indexer-blocks - SKILL.md Agent Skill

name: indexer-blocks description: >- Use when processing every block (or every Nth block) for time-series data, periodic snapshots, or block-level aggregations. indexer.onBlock API, where filter with block-number range and stride, and block handler context. metadata: managed-by: envio

Block Handlers

Process every block (or every Nth block) using indexer.onBlock. No contract address or config.yaml entry needed.

Handler

Branch by chain.id with a switch so the type system flags any unconfigured chain via the default: never exhaustiveness check:

import { indexer } from "envio";

indexer.onBlock(
  {
    name: "BlockTracker",
    where: ({ chain }) => {
      switch (chain.id) {
        case 1:
          return { block: { number: { _gte: 18000000, _every: 100 } } };
        case 8453:
          return { block: { number: { _every: 50 } } };
        default: {
          // Exhaustiveness check: TypeScript errors here if a new chain ID
          // is added to config.yaml but not handled above.
          const _exhaustive: never = chain.id;
          return false;
        }
      }
    },
  },
  async ({ block, context }) => {
    context.BlockSnapshot.set({
      id: `${block.number}`,
      blockNumber: BigInt(block.number),
    });
  }
);

Options

Option	Type	Required	Description
`name`	`string`	yes	Handler name for logging
`where`	`({ chain }) => boolean \| filter`	no	Predicate evaluated once per configured chain at registration. Return `false` to skip a chain, `true` / omit to match every block, or `{block: {number: {_gte?, _lte?, _every?}}}` to restrict range and stride. `_every` aligns relative to `_gte`, preserving `(blockNumber - _gte) % _every === 0`.

Other ecosystems

Fuel: same indexer.onBlock API; filter is keyed by block.height instead of block.number.
SVM: use indexer.onSlot; filter shape is {slot: {_gte?, _lte?, _every?}} and the handler arg is {slot: number, context} (no block wrapper).

Notes

indexer.onBlock self-registers — no config.yaml entry needed
No events or contract address required
The handler context has the same entity API as event handlers
If where returns false for every configured chain, a warning is logged at registration time
For per-event startBlock (not stride), use indexer.onEvent with where.block.number._gte (see indexer-filters). Event filters accept _gte only; _lte/_every are reserved for onBlock.

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