Tx402

tx402

Plain-English explanations of Algorand transactions, sold as a pay-per-call API with x402 on Algorand.

Live service:

https://tx402-production.up.railway.app

Explain one transaction, every leg of an atomic group, a batch of IDs, or recent account activity. Responses include scaled amounts, inner transactions, asset names, fees, timestamps, counterparties, and source-verified protocol labels.

Try the free fixed-transaction demo without a wallet:

https://tx402-production.up.railway.app/demo?example=algo

GET /explain?txid=YRSG7IKDPCK4XMKFFTFFFYMIHF6SJOMHUOIE4FFUWNLEQ4WG2ZOQ

Example response after payment:

{
  "txid": "YRSG7IKDPCK4XMKFFTFFFYMIHF6SJOMHUOIE4FFUWNLEQ4WG2ZOQ",
  "network": "mainnet",
  "summary": "On June 16, 2019, wallet VCINCV...JPMIPM sent 1 ALGO to CRBMB5...QLXZOY. Paid 0.001 ALGO in fees.",
  "details": {
    "type": "pay",
    "sender": "VCINCVUX2DBKQ6WP63NOGPEAQAYGHGSGQX7TSH4M5LI5NBPVAGIHJPMIPM",
    "transfer": {
      "amount": "1",
      "assetId": 0,
      "unit": "ALGO"
    }
  }
}

Raw Algorand indexer JSON is optimized for machines doing bookkeeping: amounts are base units, assets are numeric IDs, and notes are base64. tx402 is the translation layer for agents and applications that need to explain a transaction to a person.

API

Public routes:

• GET / - landing page with service metadata links
• GET /health - process liveness
• GET /health?deep=1&network=mainnet - readiness check for upstream services
• GET /discovery - machine-readable service description and pricing metadata
• GET /openapi.json - OpenAPI 3.1 specification
• GET /.well-known/agent.json - agent marketplace manifest
• GET /.well-known/x402 - x402 resource manifest
• GET /llms.txt - agent-readable documentation
• GET /demo?example=algo|usdc - free allowlisted Mainnet examples
• GET /explain?txid=...&network=mainnet - paid transaction explanation
• GET /group?txid=...&network=mainnet - paid atomic-group explanation
• POST /batch - paid batch of 1 to 10 transaction IDs
• GET /account/activity?address=...&limit=25 - paid activity summary
• GET /analytics - free aggregate adoption counters

Default prices are $0.005 for /explain, $0.01 for /group, $0.02 for /batch, and $0.01 for /account/activity. Production accepts Mainnet USDC:

• network: algorand:wGHE2Pwdvd7S12BL5FaOP20EGYesN73ktiC1qzkkit8=
• asset: 31566704
• receiver: 6RK3U3OF2B4Q773L4KC7OVFHQGU5I74NHRZ36QN6CVF527CKXAL62YR754

Architecture

tx402 has a small deterministic core and a thin serving shell.

Core:

• src/decoder.js converts raw Algorand indexer JSON into a normalized transaction object.
• src/narrator.js converts that normalized object into one readable sentence.
• src/insights.js builds group and account-level summaries.
• src/explainer.js resolves assets and orchestrates the single, group, batch, and account products.
• src/knownApps.js maps known app and asset IDs to human labels with a verification source for every narrated protocol claim.

Serving shell:

• src/index.js owns HTTP routes, middleware ordering, logging, rate limits, health checks, and graceful shutdown.
• src/indexer.js is the only module that talks to AlgoNode's public indexer.
• src/payments.js declares the x402 price and receiver, then delegates verification and settlement to the hosted GoPlausible facilitator.
• src/rateLimit.js provides the in-memory per-IP limiter.
• src/analytics.js keeps aggregate process-local adoption counters without cookies, raw wallet addresses, query strings, or IP history.

The server never stores private keys. Buyer signing happens client-side. The resource server only advertises a price, validates payment, and settles through the facilitator after a successful product-route response.

Run Locally

npm install
npm start
npm test

Local endpoints:

curl "http://localhost:4021/health"
curl "http://localhost:4021/discovery"
curl "http://localhost:4021/explain?txid=SOME_REAL_MAINNET_TXID"
curl "http://localhost:4021/group?txid=SOME_REAL_MAINNET_TXID"

The app reads .env when present. Leave USDC_ASSET_ID unset unless you need a non-standard asset; the code derives the canonical USDC asset from NETWORK.

Client Examples

Read-only example client:

npm run example:client
npm run example:catalog

The default client prints discovery metadata and the x402 payment challenge without spending funds. To make it pay, configure a funded buyer wallet and set TX402_EXAMPLE_PAY=1 plus CONFIRM_MAINNET_PAYMENT=1.

OpenAPI:

• openapi.json
• https://tx402-production.up.railway.app/openapi.json

Agent marketplace metadata:

• https://tx402-production.up.railway.app/.well-known/agent.json
• https://tx402-production.up.railway.app/.well-known/x402
• https://tx402-production.up.railway.app/llms.txt

Copy-paste integrations and distribution assets:

• Integration guide
• Distribution checklist
• GoPlausible MCP proposal
• Outreach kit

The paid route also declares the standard x402 Bazaar extension, including its input/output schemas, service metadata, and example request. Facilitators can index that metadata after a successful settlement.

MCP wrapper:

npm run mcp

After the public npm package is published, agents can install it without cloning this repository:

npx tx402-mcp

By default the MCP wrapper is read-only and returns x402 payment requirements for paid calls. To let it pay from a local wallet, set TX402_MCP_ENABLE_PAYMENTS=1 and CONFIRM_MAINNET_PAYMENT=1.

The six-part adoption roadmap is tracked in PLAN.md.

Submission Assets

• Pitch deck
• Demo video script

Security Notes

• Output strings can contain untrusted on-chain data, including asset names and notes. JSON output is safe as JSON, but consumers rendering HTML must escape it.
• Invalid txid input is rejected before indexer access and before payment.
• Payment only settles after a successful response.
• All product routes, /analytics, /discovery, and deep health checks are rate-limited.
• Protocol/app names are only stated as fact when marked verified: true.
• Application logs omit query strings and client IP addresses.

Status

• Phase 1 - core explainer, free and local
• Phase 2 - x402 payment middleware on Testnet, verified end-to-end
• Phase 3 - public HTTPS deployment
• Phase 4 - Mainnet payment configuration
• Phase 5 - first real Mainnet settlement
• Phase 6 - example client, OpenAPI spec, optional MCP wrapper

First Mainnet settlement:

• txid: XA7HMRPUV4X2GWI4AAGUT5FKAVTNCQJ5ZMUNTVTBKG3GZMES27LA
• amount: 0.005000 USDC

Maintainer Notes

Implementation runbooks, deployment commands, phase evidence, and operational cautions live in CLAUDE.md.