grandpa_roundState | Mythos RPC Docs

Get the current GRANDPA finality round state on Mythos. Monitor consensus progress, validator voting participation, and finality health across the the gaming blockchain powering FIFA Rivals and NFL Rivals with World ID verification network.

Returns the state of the current GRANDPA finality round on Mythos when the endpoint exposes validator-round internals. GRANDPA (GHOST-based Recursive ANcestor Deriving Prefix Agreement) is the finality gadget used by many Substrate-based chains to provide deterministic finality, but some public endpoints do not surface grandpa_roundState and instead return a method-not-found style error.

Why Mythos? Build on the gaming blockchain powering FIFA Rivals and NFL Rivals with World ID verification with World ID proof-of-humanity, Polkadot security, Snowbridge cross-chain bridge, and 1M+ downloads per title.

When to Use This Method

grandpa_roundState is essential for game studios, player-driven economy builders, and teams requiring verified human-only gameplay:

Finality Monitoring -- Track whether GRANDPA rounds are progressing normally or stalling on Mythos, critical for AAA gaming (FIFA Rivals, NFL Rivals, Pudgy Party), player-owned economies, and bot-resistant matchmaking
Consensus Health Checks -- Detect finality delays by comparing prevote/precommit counts against the supermajority threshold weight
Validator Participation Analysis -- Monitor which validators are actively voting and whether the authority set has sufficient online weight
Authority Set Tracking -- Observe setId changes after validator set rotations to verify smooth authority transitions
Capability Detection -- Confirm whether the shared endpoint exposes GRANDPA round internals before you build monitoring around them

Code Examples

Bash

curl -X POST https://api-mythos-archive.n.dwellir.com/YOUR_API_KEY \
  -H "Content-Type: application/json" \
  -d '{
    "jsonrpc": "2.0",
    "method": "grandpa_roundState",
    "params": [],
    "id": 1
  }'

Common Use Cases

1. Finality Health Monitoring

Periodically check whether GRANDPA rounds are progressing and alert on stalls:

JavaScript

import { ApiPromise, WsProvider } from '@polkadot/api';

async function monitorFinality(api, intervalMs = 10000) {
  let lastRound = 0;
  let lastSetId = 0;
  let stallCount = 0;

  setInterval(async () => {
    const state = await api.rpc.grandpa.roundState();
    const best = state.best;
    const round = best.round.toNumber();
    const setId = state.setId.toNumber();
    const prevoteProgress = best.prevotes.currentWeight.toNumber();
    const precommitProgress = best.precommits.currentWeight.toNumber();
    const threshold = best.thresholdWeight.toNumber();

    if (setId !== lastSetId) {
      console.log(`Authority set changed: ${lastSetId} -> ${setId}`);
      lastSetId = setId;
    }

    if (round === lastRound) {
      stallCount++;
      if (stallCount >= 3) {
        console.warn(`GRANDPA round ${round} stalled for ${stallCount} checks`);
        console.warn(`  Prevotes: ${prevoteProgress}/${threshold}`);
        console.warn(`  Precommits: ${precommitProgress}/${threshold}`);
        console.warn(`  Missing voters: ${best.precommits.missing.length}`);
      }
    } else {
      stallCount = 0;
      console.log(`Round ${round} | prevotes=${prevoteProgress}/${threshold} precommits=${precommitProgress}/${threshold}`);
    }

    lastRound = round;
  }, intervalMs);
}

2. Validator Participation Report

Generate a report of which validators are consistently missing votes:

JavaScript

async function trackMissingVoters(api, samples = 20, delayMs = 6000) {
  const missingCounts = {};

  for (let i = 0; i < samples; i++) {
    const state = await api.rpc.grandpa.roundState();
    const missing = state.best.precommits.missing;

    missing.forEach((authority) => {
      const key = authority.toString();
      missingCounts[key] = (missingCounts[key] || 0) + 1;
    });

    await new Promise((resolve) => setTimeout(resolve, delayMs));
  }

  // Sort by most frequently missing
  const sorted = Object.entries(missingCounts)
    .sort(([, a], [, b]) => b - a);

  console.log('Validator participation report:');
  sorted.forEach(([authority, count]) => {
    const missRate = ((count / samples) * 100).toFixed(1);
    console.log(`  ${authority}: missed ${count}/${samples} (${missRate}%)`);
  });

  return sorted;
}

3. Supported-Fallback Check

If the endpoint does not expose GRANDPA round internals, fall back to finalized-head tracking:

