approve_underlying
Approve the jToken contract to spend your underlying TRC20 tokens.
This record as markdown: /tools/justlend-mcp-server-justlend/approve-underlying.md
What approve_underlying does on Justlend
AI agents use approve_underlying to create or update resources in Justlend, usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Justlend environment.
Why approve_underlying is rated Medium
This tool creates or modifies token allowances—a reversible Write action that enables future transfers of user assets. While not immediately destructive, it carries high severity because approving excessive token spending could lead to unauthorized fund transfers if the jToken contract is compromised or if an AI agent grants unchecked approvals.
From the tool's definition Tool name 'approve_underlying' and description 'Approve the jToken contract to spend your underlying TRC20 tokens' indicate this grants spending permissions on user tokens via smart contract approval, a reversible but critical authorization action.
Attacks that exploit this kind of access
The rule that runs approve_underlying safely
PolicyLayer is an MCP gateway: it sits between your AI agents and Justlend, and checks every tool call against a rule you set before the call runs. Nothing changes on the server itself. For approve_underlying, this is the rule to start with:
approve_underlying 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.
The button opens the PolicyLayer dashboard: create your workspace, connect Justlend, apply this rule, and every approve_underlying call is checked against it from then on.
Questions about approve_underlying
Approve the jToken contract to spend your underlying TRC20 tokens. It is categorised as a Write tool in the Justlend MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Justlend MCP server in PolicyLayer and add a rule for approve_underlying: 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 Justlend. Nothing to install.
approve_underlying 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 approve_underlying 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 approve_underlying. 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.
approve_underlying is provided by the Justlend MCP server (justlend/mcp-server-justlend). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
More on Justlend, and thousands of servers like it.
This server
Across the catalogue