_budget": {
      "limits": [
        {
          "counter": "set_budget_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

LIMIT THIS TOOL →

Instant setup, no code required.

PolicyLayer is an MCP gateway: every tool call is checked against your rule before it reaches Agent Cost, so you can run agents against it safely.

FAQ

Questions about set_budget

What does the set_budget tool do? +

Set daily and/or monthly budget limits. It is categorised as a Write tool in the Agent Cost MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on set_budget? +

Register the Agent Cost MCP server in PolicyLayer and add a rule for set_budget: 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 Agent Cost. Nothing to install.

What risk level is set_budget? +

set_budget is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.

Can I rate-limit set_budget? +

Yes. Add a rate_limit block to the set_budget 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.

How do I block set_budget completely? +

Set action: deny in the PolicyLayer policy for set_budget. 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.

What MCP server provides set_budget? +

set_budget is provided by the Agent Cost MCP server (vanthienha199/agent-cost-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.