MEV-Boost Relay Data API Integration Guide

introduction

RELAY DATA API INTEGRATION

Introduction

A technical reference for building software that consumes data from the MEV-Boost Relay API.

The MEV-Boost Relay API is the primary public data interface for the proposer-builder separation (PBS) pipeline. While the core auction endpoints (getHeader, submitBlindedBlock) facilitate the real-time block-building market, a parallel set of data endpoints exposes historical and current state about proposer payloads, builder submissions, and validator registrations. This page provides a technical reference for developers building custom software—such as block explorers, analytics platforms, or compliance dashboards—that integrates directly with these relay data APIs.

Integrating with the data API requires careful handling of relay-specific rate limiting, pagination, and data schema variations. The canonical specification defines standard endpoints like /relay/v1/data/bidtraces/proposer_payload_delivered and /relay/v1/data/validator_registration, but relay operators may implement additional filtering or custom query parameters. A robust integration must account for eventual consistency in data delivery, as a relay may serve a payload over the auction API before it is indexed and available via the data API. Builders and searchers often cross-reference this data to audit builder performance, verify inclusion, and detect relay equivocation or unbundling events.

For analytics platforms, the data API is the source of truth for metrics such as builder market share, validator registration diversity, and block value distribution. A common integration pattern involves polling the proposer_payload_delivered endpoint to reconstruct the canonical chain of MEV-Boost blocks and joining this with execution layer data to calculate MEV rewards. Teams building monitoring or compliance tooling should be aware that relays operating OFAC-compliant filtering policies may return a subset of the full payload data, and cross-referencing multiple relays is necessary for a complete view of the network. Chainscore Labs can assist with integration architecture review, schema normalization across relay implementations, and building resilient data pipelines that handle relay downtime and API upgrades.

RELAY DATA API INTEGRATION

Quick Facts

Operational and technical facts for teams integrating with MEV-Boost relay data APIs for analytics, monitoring, or block explorer applications.

Area	What changes	Who is affected	Action
Data API Endpoints	Relays expose RESTful endpoints for proposer payloads, builder submissions, and validator registrations. Schema and availability vary by relay implementation.	Block explorers, analytics platforms, MEV watchdogs	Audit relay-specific OpenAPI specs for payload delivery, bid traces, and registration endpoints. Do not assume uniform schema across relays.
Rate Limiting	Relays enforce strict rate limits to protect auction integrity. Limits are often unpublished and can trigger temporary or permanent IP bans.	Data aggregators, high-frequency monitors	Implement exponential backoff and respect 429 response headers. Contact relay operators for documented limits before production scraping.
Data Latency	Payload and bid data availability is subject to relay internal processing delays. Data is not guaranteed to be available within the slot time.	Real-time dashboards, trading systems	Benchmark data freshness per relay. Do not use relay data APIs for sub-second decision-making without direct relay operator coordination.
Validator Registration Data	The `validator_registration` endpoint exposes public keys and fee recipients. This data links validators to chosen relays and MEV strategies.	Staking pools, compliance teams, researchers	Review privacy implications before indexing or publishing registration data. Validator-registration correlation can reveal operational patterns.
Bid Trace Endpoints	Some relays expose bid traces showing the full builder submission and selection lifecycle. This is critical for auditing builder behavior.	Builder reputation systems, protocol analysts	Verify bid trace completeness against landed block data. Missing traces may indicate relay-side filtering or data pipeline gaps.
Relay Software Diversity	Relay implementations (e.g., Flashbots, bloXroute, Ultrasound) have different API behaviors, error codes, and data retention policies.	Multi-relay integrators, cross-relay analytics	Build abstraction layers that normalize relay-specific quirks. Test against each relay's staging environment before production deployment.
Data Retention	Relays are not required to retain historical data. Payloads and bids may be pruned after a few days or weeks.	Historical analysis platforms, compliance auditors	Do not treat relay APIs as permanent archives. Mirror data to your own infrastructure if long-term retention is required.
API Stability	Relay data APIs are not governed by a formal specification process. Endpoints and schemas can change without notice.	All integrators	Pin integration tests to specific relay API versions. Monitor relay operator communication channels for deprecation notices.

technical-context

RELAY DATA API REFERENCE

API Architecture and Endpoint Map

A structural map of the MEV-Boost Relay Data API, detailing the endpoint categories, their operational dependencies, and the architectural constraints that govern data access for builders, validators, and analytics platforms.