JavaScript

async function getFinalitySignal(api) {
  try {
    return { supported: true, roundState: await api.rpc.grandpa.roundState() };
  } catch (error) {
    return {
      supported: false,
      finalizedHead: (await api.rpc.chain.getFinalizedHead()).toHex(),
      message: error.message
    };
  }
}

3. Finality Lag Detection

Compare the finalized head with the best block to measure finality lag:

JavaScript

async function getFinalityLag(api) {
  const [roundState, finalizedHash, bestHeader] = await Promise.all([
    api.rpc.grandpa.roundState(),
    api.rpc.chain.getFinalizedHead(),
    api.rpc.chain.getHeader()
  ]);

  const finalizedHeader = await api.rpc.chain.getHeader(finalizedHash);
  const bestNumber = bestHeader.number.toNumber();
  const finalizedNumber = finalizedHeader.number.toNumber();
  const lag = bestNumber - finalizedNumber;

  return {
    bestBlock: bestNumber,
    finalizedBlock: finalizedNumber,
    lagBlocks: lag,
    grandpaRound: roundState.best.round.toNumber(),
    setId: roundState.setId.toNumber(),
    prevoteReached: roundState.best.prevotes.currentWeight.toNumber() >= roundState.best.thresholdWeight.toNumber(),
    precommitReached: roundState.best.precommits.currentWeight.toNumber() >= roundState.best.thresholdWeight.toNumber()
  };
}

Understanding GRANDPA Rounds

GRANDPA achieves finality through a two-phase voting protocol:

Prevote Phase -- Each authority broadcasts a prevote for the highest block they consider best. Once prevotes reach the thresholdWeight (supermajority), the protocol derives the highest block that is an ancestor of all supermajority prevotes.
Precommit Phase -- Authorities that observe a supermajority of prevotes issue precommits for the block derived in the prevote phase. When precommits reach the threshold, that block and all its ancestors are finalized.
Authority Sets -- The setId increments each time the authority set changes (e.g., after a session rotation). A new authority set starts a new round sequence from round 1.

Concept	Description
totalWeight	Sum of all authority weights in the current set
thresholdWeight	`⌊totalWeight × 2/3⌋ + 1` -- minimum for supermajority
Healthy round	`prevotes.currentWeight >= thresholdWeight` AND `precommits.currentWeight >= thresholdWeight`
Stalled round	Neither prevotes nor precommits reach threshold for an extended period

Error Handling

Common errors and solutions:

Error Code	Description	Solution
-32603	Internal error	The node may not be running the GRANDPA protocol (e.g., light client or parachain collator) -- verify node type
-32601	Method not found	GRANDPA RPC is not enabled on this node -- check the node's `--rpc-methods` configuration
-32005	Rate limit exceeded	Reduce polling frequency or implement client-side rate limiting
Empty response	No round data	Node may still be syncing or the GRANDPA voter has not started -- wait for sync completion

chain_getFinalizedHead -- Get the hash of the latest finalized block
chain_subscribeFinalizedHeads -- Subscribe to new finalized block headers
grandpa_proveFinality -- Get a finality proof for a specific block number
beefy_getFinalizedHead -- Get the latest BEEFY finalized block (if BEEFY is enabled)
system_health -- Check overall node health including sync and peer status

grandpa_roundState - Mythos RPC Method

When to Use This Method

Code Examples

Common Use Cases

1. Finality Health Monitoring

2. Validator Participation Report

3. Supported-Fallback Check

3. Finality Lag Detection

Understanding GRANDPA Rounds

Error Handling

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