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#26 • Part 4 • 2025-09-25 • 25 min

The 8-Chain Testnet Ecosystem: When One Blockchain Isn't Enough

How we built a unified testing environment across 8 blockchains—and discovered that cross-chain development is a whole different game

testnet ecosystem multi-chain infrastructure

Part 4 of the Journey: Advanced Topics & Deep Dives Previous: The Bloomberg Terminal Rescue

The 8-Chain Testnet Ecosystem: When One Blockchain Isn’t Enough

How we built a unified testing environment across 8 blockchains—and discovered that cross-chain development is a whole different game

Date: October 7, 2025 (Story from September 16, 2025) Author: Myron Koch & Claude Desktop Category: Blockchain Infrastructure

The Problem Nobody Talks About

September 16, 2025. I’m debugging an arbitrage opportunity that exists across three chains: Ethereum, Polygon, and BNB Chain.

The opportunity is real: USDC is trading at $1.002 on Ethereum, $0.998 on Polygon. After fees, it’s profitable. But to test it, I need to:

  1. Check balances on Ethereum
  2. Check balances on Polygon
  3. Check balances on BNB Chain
  4. Estimate fees on all three
  5. Simulate the trade
  6. Execute if profitable

Each chain has different tools. Different servers. Different terminal windows. Different authentication. I’m switching contexts constantly, losing track of which chain I’m on, which wallet has funds, what the current gas prices are.

By the time I’ve checked everything, the arbitrage opportunity is gone.

The realization: We can’t build real cross-chain applications if testing across chains is this painful.

The Vision (Or: What I Scribbled on a Whiteboard)

I open a new document. The idea is simple but ambitious:

One unified interface
↓
All 8 major blockchain architectures
↓
All accessible through natural language
↓
All working together seamlessly

Not just “multiple servers running.” True interoperability. One conversation that can:

All in the same session. All through Claude Desktop. All feeling like they’re part of the same ecosystem.

The technical challenge: Make 8 completely different blockchain architectures—EVM, UTXO, Cosmos SDK, Solana—feel like one unified system.

Choosing the Battleground: Which 8 Chains?

The Selection Criteria

Not just “popular chains.” We needed to cover every major blockchain architecture pattern:

1. Ethereum Sepolia - The EVM reference

2. Bitcoin Testnet - The UTXO reference

3. Polygon Mainnet - The high-throughput EVM

4. Arbitrum Mainnet - The L2 scaling solution

5. Avalanche C-Chain - The alternative EVM

6. Cosmos Hub - The inter-chain ecosystem

7. BNB Chain - The DeFi powerhouse

8. Solana Testnet - The performance monster

Eight chains. Four completely different architectures. One unified interface.

Phase 1: The EVM Foundation (Hours 0-8)

September 16, 6 PM

I start with what I know: Ethereum.

The Ethereum Sepolia server already exists. It’s battle-tested. 19/19 tests passing. It works.

But “working in isolation” isn’t the same as “working in an ecosystem.”

New requirements:

I add a get_chain_info tool:

async function getChainInfo() {
    const blockHeight = await provider.getBlockNumber();
    const network = await provider.getNetwork();
    const gasPrice = await provider.getGasPrice();

    return {
        chain: 'ethereum-sepolia',
        blockHeight,
        network: network.name,
        status: 'healthy',
        gasPrice: ethers.utils.formatUnits(gasPrice, 'gwei'),
        lastBlockTime: new Date().toISOString()
    };
}

Test it:

npx tsx src/index.ts
> get_chain_info

Response:

{
    "chain": "ethereum-sepolia",
    "blockHeight": 9215400,
    "status": "healthy",
    "gasPrice": "12.5 gwei"
}

One down. Seven to go.

The Pattern Emerges

Each EVM chain (Polygon, BNB, Arbitrum, Avalanche) follows the same pattern:

Copy the Ethereum server. Change 3 things:

  1. RPC endpoint
  2. Chain ID
  3. Network name

Four hours later, I have 5 EVM chains running:

# Terminal windows stacked like a Christmas tree
ethereum-sepolia: ✅ Block 9,215,400
polygon-mainnet:  ✅ Block 76,500,000
arbitrum-mainnet: ✅ Block 379,100,000
avalanche-cchain: ✅ Block 68,800,000
bnb-chain:        ✅ Block 61,300,000

All responding to the same commands. All returning data in the same format. All feeling like one unified system.

