---
title: "Validate a proposed Stacks block"
method: POST
path: "/v3/block_proposal"
tags: ["Mining"]
---

# Validate a proposed Stacks block

`POST /v3/block_proposal`

Used by stackers to validate a proposed Stacks block from a miner.
**This API endpoint requires a basic Authorization header.**

## Request body

- object
  - `block` string, required — Hex-encoded block data (must be valid SIP-003 serialized block, typically 200+ bytes)
  - `chain_id` integer, required — Chain ID for the block

## Response `202`

Block proposal has been accepted for processing.
The result will be returned via the event observer.

- BlockProposalResponse — unresolved $ref

## Other responses

- `400` — Bad Request
- `401` — Unauthorized. Invalid or missing authentication token.
- `429` — There is an ongoing proposal validation being processed, the new request cannot be accepted until the prior request has been processed.
- `500` — Internal Server Error

## Changes

- **2026-01-28** `30468ca2533f` — 2 breaking, 1 warning
  - the `block` request property's minLength was increased from `0` to `400`
  - added the pattern `^([0-9a-fA-F]{2})+$` to the request property `block`
  - the `chain_id` request property's min was set to `0.00`
- **2026-01-14** `f7f733b4a1fc` — 2 info
  - the `block` request property's minLength was decreased from `400` to `0`
  - removed the pattern `^([0-9a-fA-F]{2})+$` from the request property `block`
- **2026-01-14** `eb2153a4a3ad` — 2 breaking, 1 warning
  - the `block` request property's minLength was increased from `0` to `400`
  - added the pattern `^([0-9a-fA-F]{2})+$` to the request property `block`
  - the `chain_id` request property's min was set to `0.00`
- **2026-01-02** `96224b968a3e` — 2 info
  - the `block` request property's minLength was decreased from `400` to `0`
  - removed the pattern `^([0-9a-fA-F]{2})+$` from the request property `block`
- **2025-12-18** `97e7080a8130` — 2 breaking, 1 warning
  - the `block` request property's minLength was increased from `0` to `400`
  - added the pattern `^([0-9a-fA-F]{2})+$` to the request property `block`
  - the `chain_id` request property's min was set to `0.00`

[Full history](https://skmtc.dev/stacks-network/apis/stacks-3-0-rpc-api/changes/v3/block_proposal/post.md)

---

[API](https://skmtc.dev/stacks-network/apis/stacks-3-0-rpc-api.md) · [All operations](https://skmtc.dev/stacks-network/apis/stacks-3-0-rpc-api/llms.txt) · [OpenAPI document](https://skmtc-service-production.skmtc.workers.dev/v1/apis/stacks-network/stacks-3-0-rpc-api/revisions/bfe6e0b30f62/schema)