How to Evaluate Block Builder Partnerships

A block builder is a specialized entity in Ethereum's Proposer-Builder Separation (PBS) model that constructs execution payloads. They compete to create the most valuable block by including transactions and MEV (Maximal Extractable Value). As a validator or solo staker, your choice of builder directly impacts your rewards and the network's health. Evaluating a partnership requires analyzing performance, economic terms, transparency, and security.

Start by assessing the builder's performance and reliability. Key metrics include proposal success rate (the percentage of times their payload is successfully proposed), latency (time to deliver the payload after a request), and uptime. A builder with a 99%+ success rate and sub-second latency minimizes missed opportunities. Tools like mevboost.pics provide public dashboards for comparing builder performance across these metrics.

The economic proposal is central. Builders typically offer a fee, often as a percentage of the block's total priority fees and MEV, paid to the validator. Compare the fee structure—is it a flat percentage, a tiered model, or a minimum guaranteed payout? Be wary of offers that seem too good to be true, as they may indicate unsustainable practices or hidden risks. Analyze historical payout data to verify consistency.

Transparency and operational security are non-negotiable. A reputable builder should publicly disclose their relay partnerships, software client (e.g., MEV-Boost), and have a clear slashing policy. They should operate multiple, geographically distributed relays to ensure redundancy. Evaluate their commitment to censorship resistance—do they have a policy against OFAC compliance that could lead to transaction filtering?

Finally, consider the builder's technical integration and support. The process should be straightforward, using standard APIs and well-documented clients like Lighthouse or Teku. Good builders provide clear setup guides, real-time monitoring tools, and responsive support channels. Test the integration on a testnet like Goerli before committing mainnet funds. A strong partnership is built on clear communication and reliable infrastructure.

A block builder is a specialized entity in Ethereum's Proposer-Builder Separation (PBS) architecture. They are responsible for constructing the most profitable block possible by aggregating user transactions from the mempool and private order flow, including MEV opportunities. The builder's output is a complete, executable block header and body, which they submit via a relay to validators (proposers) for inclusion in the chain. Understanding this role is fundamental; you are evaluating the entity that directly determines transaction ordering and block composition.

You must be familiar with the key metrics that define builder performance. Primary evaluation criteria include proposal success rate (how often a builder's block is chosen by a proposer), block value (the total priority fees and MEV captured, often measured in ETH or USD), and censorship resistance (the percentage of blocks that include transactions from the public mempool). Secondary metrics involve latency and reliability, which impact a builder's ability to win auctions. Tools like mevboost.pics, Relayscan, and EigenPhi provide public dashboards for this data.

Economic alignment is critical. Builders generate revenue from priority fees (tips from users) and MEV extraction (e.g., arbitrage, liquidations). Their costs include relay fees and the block proposal payment (the bid) made to the winning validator. A builder's profitability and sustainability depend on its ability to consistently outbid competitors while covering costs. Evaluate their revenue sources, bid strategy, and whether they share MEV rewards with proposers or stakers through mechanisms like MEV smoothing or MEV burn.

Assess the builder's technical infrastructure and operational security. A reliable builder requires high-performance mempool monitoring, fast execution clients (e.g., Geth, Erigon), and sophisticated MEV strategy algorithms. Their integration with multiple trusted relays (like Flashbots, BloXroute, Agnostic) is essential for reaching a broad validator set. Review their historical performance during network stress events, such as high gas price spikes or significant MEV opportunities, to gauge resilience. Public incident reports or post-mortems are valuable indicators of operational maturity.

Finally, consider the builder's commitment to Ethereum's core values. Analyze their censorship resistance track record—do they include OFAC-sanctioned transactions? Review their participation in builder governance initiatives, such as the inclusion list, and their stance on MEV democratization. A partnership should align with your validator's principles regarding network health and decentralization. The builder's transparency, communication channels for validators, and adherence to the Builder Specification are practical aspects of a sustainable partnership.

A block builder is a specialized entity that constructs the most profitable block of transactions from the mempool. In the proposer-builder separation (PBS) model, validators (proposers) outsource this complex task. The builder's primary goal is to maximize MEV (Maximal Extractable Value) through transaction ordering and inclusion, sharing a portion of the profits with the proposer via a bid. Your evaluation must assess their ability to generate consistent, high-value blocks while maintaining network integrity.