The MEV-Boost Relay Data API is the primary interface for external observers to query the state of the proposer-builder separation (PBS) pipeline. It is logically partitioned into three distinct data domains: validator registrations, builder block submissions, and delivered payloads. Each domain exposes a set of RESTful endpoints that serve JSON payloads, providing a window into the relay's internal state machine. For developers building block explorers, MEV analytics dashboards, or validator monitoring tools, understanding this endpoint map is the first step to integrating with the Flashbots relay ecosystem and other compliant relays.

The validator registration endpoints expose the set of public keys and their associated fee recipients that have been registered with the relay. This data is critical for correlating proposer duties with expected MEV revenue. The builder submissions endpoints provide access to the ExecutionPayloadHeader objects submitted by builders during the auction, including the block_hash, value, and parent_hash. This allows integrators to reconstruct the competitive bidding landscape for any given slot. The delivered payloads endpoints return the full ExecutionPayload for blocks that were successfully proposed via the relay, enabling post-hoc analysis of MEV extraction, sandwich attacks, and builder profit margins. A key architectural constraint is that the relay only serves data for slots where it was the winning bidder; data for slots won by other relays or local execution clients is not available.

Operational integration requires careful handling of the relay's rate-limiting and data consistency model. Relays typically implement aggressive rate limits on the /relay/v1/data/bidtraces/proposer_payload_delivered endpoint to prevent resource exhaustion. Integrators should prefer polling the lighter /relay/v1/data/bidtraces/builder_blocks_received endpoint for near-real-time bid monitoring and only fetch full payloads on a confirmed delivery event. Furthermore, the data schema is defined by the open-source relay-specs repository, but relay operators may introduce minor extensions. Teams building production-grade monitoring systems must implement schema validation and graceful degradation to handle these variations. Chainscore Labs can assist with a formal review of your relay data pipeline, ensuring your integration is resilient to schema drift, rate-limit errors, and relay-specific quirks.

Who integrates with the relay data API and why

Integration Use Cases by Actor

Block Explorer Integration

Block explorers consume the relay data API to attribute blocks to specific builders and relays, enriching the canonical block view with MEV-Boost metadata. The primary endpoint is getPayloadDelivered, which provides the mapping between a slot number and the winning builder's payload.

Key integration steps:

Poll the /relay/v1/data/bidtraces/proposer_payload_delivered endpoint to fetch delivered payloads for each slot.
Correlate the returned block_hash with on-chain block data to display builder and relay attribution.
Handle edge cases where a slot was missed or a validator built a local block, resulting in no relay-delivered payload.
Implement backfill logic for historical slots to populate the explorer database.

Operational concerns: Rate limiting is the primary failure mode. Explorers must implement exponential backoff and respect Retry-After headers. Relay availability varies; explorers should query multiple relays to ensure complete coverage of the proposer set.

implementation-impact

RELAY API INTEGRATION

Implementation Considerations

Building a robust integration with MEV-Boost relay data APIs requires careful handling of rate limits, data consistency, and schema evolution. The following areas demand specific architectural attention.

Rate Limiting and Retry Logic

Relay operators enforce strict rate limits on data API endpoints to protect infrastructure. Integrations must implement exponential backoff with jitter, respect Retry-After headers, and cache responses aggressively. A builder block explorer that polls /relay/v1/data/bidtraces/proposer_payload_delivered every slot can quickly exhaust its quota. Design your ingestion pipeline to use websocket streams where available and fall back to polling only for initial state hydration.

EXPLORE

Data Schema Versioning and Compatibility

The relay data API schema is not formally versioned and fields can be added, deprecated, or change semantics between relay implementations. A field like block_value in a delivered payload endpoint may represent the bid value in one relay and the final block value in another. Build your ingestion layer with a schema registry that validates incoming payloads and flags unexpected fields for review rather than silently dropping them or crashing the pipeline.

Cross-Relay Data Consistency

No single relay sees the full MEV-Boost auction. A builder may win blocks on multiple relays, and a validator's getHeader request is broadcast to all connected relays. Reconstructing a canonical view of the builder market requires deduplicating payloads across relays using slot and block_hash as a composite key. Be aware that relay clock drift can cause slot boundary disagreements, leading to missed or duplicated records at epoch transitions.

