Intent Settlement Layers: Designing Solvers That Don’t Rug Your UX

A Practical Field Guide to Building and Buying Intent Settlement Layers

This guide is here to help you navigate the world of intent settlement layers. We’ll dive into how to set up auctions, limit solvers, and weave in shared sequencing and OFAs, so you can deliver speedy, fair, and MEV-safe execution while keeping trust trade-offs in check.

Structuring Auctions

When you're designing auctions, it's all about finding that sweet spot between efficiency and fairness. Consider different auction formats, whether it's first-price, second-price, or sealed bid, and figure out which one aligns best with your goals. Here are a few things to think about:

• Transparency: Make sure all participants know what's happening during the auction.
• Incentives: Create a structure that rewards honest bidding and discourages manipulation.
• Participation: Ensure the auction is accessible and easy for users to join.

Constraining Solvers

Constraining solvers can help keep the process fair and efficient. Here’s how to go about it:

• Limit Decision-Making Freedom: Set up parameters that guide solvers’ choices without stifling creativity.
• Incorporate Rules: Implement rules that prevent backdoor deals or other sketchy practices.
• Monitor Performance: Keep an eye on solver behavior to ensure they stick to the rules.

Integrating Shared Sequencing and OFAs

Integrating shared sequencing and Order-Filled Auctions (OFAs) is key to enhancing speed and fairness. Here’s what you need to know:

• Shared Sequencing: This allows for a collective approach, where multiple parties can contribute to the order sequence. It can help level the playing field and reduce the chances of frontrunning.
• OFA Implementation: Use OFAs to prioritize certain types of transactions, ensuring that users get what they need without delays.

Conclusion

Building and buying intent settlement layers doesn’t have to be a daunting task. By structuring your auctions smartly, constraining solvers effectively, and integrating shared sequencing with OFAs, you can create an environment that provides users with faster, fairer, and more secure execution. Keep these tips in mind, and you’re on your way to creating a robust system that meets everyone’s needs!

If you’re checking out CoW-style batch auctions, UniswapX RFQ/Dutch auctions, or shared sequencers like Astria (even looking into SUAVE-style order flow), this post has got you covered. Here, you’ll find solid design patterns, APIs, SLAs, and governance controls to help you build an intent stack that scales smoothly without messing up your product’s user experience.

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TL;DR

• Intents really help shift the heavy lifting away from users to a marketplace of “solvers” who are all vying to hit their goals based on the rules you set. The success of this approach isn’t just about price; it hinges on how well you design the auction, ensure fairness, and hold solvers accountable. You can read more about it here.
• CoW Protocol takes it up a notch with its fair combinatorial batch auctions and bonding/slashing mechanisms, setting a solid example for MEV-resilient price discovery and making sure solvers are held accountable at scale. For the nitty-gritty details, check out their documentation here.
• UniswapX's RFQ v2 and Dutch auctions bring in a cosigner and hard quotes to cut down on “quote fade.” This way, users won’t end up with the worst price within their quoted range--a clever tactic that can be applied to any intent layer. Discover how this works here.
• Shared sequencers, like the Astria mainnet alpha launching on October 28, 2024, play a crucial role in enabling cross-rollup atomicity and keeping censorship at bay. This is super important for completing multi-chain intents without centralizing order flow. Get the full scoop here.
• Order Flow Auctions (OFAs), such as Flashbots MEV-Share and MEV Blocker, are picking up steam in the market. They can be integrated with intent layers for quicker inclusion and to provide user rebates. You can dive deeper into this topic here.
• Keep an eye on emerging standards like ERC-7521, which introduces generalized intents for smart contract wallets, and EIP-7702, aimed at enabling EOAs to delegate to code (it's proposed for Pectra). These will pave the way for safer and more universal intent execution. Learn more here.

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What decision‑makers actually need from an intent layer

For both enterprise and consumer products, the right intent abstraction leads to:

• You can count on reliable fills over 99% at your target price--no more "best effort" nonsense.
• Expect predictable inclusion latencies (P50/P90) along with clear failover options when quotes fade away.
• We’ve got MEV-aware routing in place that makes sure any value goes back to you or your app, not some third-party builders.
• We're all about accountability: think bonding/slashing, KYC when necessary, and straightforward dispute rules.
• Enjoy multi-domain options: settle on your favorite L1/L2 today, and look forward to shared sequencers or cross-domain solutions tomorrow.

In the rest of this post, we'll connect those UX goals to some real strategies you can start using right away.