Start by auditing the builder's technical infrastructure and reliability. Key metrics include proposal success rate (percentage of assigned slots where a valid block is delivered), latency (time to deliver a built block after receiving the payload), and uptime. Builders should publish these stats via a public dashboard or API. For example, a builder with a 99.9% success rate and sub-second latency is more reliable than one with frequent missed slots. Also, verify their geographic distribution of nodes to mitigate single-point-of-failure risks.

Next, analyze the builder's economic performance and fee structure. Examine their historical bid distribution—the average and median value of their winning bids over time. A builder that consistently places top bids indicates sophisticated MEV extraction. Understand their payment model: do they offer a flat percentage of MEV, a priority fee, or a hybrid model? Scrutinize for any hidden fees or conditions. Transparency in revenue reporting is non-negotiable; you should be able to independently verify the profits attributed to your validator.

Security and trust are paramount. Evaluate the builder's operator reputation and operational history. Have they been involved in any malicious activities like time-bandit attacks or transaction censorship? Review their software stack: do they use open-source, audited software like mev-boost-relay or a proprietary system? Proprietary systems require greater scrutiny. Ensure they have robust slashing protection and fault-tolerant systems to prevent accidental slashing of your validator due to builder errors.

Finally, consider the builder's commitment to ecosystem health. Do they participate in MEV smoothing or MEV burn initiatives that benefit the broader network? Some builders, like those following ePBS (Enshrined PBS) principles, may align better with long-term protocol goals. Assess their policy on transaction inclusion: do they practice fair ordering or censorship resistance? Your choice influences network decentralization and resilience. Establish clear communication channels and service-level agreements (SLAs) before committing to a partnership.

Evaluating a block builder requires moving beyond simple uptime metrics to analyze a multi-dimensional performance profile. The primary technical criteria are reliability, latency, and value delivery. Reliability is measured by the builder's success rate in having its blocks accepted by the proposer, avoiding missed slots due to network issues or invalid block construction. Latency is critical; builders must submit their final block header within the tight 4-second window of a slot. Use tools like mevboost.pics or Relayscan.io to track a builder's historical inclusion rate and average bid arrival time relative to the slot deadline.

To assess value delivery, analyze the builder's bid distribution and MEV capture efficiency. High-performing builders consistently submit competitive bids, indicating they are effectively extracting value from the block space through arbitrage, liquidations, and other strategies. Examine public dashboards for metrics like average bid value (in ETH) and the percentage of blocks where the builder was the top bidder. A builder that frequently wins with low or zero-value bids may be unreliable or operating at a loss, which is unsustainable. Cross-reference this with the builder's censorship resistance score, which measures the percentage of OFAC-compliant blocks they produce.

Technical due diligence should include an evaluation of the builder's infrastructure and software stack. Inquire about their geographic distribution of nodes to mitigate latency, redundancy systems for high availability, and their client software (e.g., mev-boost, Flashbots SUAVE). Review their public incident history or post-mortems for past outages. For a hands-on test, you can run a monitoring script that tracks a specific builder's performance over time, logging bid submissions, win rates, and any missed slots. This data-driven approach provides an objective basis for partnership decisions, ensuring alignment with your validator's goals for profitability and network health.

The primary metric for evaluating a block builder is its proposer payment share, the percentage of the block's total MEV and fees returned to the validator. While a higher share is attractive, it must be weighed against reliability and risk. A builder offering 99% but with frequent missed slots or downtime provides less value than a consistent builder offering 95%. Analyze the builder's historical performance on platforms like mevboost.pics to verify their claimed share and slot success rate over time.

Beyond the payment percentage, examine the source and sustainability of the builder's revenue. Builders that rely heavily on aggressive arbitrage or liquidation MEV may see volatile earnings, while those with diverse strategies—including CEX-DEX arbitrage, NFT marketplace aggregation, and long-tail token swaps—offer more stable payouts. Investigate if the builder participates in censorship-resistant order flow auctions (like SUAVE) or if their strategies could be impacted by regulatory changes.

Assess the builder's operational security and transparency. A trustworthy builder will have a public relayer endpoint, clear documentation on their website (e.g., Flashbots docs), and a track record of handling transactions securely. Look for signs of economic alignment: does the builder also run validators, creating a stake in the network's health? Do they contribute to public goods or protocol development? These factors indicate a partner invested in the ecosystem's long-term success, not just short-term extraction.

Finally, consider the technical integration and support. Evaluate the builder's API reliability, latency, and the ease of switching between multiple builders for redundancy. A good partner provides clear monitoring tools and alerting for missed slots. Diversifying across 2-3 reputable builders mitigates reliance on a single point of failure and allows you to compare performance in real-time, ensuring you maximize your rewards while maintaining network resilience.