Validator Registration and Proposer Duty Tracking

The /relay/v1/data/validator_registration endpoint returns the set of validators registered with a relay, but this is a point-in-time snapshot. A validator may register, deregister, or change fee recipients between slots. For accurate proposer duty analysis, you must correlate this data with beacon chain proposer schedule lookahead. Relying solely on relay registration data will misattribute missed slots to validators that were never scheduled to propose.

BidTrace Integrity and Builder Identification

The bid_trace object is the core data structure for builder attribution, but its fields are self-reported by builders. A malicious builder can spoof the builder_pubkey or submit traces with manipulated value fields. For analytics platforms, cross-reference bid traces with on-chain proposer_fee_recipient and block.coinbase transfers. Do not treat relay data API responses as cryptographically verified execution payloads without independent validation.

Latency Sensitivity for Real-Time Dashboards

Relay data APIs are eventually consistent. A delivered payload may not appear in the /proposer_payload_delivered endpoint for several slots after the block is proposed. For real-time monitoring dashboards, supplement relay API polling with direct EL/CL client subscriptions via the Beacon API block event stream. Use the relay API as a backfill and attribution layer, not as the primary source for slot-by-slot block proposal alerts.

RELAY API INTEGRATION POINTS

Integration Risk Matrix

Risk assessment for software systems that consume data from or submit payloads to MEV-Boost relay APIs. Each integration point carries distinct failure modes that affect data integrity, operational continuity, and competitive positioning.

Area	What changes	Who is affected	Action
Data API schema evolution	Relay operators may add, rename, or deprecate fields in the data API without formal versioning. Historical payload schemas can diverge across relay implementations.	Block explorers, analytics platforms, MEV dashboards	Implement schema validation on ingestion. Monitor relay-specific changelogs. Build abstraction layer that normalizes responses from multiple relay implementations.
Rate limiting and access policies	Relays enforce undocumented rate limits on data API endpoints. Limits may tighten during network congestion or after abuse incidents. Some relays require API keys for higher throughput.	Data aggregators, research teams, real-time monitoring systems	Implement exponential backoff and circuit breakers. Cache responses aggressively. Contact relay operators for documented limits. Design for degraded mode when a relay becomes unavailable.
Validator registration data accuracy	Validator registrations submitted via the relay API reflect intent but not on-chain state. Registrations may be stale, duplicated, or submitted by validators that are no longer active.	Staking pools, validator analytics tools, MEV reward calculators	Cross-reference registration data with beacon chain state. Treat registration data as a signal, not a source of truth. Flag validators with registrations older than two epochs.
Builder bid data completeness	Relays expose submitted bids but may omit bids that failed validation, arrived after the deadline, or were withdrawn. The visible bid set is not the full auction picture.	Builder performance monitors, auction fairness auditors, profit-switching logic	Do not assume the data API shows all bids. Correlate with landed block data on-chain. Missing bids may indicate relay-side filtering rather than builder inactivity.
Payload delivery latency	Data API endpoints may serve payloads with variable delay after slot finalization. Latency spikes during high-MEV periods or relay infrastructure issues.	Real-time dashboards, trading systems, automated response systems	Measure end-to-end latency per relay. Set alerts on delivery lag exceeding two slots. Use multiple relay data sources for redundancy in time-sensitive applications.
Relay-specific data semantics	Relays interpret fields like block value, gas used, and MEV reward differently. Some include priority fees in block value, others exclude them. Builder identification formats vary.	Cross-relay analytics, protocol revenue tracking, builder reputation systems	Document per-relay semantics. Normalize fields before aggregation. Publish assumptions in downstream data products. Verify against on-chain settlement data periodically.
Relay decommissioning or migration	Relays may shut down, merge, or change their API base URLs with limited notice. Historical data may become unavailable or move to new endpoints.	Long-term data archives, compliance reporting, historical research platforms	Maintain a registry of active relay endpoints. Archive raw API responses rather than only processed data. Build fallback data sources from block explorers or beacon chain data.

RELAY API INTEGRATION

Integration Rollout Checklist

A phased checklist for teams building custom software that consumes MEV-Boost relay data APIs. This covers the critical validation steps, error handling, and operational readiness checks required before deploying an integration that depends on relay data for block explorers, analytics platforms, or monitoring dashboards.

What to check: Fetch the /relay/v1/data/bidtraces/proposer_payload_delivered and /relay/v1/data/validator_registration endpoints from every relay you intend to consume. Diff the JSON response schemas, paying close attention to optional fields like block_number, num_tx, value, and builder_pubkey.

