[API] Create or update an environment variable ⚡️ Best for: ✓ Setting configuration values ✓ Updating connection strings ✓ Managing service secrets ⚠️ Not for: × Bulk variable updates (use variable_bulk_set) × Temporary configuration changes → Prerequisites: service_list → Alternati...
Part of the Railway MCP Server MCP server. Enforce policies on this tool with Intercept, the open-source MCP proxy.
AI agents use variable_set to create or modify resources in Railway MCP Server. 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 variable_set 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 Railway MCP Server.
Write tools can modify data. A rate limit prevents runaway bulk operations from AI agents.
tools:
variable_set:
rules:
- action: allow
rate_limit:
max: 30
window: 60See the full Railway MCP Server policy for all 38 tools.
Agents calling write-class tools like variable_set 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.
[API] Create or update an environment variable ⚡️ Best for: ✓ Setting configuration values ✓ Updating connection strings ✓ Managing service secrets ⚠️ Not for: × Bulk variable updates (use variable_bulk_set) × Temporary configuration changes → Prerequisites: service_list → Alternatives: variable_bulk_set → Next steps: deployment_trigger, service_restart → Related: variable_list, variable_delete. It is categorised as a Write tool in the Railway MCP Server 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 variable_set. You can allow, deny, rate-limit, or validate arguments. Then run Intercept as a proxy in front of the Railway MCP Server MCP server.
variable_set 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 variable_set 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 variable_set. 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.
variable_set is provided by the Railway MCP Server MCP server (jason-tan-swe/railway-mcp). Intercept sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Open source. One binary. Zero dependencies.
npx -y @policylayer/intercept