The insight: EVM chains are easy. The hard part is everything else.

Phase 2: Bitcoin (Hours 8-16)

The UTXO Problem

Bitcoin isn’t account-based. It’s UTXO-based (Unspent Transaction Output).

You don’t have “an address with a balance.” You have “a collection of unspent outputs from previous transactions that your private key can spend.”

This breaks everything.

On EVM chains:

const balance = await provider.getBalance(address);
// Returns: "1.5 ETH"

On Bitcoin:

const utxos = await getUTXOs(address);
const balance = utxos.reduce((sum, utxo) => sum + utxo.value, 0);
// Returns: "1.5 BTC" (but it's 47 different UTXOs)

To send a transaction on Bitcoin, you need to:

  1. Select which UTXOs to spend
  2. Calculate the exact fee
  3. Create change outputs (send the leftover back to yourself)
  4. Sign each input separately
  5. Broadcast the whole thing

On Ethereum, you just say “send 1 ETH.” Bitcoin makes you do math.

The Bitcoin Breakthrough

I spent 6 hours building UTXO management. The logic is gnarly:

function selectUTXOs(utxos: UTXO[], targetAmount: number, feeRate: number) {
    // Sort by value (largest first)
    const sorted = utxos.sort((a, b) => b.value - a.value);

    let selected = [];
    let total = 0;
    let fee = 0;

    for (const utxo of sorted) {
        selected.push(utxo);
        total += utxo.value;

        // Estimate fee (1 input = ~150 bytes)
        fee = (selected.length * 150) * feeRate;

        // Do we have enough?
        if (total >= targetAmount + fee) {
            return { selected, fee, change: total - targetAmount - fee };
        }
    }

    throw new Error('Insufficient funds');
}

Test it:

> bitcoin_get_balance bc1qtest...
{
  "confirmed": "1.5 BTC",
  "unconfirmed": "0.0 BTC",
  "utxos": 47
}

> bitcoin_send_transaction ...
{
  "txid": "abc123...",
  "fee": "0.00012 BTC",
  "size": "372 bytes"
}

It works. Bitcoin joins the ecosystem.

ethereum-sepolia: ✅
polygon-mainnet:  ✅
arbitrum-mainnet: ✅
avalanche-cchain: ✅
bnb-chain:        ✅
bitcoin-testnet:  ✅

Six down. Two to go.

Phase 3: Cosmos (Hours 16-24)

The IBC Rabbit Hole

Cosmos is built for cross-chain communication. It has IBC (Inter-Blockchain Communication) natively built in. This should be easy.

It is not easy.

Cosmos uses:

And then there’s staking.

97% of ATOM tokens are staked. Everyone on Cosmos stakes. It’s not optional—it’s the culture.

I need to build:

async function delegateTokens(
    delegator: string,
    validator: string,
    amount: string
) {
    const msg = {
        typeUrl: "/cosmos.staking.v1beta1.MsgDelegate",
        value: {
            delegatorAddress: delegator,
            validatorAddress: validator,
            amount: {
                denom: "uatom",
                amount: amount
            }
        }
    };

    return await client.signAndBroadcast(delegator, [msg], fee);
}

The breakthrough: Cosmos SDK has good TypeScript libraries (@cosmjs/stargate). Once you learn the patterns, it’s actually elegant.

Test it:

> cosmos_get_chain_info
{
  "chain": "cosmos-hub",
  "blockHeight": 27500000,
  "stakingRatio": "97%",
  "bondedTokens": "285M ATOM"
}

> cosmos_delegate_tokens ...
{
  "txHash": "xyz789...",
  "validator": "cosmosvaloper1...",
  "amount": "100 ATOM"
}

Seven chains operational.

Phase 4: Solana (Hours 24-36)

The Speed Demon

Solana is fast. 400ms block times. Parallel transaction processing. 3,000+ TPS in production.

It’s also completely different from everything else.

No mempool. Transactions go directly to validators. Accounts everywhere. Everything is an account (programs, data, tokens). Rent. Accounts need SOL to exist (or they get garbage collected). Programs, not contracts. They’re called “programs” and written in Rust.

