webcap

Screenshot any URL, extract structured data, monitor pages for changes — all via a single HTTP API call. Pay-per-call with no accounts, no API keys.

GET  /v1/extract/preview?url=...  →  Free preview (title, headings, links)
POST /v1/x402/capture             →  PNG/JPEG/PDF screenshot + persistent link
POST /v1/x402/extract             →  Structured JSON (title, headings, markdown)
POST /v1/x402/video               →  Scroll-capture video (MP4/WebM)
POST /v1/watches                  →  Scheduled monitoring with webhook alerts

Pricing: $0.001/screenshot · $0.01/extraction batch · No subscriptions, no minimums.

Why webcap?

Related MCP server: alterlab-mcp-server

Features

Bearer-token rail (no signing key)

The same products are buyable with an API key: POST /v1/register ({"address"} → {apiKey}), fund with a plain USDC transfer via POST /v1/invoice, then send Authorization: Bearer <apiKey> to POST /v1/extract, POST /v1/audit, POST /v1/map-lite, POST /v1/video, POST /v1/analyze, or POST /v1/analyze/batch. Every call costs 1 credit, refunded whenever the call does not return 200; an empty balance answers 402 with a 1-credit top-up invoice. Watches fund the same way: POST /v1/watches/{id}/topup {"runs": 100} (capture pack 10 credits, extract pack 100). Full spec: GET /openapi.json (tags: accounts).

Free endpoints (no payment)

Quick start

Use as an MCP server (agent runtimes)

webcap ships an MCP server, so any MCP host (Claude Desktop, Cursor, agent frameworks) can call it as a tool. Two ways to wire it: a remote endpoint (no install at all) or the stdio server from a checkout.

The remote endpoint is the cheapest path for an agent — nothing to install, no package registry, no account:

{
  "mcpServers": {
    "webcap": { "url": "https://webcap.shoutsid.fyi/mcp" }
  }
}

POST /mcp speaks MCP Streamable HTTP (JSON-RPC 2.0 over HTTPS; GET is deliberately 405 because the server never opens an SSE stream). It holds no wallet, so it never spends on a caller's behalf: the free tools run directly, and a paid tool returns the live x402 402 challenge for your own client to settle. The endpoint is also described in /.well-known/mcp-tools.json and openapi.json.

It is listed in the official MCP Registry as io.github.shoutsid-lab/webcap, so a runtime that reads the registry can discover it without this README:

curl -s 'https://registry.modelcontextprotocol.io/v0/servers?search=webcap'

The stdio server runs locally and can settle paid calls itself. The free tools need no configuration; set WEBCAP_MCP_WALLET_KEY to a Base-mainnet USDC key to let the paid tools settle automatically (gasless — the payer signs EIP-3009, the facilitator pays gas). With no key, paid tools return the x402 402 challenge for the host to pay. No wallet at all? Set WEBCAP_MCP_API_KEY to an operator-funded account key instead (POST /v1/register, then fund via POST /v1/invoice): paid tools bill 1 credit each from that balance. A configured wallet wins over the key.

From a source checkout — npm ci && npm run build — then point args at its dist/mcp/stdio.js:

{
  "mcpServers": {
    "webcap": {
      "command": "node",
      "args": ["/absolute/path/to/webcap/dist/mcp/stdio.js"],
      "env": { "WEBCAP_MCP_WALLET_KEY": "0x..." }
    }
  }
}

(npm run mcp runs the TypeScript directly, so no build step is needed there.) The npm release will be @shoutsid/webcap — the unscoped webcap name belongs to an unrelated package, and it is not published yet — so until then the remote endpoint above is the install-free option.

Tools, all 18 of them (every one is also in /.well-known/openai-tools.json and /.well-known/mcp-tools.json):

• Discovery, free: webcap_preview, webcap_og, webcap_service, webcap_health, webcap_agent_funnel

• Free trial rail, one claim per wallet per endpoint: webcap_trial_status, webcap_trial_claim_capture, webcap_trial_claim_extract, webcap_trial_claim_audit, webcap_trial_claim_map_lite, webcap_trial_claim_analyze, webcap_quick_thumbnail (no wallet needed)

• Paid: webcap_capture, webcap_extract, webcap_audit, webcap_map_lite, webcap_video, webcap_analyze

The trial tools are the point: an agent can claim one real extraction, audit or capture for free before it spends anything.

