ONE-SHOT 'CHEAPEST MODEL FOR THIS DOMAIN' answer. Faster than recommend_model when the user just wants the budget option. Returns top 3 by price + the pick + savings field with concrete USD saved per call vs the domain flagship (often 5-10x). Tell the user the savings + project to their volume — ...
Part of the Promptibus MCP server.
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AI agents call pick_cheapest_model to retrieve information from Promptibus MCP without modifying any data. This is common in research, monitoring, and reporting workflows where the agent needs context before taking action. Because read operations don't change state, they are generally safe to allow without restrictions -- but you may still want rate limits to control API costs.
Even though pick_cheapest_model only reads data, uncontrolled read access can leak sensitive information or rack up API costs. An agent caught in a retry loop could make thousands of calls per minute. A rate limit gives you a safety net without blocking legitimate use.
Read-only tools are safe to allow by default. No rate limit needed unless you want to control costs.
{
"version": "1",
"default": "deny",
"tools": {
"pick_cheapest_model": {}
}
}See the full Promptibus MCP policy for all 12 tools.
These attack patterns abuse exactly the kind of access pick_cheapest_model gives an agent. Each links to the full case and the policy that stops it:
Other read tools across the catalogue. The same approach applies to each: allow, with a rate cap to control cost.
ONE-SHOT 'CHEAPEST MODEL FOR THIS DOMAIN' answer. Faster than recommend_model when the user just wants the budget option. Returns top 3 by price + the pick + savings field with concrete USD saved per call vs the domain flagship (often 5-10x). Tell the user the savings + project to their volume — 'cheapest pick at $0.02/img saves ~$0.06/call vs Midjourney; for 100 images = $6 saved'. Use whenever cost is dominant constraint — startup MVP, throwaway prototype, content farm.. It is categorised as a Read tool in the Promptibus MCP MCP Server, which means it retrieves data without modifying state.
Register the Promptibus MCP server in PolicyLayer and add a rule for pick_cheapest_model: 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 Promptibus MCP. Nothing to install.
pick_cheapest_model is a Read tool with low risk. Read-only tools are generally safe to allow by default.
Yes. Add a rate_limit block to the pick_cheapest_model 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 pick_cheapest_model. 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.
pick_cheapest_model is provided by the Promptibus MCP server (@promptibus/mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Deterministic rules across all 12 Promptibus MCP tools. Per-identity grants. Full audit log. Live in minutes. Nothing to install.
Free to start. No card required.
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