The learning curve is steep. But the tooling is surprisingly good (@solana/web3.js).

I build the core tools:

async function getBalance(address: string) {
    const pubKey = new PublicKey(address);
    const balance = await connection.getBalance(pubKey);
    return {
        address,
        balance: balance / LAMPORTS_PER_SOL,
        lamports: balance
    };
}

async function sendTransaction(
    from: Keypair,
    to: string,
    amount: number
) {
    const transaction = new Transaction().add(
        SystemProgram.transfer({
            fromPubkey: from.publicKey,
            toPubkey: new PublicKey(to),
            lamports: amount * LAMPORTS_PER_SOL
        })
    );

    return await sendAndConfirmTransaction(connection, transaction, [from]);
}

Test on Solana devnet:

> solana_get_chain_info
{
  "chain": "solana-devnet",
  "slot": 358000000,
  "tps": "~3000",
  "blockTime": "400ms"
}

All 8 chains online.

ethereum-sepolia: ✅ Block 9,215,400
polygon-mainnet:  ✅ Block 76,500,000
arbitrum-mainnet: ✅ Block 379,100,000
avalanche-cchain: ✅ Block 68,800,000
bnb-chain:        ✅ Block 61,300,000
bitcoin-testnet:  ✅ Block 4,661,802
cosmos-hub:       ✅ Block 27,500,000
solana-devnet:    ✅ Slot 358,000,000

The Integration Test

September 17, 2 PM

Time to see if this actually works as a unified system.

I open Claude Desktop and try a cross-chain workflow:

Me: "Check my balance on Ethereum, Polygon, and Bitcoin"

Claude: *calls three MCP servers in parallel*
- Ethereum: 0.5 ETH ($1,825)
- Polygon: 100 MATIC ($72)
- Bitcoin: 0.01 BTC ($670)

Total portfolio: $2,567

Me: "Which chain has the cheapest transaction fees right now?"

Claude:
- Ethereum: $12.50 (50 gwei)
- Polygon: $0.02 (30 gwei)
- Bitcoin: $1.20 (10 sat/vB)

Polygon is cheapest by far.

Me: "Send 10 MATIC to [address]"

Claude: *calls polygon server*
Transaction sent!
TxHash: 0xabc123...
Fee: $0.02

It works. Three different blockchains. One conversation.

The Cross-Chain Arbitrage Test

Now for the real test—the arbitrage opportunity that started this whole thing:

Me: "Check USDC price on Ethereum, Polygon, and BNB Chain"

Claude: *calls market data + blockchain servers*
- Ethereum: $1.002 (via Uniswap)
- Polygon: $0.998 (via QuickSwap)
- BNB Chain: $1.001 (via PancakeSwap)

There's a 0.4% spread between Polygon and Ethereum.

Me: "Calculate if arbitrage is profitable after fees"

Claude:
Buy on Polygon: $0.998 + $0.02 fee = $0.9982
Sell on Ethereum: $1.002 - $12.50 fee = ...

Actually, no. Ethereum gas kills this trade.
You'd need to trade $31,250+ to break even.

Me: "What about Polygon to BNB?"

Claude:
Buy on Polygon: $0.998 + $0.02 = $0.9982
Sell on BNB: $1.001 - $0.08 = $1.0002

Profit: $0.002 per USDC
On $10,000: $20 profit

Profitable! But barely.

The system works. More importantly, it works together. The arbitrage calculation needed:

All in one conversation. All feeling natural.

The Unexpected Benefits

Benefit 1: Pattern Recognition

Building 8 servers forced us to see patterns we’d missed before.

Every blockchain needs:

These became the MBPS v2.1 universal tools. The standard emerged from necessity.

Benefit 2: Error Handling

When one server goes down, the others keep working.

Me: "Check balances across all chains"

Claude:
- Ethereum: 0.5 ETH ✅
- Polygon: 100 MATIC ✅
- Arbitrum: 50 ARB ✅
- Avalanche: Error (RPC timeout) ❌
- BNB: 5 BNB ✅
- Bitcoin: 0.01 BTC ✅
- Cosmos: 1000 ATOM ✅
- Solana: 10 SOL ✅

7 of 8 chains responding.
Total value: $2,432 (excluding Avalanche)

Partial failures don’t break the whole system. Users get results from chains that work, with clear indicators for chains that don’t.

