Update an agent's system prompt / instructions. Pass the full new prompt text. Only works for single_prompt agents. Optionally update the first message too. For versioned agents, changes are saved as a draft — use publish_draft to make them live.
Part of the Smallest MCP server. Enforce policies on this tool with Intercept, the open-source MCP proxy.
AI agents use update_agent_prompt to create or modify resources in Smallest. Write operations carry medium risk because an autonomous agent could trigger bulk unintended modifications. Rate limits prevent a single agent session from making hundreds of changes in rapid succession. Argument validation ensures the agent passes expected values.
Without a policy, an AI agent could call update_agent_prompt repeatedly, creating or modifying resources faster than any human could review. Intercept's rate limiting ensures write operations happen at a controlled pace, and argument validation catches malformed or unexpected inputs before they reach Smallest.
Write tools can modify data. A rate limit prevents runaway bulk operations from AI agents.
tools:
update_agent_prompt:
rules:
- action: allow
rate_limit:
max: 30
window: 60See the full Smallest policy for all 70 tools.
Agents calling write-class tools like update_agent_prompt have been implicated in these attack patterns. Read the full case and prevention policy for each:
Other tools in the Write risk category across the catalogue. The same policy patterns (rate-limit, validate) apply to each.
Update an agent's system prompt / instructions. Pass the full new prompt text. Only works for single_prompt agents. Optionally update the first message too. For versioned agents, changes are saved as a draft — use publish_draft to make them live.. It is categorised as a Write tool in the Smallest MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Add a rule in your Intercept YAML policy under the tools section for update_agent_prompt. You can allow, deny, rate-limit, or validate arguments. Then run Intercept as a proxy in front of the Smallest MCP server.
update_agent_prompt 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 update_agent_prompt rule in your Intercept 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 Intercept policy for update_agent_prompt. 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.
update_agent_prompt is provided by the Smallest MCP server (@developer-smallestai/smallest-mcp-server). Intercept sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Deterministic policy on every MCP tool call. Per-identity grants. Full audit log.