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Primer: intent settlement layers (ISLs) in practice

An ISL is like the backbone that takes user-signed "what I want" requests and converts them into on-chain state changes, all while keeping things safe and competitive. When it comes to designing one, here are the choices you need to make:

• Expression Format: This is all about how intents are signed, how constraints are laid out, and how the gas or payment system operates.
• Counterparty Discovery: Here, we're looking at who gets to see intents and at what time--are they public, private, or permissioned?
• Solving and Auctions: This section dives into how competition unfolds and the ways we ensure fairness in the process.
• Settlement: Finally, this covers how constraints are enforced on-chain and who takes on the risk of MEV (Miner Extractable Value) and gas costs.

Anoma lays out the stack as generalized intents → discovery → solving → settlement. This perspective is handy not just for its own chain but across the board. You can check it out more at anoma.net.

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Auction mechanics that won’t rug your users

1. Fair Batch Auctions with EBBO/UCP Guardrails

• Pattern: The CoW Protocol brings together intents, kicks off a solver competition, and picks the option that gives users the most benefits while keeping everything fair. It sticks to Uniform Clearing Prices and ensures an "Ethereum Best Bid/Offer" floor, so users can't end up with worse deals than what on-chain AMMs offer. (docs.cow.fi)
• Why it matters: UCP helps cut down on ordering games, while EBBO makes sure there's a fair starting point. Plus, the way batch combinatorics work lets solvers take advantage of the “coincidence of wants” without having to deal with liquidity provider fees. (docs.cow.fi)

RFQ v2 + Cosigner to Stop “Range-Rugging”

• Pattern: UniswapX’s RFQ v2 does a cool thing by separating indicative quotes from hard quotes. Once you sign, the quoters step in with hard quotes really quickly. There’s a cosigner (right now it’s Uniswap Labs in their interface) that makes sure the auctioneer doesn't snag the worst price within your signed range. If exclusivity goes south or starts to fade, it falls back to the Dutch auction model. For more details, check out the docs.uniswap.org.
• Why it matters: This setup allows for almost instant fills with fill rates close to 100% on the mainnet RFQ, so you won’t face those pesky “got the bottom of your slippage range” scenarios. You can dive deeper into this at docs.uniswap.org.

3) Dutch Auctions for Fast Chains

• Pattern: Over on Arbitrum, where blocks pop up every 0.25 seconds, UniswapX is shaking things up with direct Dutch auctions that skip the RFQ. Thanks to the quick block times, price discovery happens in a flash, making exclusivity a non-issue. You can dig into more details here.

1. Meta-aggregation without batching

• Pattern: UniswapX is stepping up as a meta-aggregator--every single trade is done on its own and comes with built-in MEV protection. Their fillers tap into both private and public liquidity, and they give back MEV as price improvements. If batching isn’t your thing, you can still replicate this execution race while ensuring solid protections. (x.uniswap.org)

Decision takeaway: If your users really care about strict fairness guarantees and sandwich immunity, go with batch auctions using EBBO/UCP. But, if speed and single-order latency are your main concerns, then the RFQ v2 combined with a Dutch auction and a cosigner is a solid choice.

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Solvers: make them compete--and make them accountable

You're putting your faith in solvers by letting them handle execution. Make sure they have a fair shot at winning, but also make losing a tough experience.

• Bonding and Slashing. CoW needs solvers to bond through pools, which used to be $500k in stables and 1.5M COW tokens. But here’s some good news: there's a new, easier path now that only needs $50k and 500k COW, plus some growth targets to hit. If someone misbehaves--think surplus shifts, overbidding, pennying, or omitting hooks--they can face slashing through a DAO process. And yes, these slashes are real and have actually happened! (docs.cow.fi)
• Shadow Competitions. We let new solvers test their skills against the production order flow before they get to handle any funds. It’s a great way to encourage measurable wins, too. (docs.cow.fi)
• Private Order Submission. We require MEV-safe relays and OFAs for settlement transactions. This keeps exposure low and allows us to offer rebates to users or integrators when it makes sense. (docs.cow.fi)
• Transparency. We’re all about being open here! We publish competition rules, unfair-bid filters, and the consequences of breaking the rules. The Local Token Conservation rules and clear penalties help keep “free option” behavior in check. (docs.cow.fi)

Procurement Checklist

• Bond Size
  Make sure you check the bond size required.
• Slashing Precedents
  Review any past slashing incidents to understand the risks involved.
• Audit Coverage
  Ensure that there’s adequate audit coverage in place.
• KYC
  Verify the Know Your Customer (KYC) processes are up to scratch.
• Private RPCs Used
  Look into the private Remote Procedure Calls (RPCs) that are being utilized.
• Quote Fade Rate
  Be aware of the quote fade rate to track any discrepancies.
• Solver’s Internal Risk Limits
  Check the internal risk limits set for the solver.
• Offtime Procedures
  Don’t forget to go over the offtime procedures.

