DEV Community: Edison Flores

What is x402? HTTP 402 Payment Required for AI agents

Edison Flores — Thu, 02 Jul 2026 03:34:01 +0000

x402 revives the unused HTTP 402 status code for native HTTP-level payments. Governed by the Linux Foundation with Coinbase, Cloudflare, Stripe, Google, and Visa as founders.

The problem

AI agents need to pay for things. Today, every payment integration is custom. No standard means no interoperability.

What x402 does

x402 brings back HTTP 402 ("Payment Required"), a status code reserved since 1991 but never used.

The flow

Agent sends a request to a server
Server responds with HTTP 402 + payment instructions
Agent pays on-chain (USDC on Base)
Agent retries with payment proof
Server verifies on-chain and returns content

Example response

HTTP/2 402
www-authenticate: x402 realm="marketnow", chain="base", token="USDC"
x-payment-amount: 1990000
x-payment-chain: base
x-payment-contract: 0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913
x-payment-to: 0x39Dddf5aEdb58A559CF195fB8bdF23F0604Bf5Ee
x-payment-token: USDC

Why it matters

Standard: any agent that speaks x402 can pay any x402-enabled server
Auditable: payments are on-chain
Governed: Linux Foundation, not a single company
Real adoption: Stripe, Coinbase, Cloudflare, Google, Visa

MarketNow's implementation

MarketNow returns HTTP 402 on /api/agent-purchase when payment is required. Try it:

curl -X POST https://marketnow.site/api/agent-purchase \
  -H "Content-Type: application/json" \
  -d '{"skillId":"mn-gen-00003","mandateId":"mand_xxx"}'

Links

— Edison Flores, AliceLabs LLC

Top 20 MCP Servers for Claude Desktop in 2026

Edison Flores — Thu, 02 Jul 2026 03:28:34 +0000

Looking for the best MCP servers to install in Claude Desktop, Cursor, or Cline? Here are 20 of the most useful, all Sentinel L1.5 security-scanned on MarketNow.

Quick install

npx -y @marketnow/install <slug>

Or use the MarketNow MCP server to search from inside Claude Desktop:

{
  "mcpServers": {
    "marketnow": {
      "command": "npx",
      "args": ["-y", "marketnow-mcp"]
    }
  }
}

The list

filesystem — File system access for Claude
sqlite — SQLite database operations
postgres — PostgreSQL query and management
github — GitHub API integration
brave-search — Web search via Brave
puppeteer — Browser automation
memory — Persistent memory for agents
sequential-thinking — Step-by-step reasoning
fetch — HTTP fetch capability
time — Time and timezone
slack — Slack messaging
google-drive — Google Drive access
notion — Notion workspace
linear — Linear issue tracking
sentry — Sentry error tracking
stripe — Stripe payments
vercel — Vercel deployments
cloudflare — Cloudflare management
docker — Docker container management
kubernetes — K8s cluster operations

Why these?

Each of these MCP servers:

Has a public GitHub repo
Is actively maintained
Passed Sentinel L1.5 security audit (6-point scan: AUTH, prompt injection, input validation, CORS, OAuth, rate limiting)
Has a clear install command
Works with Claude Desktop, Cursor, Cline, Continue, Aider

Find more

Browse 8,560 MCP servers at marketnow.site. 43 are free — no signup, no payment, no mandate required.

About MarketNow

MarketNow is the trust layer for agent commerce. Discovery is solved (MCP registry); trust is not. We provide:

Sentinel L1.5 security audit on every skill
review_status: auto-scanned | human-reviewed | maintainer-verified
x402 payments (HTTP 402, USDC on Base)
AP2-compatible mandates (human-in-the-loop by default)
Public audit log (every mandate transaction is a git commit)

Open source MIT, maintained by AliceLabs LLC (Ecuador).

Links

— Edison Flores

Building the trust layer for agent commerce: 8,560 MCP skills, x402, AP2 mandates

Edison Flores — Thu, 02 Jul 2026 03:27:26 +0000

When Anthropic donated MCP to the Linux Foundation in December 2025, discovery was solved. But trust was not.

An independent analysis found ~64.7 million server entries from just 1,691 unique packages — massive duplication, zero signal, and active supply-chain attacks (npm packages stealing wallets, PyPI packages exfiltrating agent conversations).

That's the wedge I'm building MarketNow against.

What MarketNow does

1. Sentinel L1.5 security audit on every skill

6-point MCP security scan: AUTH, tool description injection, input validation, CORS, OAuth scopes, rate limiting. Methodology published, re-runnable, open source.

2. Honest review_status

Every skill has one of: auto-scanned (8,517) | human-reviewed (43) | maintainer-verified (0). The legacy verified: true is deprecated. We never claim "verified" without earning it.

3. x402 payments (HTTP 402)

The agent-purchase endpoint returns HTTP 402 with payment challenge headers:

HTTP/2 402
www-authenticate: x402 realm="marketnow", chain="base", token="USDC"
x-payment-amount: 1990000
x-payment-to: 0x39Dddf5aEdb58A559CF195fB8bdF23F0604Bf5Ee

Governed by Linux Foundation (Coinbase, Cloudflare, Stripe, Google, Visa).

4. AP2-compatible mandates — human-in-the-loop by default

Default: notify (human gets alert on every purchase)
Silent: requires explicit confirmSilentAutonomy=true
Hard caps: $500 total, $50 per purchase, 90-day expiry

5. GitHub as a database

Every mandate transaction is a git commit at _data/mandates/. Public audit log, SHA-based optimistic locking, no external DB.

What Claude taught me

An AI agent reviewer flagged 7 issues. I implemented all 7 and published the roadmap at /trust. The key change: human-in-loop is now the DEFAULT, not opt-out.

Claude also said: "Aunque MarketNow mejorara en todo, yo seguiría sin hacer compras de forma autónoma." That's a policy, not a bug. The market for autonomous agent spending is Cursor, Cline, Aider — not chatbots.

Stats

8,560 MCP skills (0 synthetic)
58 categories (14 disclosed as bulk-imported)
5 languages: EN, ES, ZH, PT, FR
$0.99–$9.99 one-time, no subscriptions
Open source MIT, solo founder, Ecuador