# approve_underlying

Approve the jToken contract to spend your underlying TRC20 tokens.

Agent View of the PolicyLayer registry record for `approve_underlying`. HTML page: https://policylayer.com/tools/justlend-mcp-server-justlend/approve-underlying

## Facts

- Tool: `approve_underlying`
- Server: Justlend (`justlend/mcp-server-justlend`) — https://policylayer.com/tools/justlend-mcp-server-justlend.md
- Homepage: https://github.com/justlend/mcp-server-justlend
- Risk category: Write (Medium risk)
- Registry record: grade F, identity unverified
- Server rate-limited: no
- Parameters: 0
- Recommended policy verdict: Rate-limited

## Example call (MCP tools/call, JSON-RPC 2.0)

```json
{
  "jsonrpc": "2.0",
  "id": 1,
  "method": "tools/call",
  "params": {
    "name": "approve_underlying",
    "arguments": {}
  }
}
```

## 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 own 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."

## Use case

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.

## Recommended policy (PolicyLayer)

Verdict: **Rate-limited**. Enforced by the PolicyLayer MCP gateway (https://policylayer.com/mcp-gateway) before a call reaches Justlend:

```json
{
  "version": "1",
  "default": "deny",
  "tools": {
    "approve_underlying": {
      "limits": [
        {
          "counter": "approve_underlying_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}
```

## Other tools on Justlend (103)

- `return_energy_rental` — Destructive — https://policylayer.com/tools/justlend-mcp-server-justlend/return-energy-rental.md
- `buy_energy_direct` — Financial — https://policylayer.com/tools/justlend-mcp-server-justlend/buy-energy-direct.md
- `claim_rewards` — Financial — https://policylayer.com/tools/justlend-mcp-server-justlend/claim-rewards.md
- `claim_strx_rewards` — Financial — https://policylayer.com/tools/justlend-mcp-server-justlend/claim-strx-rewards.md
- `deposit_jst_for_votes` — Financial — https://policylayer.com/tools/justlend-mcp-server-justlend/deposit-jst-for-votes.md
- `moolah_borrow` — Financial — https://policylayer.com/tools/justlend-mcp-server-justlend/moolah-borrow.md
- `moolah_liquidate` — Financial — https://policylayer.com/tools/justlend-mcp-server-justlend/moolah-liquidate.md
- `moolah_repay` — Financial — https://policylayer.com/tools/justlend-mcp-server-justlend/moolah-repay.md
- `moolah_supply_collateral` — Financial — https://policylayer.com/tools/justlend-mcp-server-justlend/moolah-supply-collateral.md
- `moolah_vault_deposit` — Financial — https://policylayer.com/tools/justlend-mcp-server-justlend/moolah-vault-deposit.md
- `moolah_vault_withdraw` — Financial — https://policylayer.com/tools/justlend-mcp-server-justlend/moolah-vault-withdraw.md
- `moolah_withdraw_collateral` — Financial — https://policylayer.com/tools/justlend-mcp-server-justlend/moolah-withdraw-collateral.md
- `rent_energy` — Financial — https://policylayer.com/tools/justlend-mcp-server-justlend/rent-energy.md
- `repay` — Financial — https://policylayer.com/tools/justlend-mcp-server-justlend/repay.md
- `supply` — Financial — https://policylayer.com/tools/justlend-mcp-server-justlend/supply.md
- `transfer_trc20` — Financial — https://policylayer.com/tools/justlend-mcp-server-justlend/transfer-trc20.md
- `transfer_trx` — Financial — https://policylayer.com/tools/justlend-mcp-server-justlend/transfer-trx.md
- `withdraw` — Financial — https://policylayer.com/tools/justlend-mcp-server-justlend/withdraw.md
- `withdraw_all` — Financial — https://policylayer.com/tools/justlend-mcp-server-justlend/withdraw-all.md
- `withdraw_votes_from_proposal` — Financial — https://policylayer.com/tools/justlend-mcp-server-justlend/withdraw-votes-from-proposal.md
- `withdraw_votes_to_jst` — Financial — https://policylayer.com/tools/justlend-mcp-server-justlend/withdraw-votes-to-jst.md
- `wrap_trx` — Financial — https://policylayer.com/tools/justlend-mcp-server-justlend/wrap-trx.md
- `borrow` — Read — https://policylayer.com/tools/justlend-mcp-server-justlend/borrow.md
- `calculate_energy_rental_price` — Read — https://policylayer.com/tools/justlend-mcp-server-justlend/calculate-energy-rental-price.md
- `check_allowance` — Read — https://policylayer.com/tools/justlend-mcp-server-justlend/check-allowance.md
- `check_jst_allowance_for_voting` — Read — https://policylayer.com/tools/justlend-mcp-server-justlend/check-jst-allowance-for-voting.md
- `check_strx_withdrawal_eligibility` — Read — https://policylayer.com/tools/justlend-mcp-server-justlend/check-strx-withdrawal-eligibility.md
- `claim_moolah_mining_period` — Read — https://policylayer.com/tools/justlend-mcp-server-justlend/claim-moolah-mining-period.md
- `claim_v1_mining_period` — Read — https://policylayer.com/tools/justlend-mcp-server-justlend/claim-v1-mining-period.md
- `estimate_lending_energy` — Read — https://policylayer.com/tools/justlend-mcp-server-justlend/estimate-lending-energy.md
- …and 73 more: https://policylayer.com/tools/justlend-mcp-server-justlend.md

## For agents

This record is a snapshot. Live verdicts and the full registry:

- Check every server in your MCP config at once: `npx -y policylayer stack`
- Vet a server before you add it: install the mcp-precheck skill — `npx skills add https://policylayer.com` (skill text: https://policylayer.com/skill.md)
- Query the registry over MCP: endpoint `https://api.policylayer.com/mcp` — tools `check_mcp_server`, `check_mcp_stack`, `check_tool`, `search_registry`, `get_change_events`

---

Source: the PolicyLayer MCP registry — one continuously verified record per MCP server. Full record: https://policylayer.com/registry?q=justlend-mcp-server-justlend · API: https://policylayer.com/registry/api · Policy library: https://policylayer.com/policies/justlend-mcp-server-justlend