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Shared sequencing and OFAs: faster inclusion, better UX

• Shared Sequencers for Multi-Rollup Intents
  Astria kicked off its mainnet alpha on October 25, 2024, introducing a decentralized shared sequencing layer. This means you get speedy pre-confirmations, solid censorship resistance, and atomic cross-rollup inclusion guarantees. If you're working on a product that needs cross-rollup intents--like a swap on L2 A that relies on a transfer from L2 B--using shared sequencing can really cut down on the “stuck leg” risk. Plus, it keeps everything from getting bogged down on a single chain. Check it out here: (astria.org)
• Order Flow Auctions (OFA) as a complement
  Flashbots MEV-Share introduces an open OFA, making it easier for wallets and dapps to share backrun value. Plus, CoW's MEV Blocker RPC speeds up inclusion and offers rebates through various endpoints tailored for different privacy and rebate preferences. You can seamlessly integrate your ISL's settlement transactions with an OFA right off the bat and pass those rebates on to your users or include them in your product’s fee structure. For more details, check out the Flashbots docs.
• Why now
  Flashbots’ 2024 State of Wallets report highlights that OFAs--like CoWSwap's batch executions, UniswapX's RFQ/Dutch auctions, and MEV-Blocker auction executions--are really picking up steam. It turns out users are all about that faster and safer experience when it comes to transactions. Check it out here: (writings.flashbots.net)

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Standards to future‑proof your stack

• ERC‑7521 (draft): This is all about creating generalized intents for smart contract wallets that have a single entry point. It routes to various intent standards so solvers can easily put things together. If you’re working on your own intent format, it’s a good idea to align with the 7521 to keep your users from getting stuck. Check it out here: (eips.ethereum.org)
• EIP‑7702 (Pectra scope): This is pretty cool--it allows EOAs (Externally Owned Accounts) to “delegate” actions to contract code using a new transaction type. It brings in a smoother batching and sponsorship experience for EOAs, but without adding new opcodes. Just keep in mind there are some important security and phishing concerns to consider. If you accept EOAs, make sure to track this for wallet support and user education. More info here: (eips.ethereum.org)

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A reference architecture we deploy for clients

1. Intent Expression and Signing

• Make sure to use an ERC‑7521‑compatible schema for smooth interoperability. It should cover: (a) price bounds, (b) time‑in‑force, (c) hook permissions, (d) MEV policy (like “private only”), and (e) a payout token for gas/fees. Check out more details on this at (eips.ethereum.org).

Example (simplified):

{
  "version": "1.0",
  "sender": "0xUser",
  "chainId": 1,
  "constraints": {
    "want": [{"token":"ETH","amount":"1.0"}],
    "give": [{"token":"USDC","amount":"<=2000"}],
    "minFill": "0.99",
    "ebbo": true,
    "deadline": 1732752000,
    "hooks": {"pre": [], "post": ["rebate", "notify"]},
    "mevPolicy": "private-only"
  },
  "signature": "0x..."
}

2) Discovery and Privacy

• Default: When you submit your intent, it goes straight to your intent gateway privately. You can choose to opt-in for gossip to the solver allowlist. We’ll only publish minimal fields to keep things safe and avoid any exploitation, kind of like what MEV-Share does with its selective disclosure. Check it out here: (docs.flashbots.net)

3) Auction Policy

• When it comes to multi-order flow and fairness, a batch auction using EBBO/UCP filters is the way to go. But if you’re all about that single-order low-latency life, then check out the RFQ v2 design with a cosigner and hard quotes; plus, there's a Dutch fallback on fade. For more details, head over to docs.cow.fi.

4) Solver Integration

• Get started through shadow competition; to move to production, you’ll need bonding and private submission. It’s crucial to stick to the competition rules and make sure to use MEV-safe builders along with OFA endpoints. Also, keep in mind that there will be programmatic penalties for any fading, illegal surplus shifts, or missing hooks. Check out more details in the docs.cow.fi.

5) Settlement and Inclusion

• To keep things smooth and efficient, make sure to route your winning solution through the MEV Blocker or your OFA partners. This helps reduce latency and ensures leak-free inclusion. If you have cross-rollup dependencies, consider integrating a shared sequencer like Astria for atomic inclusion guarantees or speedy pre-confirmations. Check out the details here.