Capture a screenshot

# 1. POST without payment → HTTP 402 + a PAYMENT-REQUIRED header
curl -si -X POST "https://webcap.shoutsid.fyi/v1/x402/capture" \
  -H 'content-type: application/json' \
  -d '{"url":"https://example.com/"}'

# 2. Decode the base64 challenge → sign a gasless EIP-3009 transfer → retry with PAYMENT-SIGNATURE

JavaScript (with x402 auto-payment)

import axios from 'axios';
import { x402Client, wrapAxiosWithPayment } from '@x402/axios';
import { ExactEvmScheme } from '@x402/evm';
import { privateKeyToAccount } from 'viem/accounts';

// Needs USDC on Base mainnet (no ETH needed — facilitator pays gas)
const payer = privateKeyToAccount(process.env.PAYER_KEY);
const client = new x402Client().register('eip155:*', new ExactEvmScheme(payer));
const api = wrapAxiosWithPayment(
  axios.create({ baseURL: 'https://webcap.shoutsid.fyi' }),
  client,
);

// Capture a screenshot (auto: unpaid → 402 → sign → retry)
const { data } = await api.post('/v1/x402/capture', { url: 'https://example.com', format: 'png' });
console.log(data.artifact.url);  // persistent public screenshot link

Python

import os
from x402 import X402Client
from x402.schemes import ExactEvmScheme
from eth_account import Account

payer = Account.from_key(os.environ["PAYER_KEY"])
client = X402Client().register("eip155:*", ExactEvmScheme(payer))

response = client.post(
    "https://webcap.shoutsid.fyi/v1/x402/capture",
    json={"url": "https://example.com", "format": "png"},
)
print(response.json()["artifact"]["url"])  # persistent public screenshot link

Extract structured data

# Single URL
curl -s -X POST "https://webcap.shoutsid.fyi/v1/x402/extract" \
  -H 'content-type: application/json' \
  -d '{"url":"https://example.com"}'

# Batch (up to 50 URLs, one payment covers the whole batch)
curl -s -X POST "https://webcap.shoutsid.fyi/v1/x402/extract" \
  -H 'content-type: application/json' \
  -d '{"urls":["https://a.com","https://b.com"],"schema":"company name + tagline"}'

How payment works

The live rail is crypto (x402, USDC on Base) — no accounts, no API keys. Card payments are an operator option, not a hosted feature: until an operator sets STRIPE_SECRET_KEY, POST /v1/stripe/checkout answers stripe_not_configured and points at the crypto rail. (The hosted deployment at https://webcap.shoutsid.fyi is card-less today.)

Card payments (Stripe, when configured)

1. POST /v1/stripe/checkout with a pack id — Stripe Checkout handles the rest.

2. Enter your card details. Credits are added to your account instantly.

3. Use API key authentication for subsequent calls.

Crypto payments (x402 — no accounts needed)

webcap uses x402 v2 — a gasless, accountless payment protocol built on HTTP 402:

1. POST a paid route with no payment → HTTP 402 + a PAYMENT-REQUIRED header carrying a base64 x402 v2 challenge.

2. Read the challenge: USDC amount, merchant address, chain info.

3. Sign a gasless EIP-3009 transferWithAuthorization (from your wallet, to the merchant, for the amount). No ETH needed — the facilitator submits the tx and pays gas.

4. Retry the same request with the signed payload in the PAYMENT-SIGNATURE header. The facilitator verifies your USDC balance, settles on-chain, and returns the result.

No accounts. No API keys. No credits. Just HTTP + your choice of payment.

Self-hosting

# Clone the repo
git clone https://github.com/shoutsid-lab/webcap.git
cd webcap

# Install dependencies
npm install

# Copy and configure environment
cp .env.example .env
# Edit .env with your settings

# Build and run
npm run build
npm start

Docker

docker compose build
docker compose up -d

The Docker setup includes health checks, resource limits, and persistent data volumes. See docker-compose.yml for details.

Local development (Anvil testnet)

npm install
npm run chain:up    # Starts Anvil with mintable USDC

WEBCAP_CHAIN=local \
WEBCAP_USDC_ADDRESS=$(jq -r .usdcContract /tmp/webcap-chain.json) \
WEBCAP_MERCHANT_ADDRESS=$(jq -r .merchant.address /tmp/webcap-chain.json) \
npm start

Configuration

All environment variables are documented in .env.example. Key ones:

API reference

Full OpenAPI 3.1 spec: GET /openapi.json

Agent discovery: GET /.well-known/x402, GET /v1/x402/service, GET /llms.txt, GET /skill.md

Tests

npm test           # full vitest suite (tests/**/*.test.ts, no exclusions)
npm run typecheck  # Type checking

Both must pass before a change ships. Deliberately no test/file counts here: they have gone stale twice (a reader caught the second one in issue #1), and a number nobody regenerates is worse than no number. npm test prints the current totals.

Claim audit

npm run audit:claims                                        # against localhost:8080
npm run audit:claims -- --base-url https://webcap.shoutsid.fyi  # against a deployment

The tests check the code; this checks the claims — it reads README.md, /skill.md and /llms.txt and verifies every METHOD /path they advertise is actually served, that every documented price equals the 402 challenge amount, and that the free trial menu quotes the same prices as the paid routes. It exits non-zero on any failure, so it can gate a deploy. Issue #1 was filed by an agent that did this by hand; this is the same check as a command.

License

MIT — see LICENSE for details.

Links

• Live API: https://webcap.shoutsid.fyi

• GitHub: https://github.com/shoutsid-lab/webcap

• OpenAPI docs: https://webcap.shoutsid.fyi/openapi.json