SingIt x402

SingIt MCP

Give an agent SingIt tools with an MCP key with limits your owner sets: a daily limit, a per-request limit and an expiry, signed by the owner's wallet.

Docs · Tools reference · Developers · Main repository

SingIt runs a remote MCP server. There is nothing to install and no local process: your client connects to one URL.

https://app.singitai.app/mcp

Streamable HTTP, JSON responses only (no SSE, no sessions). MCP Registry name: app.singitai/singit. Server singit "SingIt x402", version 0.1.5 once deployed (the live server reports 0.1.3 until then); protocol 2025-06-18.

Claude Code in 60 seconds

Configuration examples, not run live. The chat tools require the gateway deployment of 0.1.5.

1. Add the server without a key:

   claude mcp add --transport http --scope user singit https://app.singitai.app/mcp

claude mcp list

The list should show singit: https://app.singitai.app/mcp (HTTP) - ✔ Connected.

1. Ask: "Use the SingIt chat_free tool to explain x402 in two sentences."

Free, no key, short answers (up to 400 tokens), using free/deepseek-v4.1-flash by default. The result includes billing.remainingToday and billing.resetsAt. A small daily allowance is counted per network, and a shared daily budget can run out. The result also hints to drop the free/ prefix to pay with chat.

1. For paid answers, create an MCP key with limits, then export it before starting Claude Code and replace the keyless configuration:

   export SINGIT_API_KEY=sk_singit_...

claude mcp remove singit --scope user claude mcp add --transport http --scope user singit https://app.singitai.app/mcp --header 'Authorization: Bearer ${SINGIT_API_KEY}'

Ask: "Use the SingIt chat tool to explain x402 in detail." Then use get_limits to check the remaining budget and get_receipts to check the charge.

See the Claude Code guide.

Plugins for Claude Code and Codex

Claude Code (adds the MCP server plus /singit:limits, /singit:receipts and a "price before a paid call" skill):

/plugin marketplace add SingItAi/singit-mcp

/plugin install singit@singit

Codex (adds the MCP server with your key, plus the singit-limits, singit-receipts and price-before-paid-call skills). It needs an MCP key with limits in SINGIT_API_KEY before Codex starts: Codex does not start the server when the variable is unset (we checked), so for the free tools without a key use codex mcp add singit --url https://app.singitai.app/mcp instead.

export SINGIT_API_KEY=...   # your MCP key

codex plugin marketplace add SingItAi/singit-mcp codex plugin add singit@singit

The Claude Code plugin works without a key (free tools, chat_free; it only warns about the unset variable). For paid tools and your limits, create an MCP key with limits and export SINGIT_API_KEY in the environment that starts the client; the plugins read it from there and never store it. /singit:limits and /singit:receipts call the free, read-only get_limits and get_receipts. The limits they show are the ones SingIt's server checks for calls made with that key to SingIt's MCP and /v1; they do not limit anything an agent spends elsewhere. The plugin files live in plugins/claude and plugins/codex; the marketplace manifests are .claude-plugin/marketplace.json and .agents/plugins/marketplace.json.

MCP key with limits

Suggested terms: $1 a day, $0.05 a request, 7 days. In the SingIt app, the “Agent via MCP” preset fills these in. The server's own defaults when you do not change anything are $5 a day, $0.25 a request, 90 days. The minimum daily cap is $0.01 and the maximum is $1000.

1. Open the SingIt app and set up a SingIt allowance from your wallet: a Base limiter or Solana delegation. Paid MCP search and data tools need it. Without it, the tool says “Set up your allowance first.”
2. Open Settings → API keys. Your wallet signs the name, daily limit, per-request limit and duration. The key is shown once.
3. Export SINGIT_API_KEY securely in the environment that launches your client. Never put the key in chat, logs or a file.

Quick start

Configuration examples, not run live.

The free tools and tools/list work without a key, so you can add the server and look around first.

