vantic — Claude Code MCP server: spending limits for agents
A signed mandate caps what an agent may pay and who it may pay, and the check runs before money moves. Useful when your agent calls payment APIs.
claude mcp add vantic -- npx -y @vantic/sdkWhat vantic does
Vantic hands your agent a signed mandate: a per-transaction cap, a rolling budget, allowed actions and a counterparty allowlist. The guard sits outside the model and fires before the money-moving code, so a fully compromised agent still cannot spend out of scope. Every permitted action leaves a signed, hash-chained receipt you can verify offline and use as evidence if a charge is disputed.
There are two ways in. The @vantic/sdk library goes into your code — generateKeyPair, issueMandate, AgentWallet — and an existing payment tool can be gated with wrapMcpTool, where a blocked call comes back to the model as a tool error and the real charge never fires. Or run the MCP server with npx vantic-mcp, which exposes stateless verification tools to the host: mandate_authorize, mandate_verify_chain, mandate_verify_credential, mandate_resolve_did. No private keys on the server side.
Identity uses W3C did:key and did:web, and the owner-to-agent link is a Verifiable Credential. There are no dependencies beyond Node's built-in crypto: Ed25519 and SHA-256. This is v0.1. The code is described as production-quality, but it has not been audited and the wire format is not frozen — for real payments, read ROADMAP.md and the threat model in spec/SPEC.md first.
What it helps with
- cap an agent's spend per transaction and per week
- keep an agent from paying counterparties you never approved
- block a payment planted through a prompt injection
- keep a signed action log for a disputed charge
- gate a payment tool you already have without restructuring it
Example prompts for the agent
- Issue the agent a mandate for purchases up to $200 each, limited to
etsy.com - Wrap
purchaseToolwithwrapMcpToolso a blocked call returns as a tool error - Verify the receipt chain for the agent's latest mandate
How to install vantic
Platform CLI
claude mcp add vantic -- npx -y @vantic/sdkPlatform CLI
codex mcp add vantic -- npx -y @vantic/sdkConfig file
{
"mcpServers": {
"vantic": {
"command": "npx",
"args": [
"-y",
"@vantic/sdk"
]
}
}
}Config file
{
"servers": {
"vantic": {
"type": "stdio",
"command": "npx",
"args": [
"-y",
"@vantic/sdk"
]
}
}
}Platform CLI
gemini mcp add vantic npx -y @vantic/sdkStep by step, with commands for each platform: How to add an MCP server to Claude Code, Codex, Cursor, VS Code, Gemini CLI and more
Questions about vantic
How do I install vantic in Claude Code?
Run claude mcp add vantic -- npx -y @vantic/sdk. The server is then available to the host over MCP.
What does vantic do?
It issues the agent a signed mandate with a budget, a per-transaction cap and an allowlist, checks every money-moving call before it executes, and records signed receipts.
Does the MCP server need private keys?
No. It exposes verification tools only; keys stay with the owner and the agent.