6) Governance and Risk

• We’re looking at slashing either by DAO or board control, along with a clear and open incident response plan (you can check out the CoW slashing events for reference). Plus, we'll have independent monitoring and on-chain telemetry to track price improvements compared to EBBO. (forum.cow.fi)

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Two concrete patterns you can adopt this quarter

Pattern A: “Fair‑price batching” for larger trades

• Who: Think OTC-ish consumer apps, treasuries, and aggregators.
• How: We’re looking at a CoW-style batch auction, complete with EBBO guardrail and UCP. It uses solver bonding plus slashing, and for the private settlement, we’ve got the MEV Blocker in play. Plus, don’t forget the weekly scorecards where we publish stats like median price improvement, P90 fill latency, fade rate, and slashing incidents. Check it out here!
• Why: It gives users maximum assurance that things won’t be worse than AMM, along with solid MEV shielding. This is especially appealing for those who value trust.

Pattern B: “RFQ v2 + Dutch fallback” for latency-sensitive retail

• Who: Think mobile wallets and retail dapp frontends.
• How: We’ll use a cosigner to lock in the best executable price within the user's signed range. We'll demand hard quotes after signing, and if things start to fade, we’ll automatically switch to a Dutch auction. On fast L2s, we can even skip the RFQ altogether and go straight to the Dutch method with priority gas auctions. Check it out here: docs.uniswap.org
• Why: This setup gives you nearly instant fills and protects against quote gaming. Plus, the user experience is super smooth--it’s literally “tap and done” with MEV protection and no worries about failed transaction costs.

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Cross‑rollup intents: design for atomicity now

If your roadmap says “swap on Rollup A, deliver on Rollup B,” it’s time to get ahead and think about how you’ll sequence everything:

• Shared Sequencer Integration (Astria): This lets you use one temporal domain across different rollups, which means you can have atomic (or pretty close with some pre-confirmations) inclusion. It's a game changer for user experience compared to those multi-hop relays that depend on probabilistic finality. The Astria mainnet alpha has been up and running since October 2024, built for censorship resistance and speedy confirmations. Check it out at astria.org!
• Backstop Path: If shared sequencing isn't available for all the domains you're targeting, you can set up fallback options right in your intent. For example, you might say, “settle on A only” or “refund.” Just make sure to factor that risk into your auction parameters.

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SLAs, SLOs, and the scorecard you should demand

• Fill SLOs
  • For P50 inclusion, keep it under 2 blocks; for P90, aim for less than 6 on mainnet, or set chain-specific targets on those L2s.
  • Make sure the RFQ hard-quote fill rate hits at least 99%, and Dutch fallback success should be over 99.5% within a TTF of 30 seconds on speedy L2s. (docs.uniswap.org)
• Price SLOs
  • Enforce an EBBO floor 100% of the time during batch auctions; also, keep track of median price improvements compared to on-chain AMMs. (docs.cow.fi)
• Integrity SLOs
  • No unfair batched bids should be selected at all; ensure zero illegal surplus shifts. If violations happen, there should be slashing within 7 days, and make sure to post incident reports afterward (yes, this has precedent). (docs.cow.fi)
• Inclusion and rebates
  • Make sure that at least X% of settlement transactions go through OFA/private relays with observed rebates returned; don’t forget to share monthly rebate statistics. (docs.flashbots.net)

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Implementation notes your engineering team will thank you for

• Don’t try to recreate signatures from scratch. If you can, stick to the ERC‑7521 patterns for your intent signing. This will lighten the load on wallets later and make it simpler for third-party solvers to jump in. (eips.ethereum.org)
• Test your solvers in a sandbox. Run shadow comparisons against real production order flows; make sure you have reproducible simulation pipelines; set risk budgets for each solver; and limit order types during their probation period. (docs.cow.fi)
• Make privacy the default setting. Bring in a MEV‑Share-style selective disclosure system; let everyone know which fields are visible during different phases (like pre- vs post-signature). (docs.flashbots.net)
• If you’re the auctioneer, consider adding a cosigner. This completely eliminates the risk of the auctioneer picking the worst price in the range. (docs.uniswap.org)
• Clearly publish your competition rules--and stick to them. Make sure that any illegal surplus shift detection and overbidding penalties are coded into your system and governed properly. (docs.cow.fi)
• Think carefully about your settlement lane choices. On the mainnet, RFQ v2 with hard quotes works really well; on speedy L2s, Dutch auctions naturally compete with PGAs; also, consider routing your settlement through private builders or OFA endpoints. (docs.uniswap.org)
• Get ready for Pectra/7702. If users stick with EOAs, EIP‑7702 might make the user experience smoother with features like batching and sponsorship. Just keep an eye out for phishing risks and limit delegations to audited, immutable code paths. (ethereum.org)