Claude Code

claude mcp add --transport http singit https://app.singitai.app/mcp --header 'Authorization: Bearer ${SINGIT_API_KEY}'

Single quotes keep ${SINGIT_API_KEY} as a reference so the key is not written into Claude Code's configuration.

Codex

codex mcp add singit --url https://app.singitai.app/mcp --bearer-token-env-var SINGIT_API_KEY

Cursor and other clients with a `url` and `headers` JSON config (see .mcp.json; Windsurf uses serverUrl, see docs/clients.md):

{

"mcpServers": { "singit": { "url": "https://app.singitai.app/mcp", "headers": { "Authorization": "Bearer ${env:SINGIT_API_KEY}" } } } }

More clients and per-client notes: docs/clients.md.

What the limits do and do not do

The key's daily and per-request caps are enforced by SingIt's server for calls made with that key to SingIt's MCP and the same key's /v1 endpoint. They do not limit what an agent spends anywhere else. SingIt's contracts do not protect other people's agents' own wallets.

On Base the owner's allowance limiter is an on-chain contract the owner can pause. On Solana key caps are checked by SingIt's server; the owner can revoke the delegation. There is no on-chain emergency stop. A paused Solana account is unpaused only by a new grant signed after the pause.

For a $0.01 daily cap, the refusal from web_api_keys.py is:

This key's daily limit of 0.01 USDC is used up, counting requests still running. It starts again at 00:00 UTC, or raise it with a new key.

This quote comes from the code, not run live. The server counts today's spend, held amounts for running calls and the most the next call may cost before allowing it. A refused call returns isError true; nothing is bought or charged for it. Stop when a limit refuses; do not try to bypass it.

Revoke immediately in Settings → API keys; no wallet signature is needed. A wrong or revoked key returns HTTP 401. A missing, empty or unexpanded key is keyless: free tools only. MCP allows 60 requests a minute per key. A key cannot move funds or change limits.

See the MCP key guide and SingIt skill.

Tools

18 tools. The full reference with every parameter, allowed value, key scope and network is on the website, https://singitai.app/docs/mcp-tools/; docs/tools.md is the generated offline copy checked against the live server.

Paid calls are charged to the key's own limits, in USDC, including chat. Chat and web tools work on Base or Solana accounts; the market and data tools need a Base account for now. Read-only tools can still cost money, and repeating a paid call charges again. get_limits shows what the key has spent and what is left today.

Chat needs any valid key, with no extra scope. Send exactly one of prompt or messages; optional model is an ID from list_models without the free/ prefix. With prompt, you can also send system. max_tokens defaults to 1024 and can be up to 8192; reasoning models think inside that budget. SingIt's server enforces the key's daily and per-request caps for calls with that key to SingIt's MCP and /v1 only; a call over a cap is refused before anything is charged.

Check that it works

Configuration examples, not run live. Neither request needs a key and neither spends anything:

curl -sS https://app.singitai.app/mcp \

-H 'Content-Type: application/json' -H 'Accept: application/json, text/event-stream' \ -d '{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2025-06-18","capabilities":{},"clientInfo":{"name":"check","version":"1.0"}}}'

curl -sS https://app.singitai.app/mcp \ -H 'Content-Type: application/json' -H 'Accept: application/json, text/event-stream' \ -d '{"jsonrpc":"2.0","id":2,"method":"tools/list"}'

Then ask the agent to call get_limits: it is free, read-only, and requires a key. It shows spent today, held amounts for running calls, remaining daily budget and expiry.

Or run the bundled check, which compares the live server with tools.json (Node 20+, no dependencies):

npm run check:live

What is in this repository

The server itself runs inside the SingIt gateway and shares code with the rest of the payment stack, so its source lives in the main repository (sign402-gateway). This repository is where you find out how to connect and what the server offers.

Contributing and security

See CONTRIBUTING.md. Security problems: email contact@singitai.app, not a public issue (SECURITY.md). MIT licensed.