Benefit 3: Real Cross-Chain Development

The Bloomberg Terminal weekend rescue (Post #25) was only possible because this infrastructure existed.

We weren’t connecting “an Ethereum server.” We were connecting “a unified multi-chain interface.”

One integration gave us:

All at once.

The Operational Reality

What We Monitor

Each chain reports health metrics every 5 minutes:

interface NetworkHealth {
    chain: string;
    status: 'healthy' | 'degraded' | 'down';
    blockHeight: number;
    lastBlockTime: string;
    peerCount?: number;
    avgResponseTime: number;
}

Dashboard view:

Ethereum:  ✅ Healthy   (450ms avg)
Polygon:   ✅ Healthy   (180ms avg)
Arbitrum:  ✅ Healthy   (160ms avg)
Avalanche: ⚠️  Degraded (820ms avg - RPC slow)
BNB:       ✅ Healthy   (210ms avg)
Bitcoin:   ✅ Healthy   (320ms avg)
Cosmos:    ✅ Healthy   (340ms avg)
Solana:    ✅ Healthy   (120ms avg)

What Breaks (And How Often)

Week 1 Stats:

Failure breakdown:

Most reliable chains:

  1. Solana: 99.1% uptime (fastest RPC)
  2. Polygon: 98.7% uptime
  3. BNB: 97.2% uptime

Most problematic:

  1. Avalanche: 89.3% uptime (public RPC issues)
  2. Bitcoin: 92.1% uptime (testnet faucet problems)

The Cost

RPC Costs (Monthly):

Development Time:

Worth it? Absolutely. We can now test cross-chain functionality in minutes instead of days.

The Lessons

Lesson 1: Start Small, Expand Deliberately

We didn’t build 8 chains at once. We built 2 (Ethereum + Bitcoin), validated the patterns, then expanded.

The progression:

Each addition taught us something new. Each addition made the next one easier.

Lesson 2: Public RPC Endpoints Are a Gamble

Free public endpoints seem great until they:

We spent $100/month on reliable RPC providers. Best money we spent.

Lesson 3: The Ecosystem Is the Product

The individual servers are tools. The ecosystem is the product.

Users don’t think “I need to use the Ethereum server, then the Polygon server, then…”

They think: “I need to check my cross-chain portfolio.”

The ecosystem makes that natural.

The Payoff

What We Can Do Now

Cross-chain portfolio tracking:

Me: "What's my total crypto worth?"

Claude: *queries 8 chains in parallel*
Total value: $47,234
- Ethereum: $28,450
- Bitcoin: $12,100
- Polygon: $3,200
- Solana: $2,100
- Others: $1,384

Cross-chain arbitrage scanning:

Me: "Find arbitrage opportunities across all chains"

Claude: *scans DEXs on 5 EVM chains*
Found 3 opportunities:
1. USDT: 0.3% spread (Polygon → BNB)
2. WETH: 0.5% spread (Arbitrum → Ethereum)
3. MATIC: 0.4% spread (Ethereum → Polygon)

Cross-chain NFT operations:

Me: "Mint an NFT on Solana, then bridge it to Ethereum"

Claude:
Step 1: Minting on Solana...
Step 2: Waiting for confirmation...
Step 3: Initiating bridge...
Step 4: Waiting for Ethereum finality...
Done! NFT now exists on both chains.

One conversation. Multiple chains. Seamless experience.

The Future

What’s Next

Additional networks:

Enhanced features:

Infrastructure improvements:

The Vision (Expanded)

What if every blockchain development team had this?

No more context-switching between chains. No more separate tools for separate networks. No more “we only support Ethereum.”

Just: “We support blockchains.”

Plural.

Conclusion

September 25, 2025. The ecosystem is operational.

Eight blockchains. Four architectures. One unified interface.

We can now:

All through natural language. All in Claude Desktop. All feeling like one system.

The breakthrough: It’s not about building 8 servers. It’s about building one ecosystem that happens to span 8 blockchains.

The difference matters.

When we started, cross-chain meant “multiple separate systems awkwardly talking to each other.”

Now it means: “Ask Claude. It handles all the chains.”

That’s the future we’re building.

Prerequisites

Deep Dives

Technical Context