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Brief, in‑depth examples

Example 1: Treasury Rebalancing, Large Tickets

• Constraints: “Buy 1,200 ETH with USDC at or better than EBBO; get it done in 5 minutes; keep it private with MEV; and let’s add some pre/post hooks for reporting.”
• Execution: We’ll go with a batch auction that uses EBBO/UCP. The solvers will tap into private MM inventory and on-chain liquidity, then submit everything through a private RPC (MEV Blocker) to keep things secure and minimize any data leakage. After that, we’ll publish the post-trade surplus compared to the AMM baseline. You can check out more details here.

Example 2: Retail Swap on Mainnet, Instant Feel

• Constraints: “Swap 2 ETH for USDC; accept outputs within a signed range.”
• Execution: Using RFQ v2 with a cosigner, the user signs off on the range. Hard quotes come in right after the signature, and the winning bid gets filled almost immediately. If it starts to fade, the order automatically jumps into a Dutch auction and settles without needing any permissions--plus, there’s no gas wasted on failed transactions. Check out more details in the docs.

Example 3: Cross-rollup “pay on A, deliver on B”

• Constraints: You’ll need to “Pay stablecoin on L2-A; receive NFT on L2-B; atomic or refund.”
• Execution: A shared sequencer takes care of coordinating the inclusion on both A and B. The solver stitches together the bridge and DEX legs as necessary. Users can expect a speedy pre-confirmation and final settlement once the DA wraps up. Plus, if anything goes wrong with the cross-domain leg, fallback refunds are in place. (astria.org)

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Emerging best practices (2025)

• Cosigned auctions: Take on a neutral cosigner role, even if you’re not running a UniswapX-style RFQ. It’s the easiest way to keep auctioneers in check. (docs.uniswap.org)
• Solver bonding tiers: Check out CoW’s streamlined bonding approach to boost competition while still keeping slashing in play. Make sure to require private submissions until the full bond is met. (forum.cow.fi)
• OFA-first routing: Go for default settlements using MEV Blocker/MEV-Share to cut down on latency and give some backrun value back to users. Don’t forget to tweak builder bids for any per-block fees from these RPCs. (docs.cow.fi)
• Shared sequencing pilots: If you’re working with multiple L2s, consider running a pilot with Astria. It’ll help you gauge inclusion latency and atomicity perks before you fully integrate these into your core processes. (astria.org)
• Standards alignment: Try to align your intent schema with ERC-7521 and keep an eye on the Pectra and 7702 wallet roadmaps for a smoother onboarding experience for EOAs. (eips.ethereum.org)

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The 7Block Labs checklist for an ISL that won’t rug UX

• Expression: We've got an ERC‑7521‑aligned schema here, plus an explicit EBBO/UCP or cosigner requirement, and don’t forget about the MEV policy field. Check it out here.
• Discovery: The default is private, but you can choose to disclose selectively. Oh, and make sure you audit your gossip! More info here.
• Auction: Users can decide between a pick batch or RFQ/Dutch based on their needs. Don’t forget to publish your rules and simulate things before you go live. Get the scoop here.
• Solvers: We're talking bonding and slashing with a solid historical context; there's also shadow comp, private settlements, and KYC if it’s necessary. Info available here.
• Settlement: We've integrated OFA for rebates and inclusion, plus there's a shared sequencer for atomic cross‑rollup legs. Dive deeper here.
• Governance: We've got an incident response runbook set up, a 7-day slashing window, and a quarterly public scorecard to keep things transparent. Find more details here.

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Bottom line

If you’re stuck deciding whether to build or buy, kick things off with RFQ v2 + a cosigner (single-order UX) or consider fair batch auctions using EBBO/UCP (portfolio/OTC). Then, you can add in OFA/private settlements. To keep your solvers on the straight and narrow, use bonding and slashing strategies. It’s also a good idea to pilot shared sequencing for your cross-rollup roadmap and make sure you’re in sync with ERC-7521 while keeping an eye on Pectra/7702. Your users are definitely going to notice the improvements in fills, latency, and trust--without you needing to downplay MEV or auction fairness.

7Block Labs is here to help teams get their systems up and running from start to finish. We cover everything from schema design and solver onboarding to auction rules, OFA routing, shared sequencing pilots, and the governance framework that ensures everything stays on the level.

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