Why it matters: Relay implementations are not fully homogeneous. A field present and populated by Flashbots may be null or absent from a BloXroute or Ultrasound relay response. An integration that assumes a field is always present will crash or silently drop data.

Readiness signal: A schema compatibility matrix document showing field presence, type, and nullability for each target relay. Your parser must handle missing optional fields gracefully.

resource-links

CANONICAL SPECIFICATIONS AND IMPLEMENTATIONS

Source Resources

Use these upstream resources to validate endpoint schemas, fork-specific message types, relay behavior, and client compatibility before deploying a MEV-Boost Relay API integration.

Flashbots Relay API Specification

Start with the Flashbots relay specification when implementing Data API requests for proposer payloads, builder block submissions, or validator registrations. Confirm endpoint paths, query parameters, response ordering, pagination behavior, and bid-trace field types rather than deriving a schema from one relay’s output. Treat the published interface as a baseline, not proof that every public relay applies identical retention limits or rate limits. Capture unknown fields safely, use bounded request windows, and verify production behavior against each relay before depending on the API for accounting, compliance, or incident analysis.

EXPLORE

Ethereum Builder Specifications

Use the Ethereum builder specifications to track the consensus-facing types and Builder API semantics underlying relay data. Fork transitions can add or modify payload fields, commitments, request variants, and validation rules even when a Data API endpoint remains unchanged. Generate or version schemas by fork, preserve large numeric values without floating-point conversion, and reject structurally invalid records before indexing them. Teams should also compare the specification revision used by their consensus client, MEV-Boost deployment, and relay integrations to prevent silent incompatibility around an Ethereum network upgrade.

EXPLORE

MEV-Boost Client Implementation

Review the MEV-Boost source to understand how validator-side software calls relays, handles concurrent responses, validates bids, and falls back when relays fail. This is particularly useful when analytics need to distinguish relay observations from proposer behavior: a relay’s Data API does not expose every timeout, rejected response, or local block decision seen by the sidecar. Match your integration assumptions to the deployed MEV-Boost release, inspect release notes before upgrades, and reproduce request timing in a staging environment when investigating missing bids or payload-delivery discrepancies.

EXPLORE

MEV-Boost Relay Reference Implementation

Inspect the Flashbots relay implementation when specification text does not fully explain filtering, database queries, validation paths, or operational limits. The code can clarify how builder submissions and delivered payloads become Data API records, but it should not be treated as universal behavior across independently operated relays. Pin analysis to a specific commit or release, identify implementation-specific extensions, and test malformed parameters, empty results, duplicate observations, and high-volume queries. Operators should place caching and backoff in front of polling workloads so analytics traffic cannot interfere with auction-critical relay services.

EXPLORE

Ethereum Beacon API Specification

Use the Beacon API specification to reconcile relay records with canonical slots, blocks, validators, and chain reorganization status. A payload reported as delivered by a relay is not automatically proof that the corresponding block remained canonical. Join records using slot, block hash, parent hash, proposer public key, and execution payload identifiers where available, then update derived metrics after reorgs and finalization. Keep beacon-node queries separate from relay polling, and record the consensus client and API version used for reconciliation so historical analytics remain reproducible across schema and network upgrades.

EXPLORE

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RELAY API INTEGRATION FAQ

Frequently Asked Questions

Common technical questions for teams building custom software that interacts directly with MEV-Boost relay data APIs.

The standard relay data API exposes several key endpoints for fetching historical and current auction data:

/relay/v1/data/bidtraces/proposer_payload_delivered: Fetches payloads delivered to proposers. Query parameters typically include slot, block_hash, block_number, and cursor for pagination. The response schema includes the proposer_pubkey, block_hash, and the full execution_payload.
/relay/v1/data/bidtraces/builder_blocks_received: Fetches block submissions received from builders. This is critical for analyzing builder bidding behavior and market share. The schema includes builder_pubkey, block_hash, timestamp, and value.
/relay/v1/data/validator_registration: Fetches validator registrations for a given pubkey. This is essential for verifying which validators are connected to a specific relay.

Always check the specific relay's OpenAPI specification, as implementations may vary slightly from the reference spec. The canonical specification is maintained in the flashbots/relay-specs repository.

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MEV-Boost Relay API Integration

Introduction

Quick Facts

API Architecture and Endpoint Map

Integration Use Cases by Actor

Block Explorer Integration