balq — BAL query

Local, verified history of any contract's storage — on a full node, no archive node, no indexer schema. Built on EIP-7928 Block-Level Access Lists (Glamsterdam).

balq index 0x3582… --rpc http://localhost:8545 --layout Playground.json
  # watches it, walks older blocks back to the deploy, then follows — every block verified
  ✓ 0x3582…53ce  created at 114562 — history complete (2456 blocks, 131 records)
  117022  ▲ 6 record(s)   counter 19 → 20, totals.index …, items[4] 0 → …, [0xc0e2…8cd7] 60428 → 66428

balq get 0x3582… --layout Playground.json --field "balances[0x61Cc…]" --block 114591
→ balances[0x61Cc…] = 37585   (slot 0xc0e2…, set @ 114590, bal)

const view = archive.view(proxy, layout).at(114591);   // balq
view.balances[addr]   // 37585n  — reads like the contract, at any block

Why this could not exist before Glamsterdam

Before EIP-7928, "which storage slots changed in this block" lived only inside the node while it executed the block. To get it you either replayed blocks with a debug tracer (expensive, client-specific, unverifiable), trusted the contract's events (only what the author chose to log), or ran an archive node and asked slot by slot (15 TB, and you must already know which slots to ask for).

EIP-7928 puts the complete list of changed slots and their post-values into the block, and its hash into the header, under consensus. That turns "what changed" from a node's opinion into a fact of the block — complete by rule, verifiable with one keccak. balq is the tool that accumulates that fact, verifies it, and answers by variable name.

Three promises

1. Completeness. If a slot is not in the BAL, it did not change. Not "probably": a block with an incomplete BAL is invalid.
2. Verifiability. Every stored value is checked — the BAL against the header's hash, headers against each other by parent_hash, and the rare proven value by Merkle proof against state_root. Every record carries its provenance.
3. Definite boundaries. A read returns a value or a typed reason it is unavailable. Never a silent zero.

The node is trusted for exactly one thing: which block is canonical.

Compared with the alternatives

Indexers are the layer above balq, not a competitor: their handlers can read historical state from balq instead of an archive node.

Measured (Platåberget, 2026-08-29)

balq bench --rpc https://rpc.plataberget.ethpandaops.io --blocks 300 --top 20 — catch-up sync of the 300 latest blocks for the 20 most-written addresses on the network, release build, laptop, public gateway over HTTPS. Full tables and method: docs/BENCH.md.

The last line is the honest one: the design estimate was ~90 B/record. Reducing it is tracked, not hidden.

How it works

flowchart LR
    N[full node<br/>keeps every block] -- "eth_getBlockAccessList<br/>new blocks (sync) and<br/>old blocks (backfill)" --> C[bal-codec<br/>decode · order check<br/>keccak == header]
    C --> A[bal-archive<br/>redb · reorgs · creation]
    B[second endpoint<br/>optional] -. "old blocks the primary<br/>no longer serves, verified" .-> A
    A --> L[bal-layout<br/>solc storageLayout → names]
    L --> CLI[balq CLI]
    L --> JS["@balq/node<br/>view.balances[addr]"]

• Everything is BAL. sync reads each new block's BAL forward; backfill reads older blocks' BALs backward from the watch start. Both verify the BAL against its header and the headers against each other, so a record written from block 100,000 is as verified as one from the head. No archive node: a full node keeps every block, and the BAL is part of it.
• "What was there before?" is answered by the last earlier write (backfill finds it) or by the contract's creation: a verified BAL that shows the address receiving code proves there was no storage before it (EIP-7610), so every untouched slot is zero — a fact, not a default.
• Keys addr ‖ slot ‖ block ‖ index — a historical read is one ordered seek and a step back. A block index makes diff and rollback O(changed).
• Reorgs. Parent hashes are checked per block; a fork rolls back through the block index.
• Provenance. Every value is tagged bal, proof (optional eth_getProof shortcut), or (opt-in only) unverified / imported.

Install

cargo install balq          # CLI, from crates.io
npm i @balq/node            # Node bindings, prebuilt for win32-x64 · linux-x64 · linux-arm64 · darwin-x64 · darwin-arm64

Packages

Rust: cargo add bal-archive bal-layout — docs on docs.rs.

Use

balq index    <addr>... --rpc <url> [--layout C.json]       # the one command: watch + backfill to the deploy + follow
                                                           #   several contracts: one walk, one file; --layout 0xADDR=C.json per address
balq probe    --rpc <url>                                  # does this node serve BALs, how far back?
balq watch    <addr> [--from N | --rpc <url>]              # the parts of `index`, for scripts:
balq sync     --rpc <url> --follow                         #   forward, verified, resumes after any downtime
balq backfill <addr> --rpc <url> [--to N | --resolve]      #   backward: to the deploy, to block N, or just enough
balq get      <addr> --slot 0 --block N                    # raw slot
balq get      <addr> --layout C.json --field totals.index --block N
balq diff    <addr> --from A --to B [--layout C.json]      # names where possible, [raw] where not
balq history <addr> --slot 0 --range A..B
balq verify  --journal rows.jsonl                          # archive vs. rows you know are true
balq typegen C.json --name CView > C.d.ts                  # TypeScript for the Node view
balq bench   [--rpc <url>] [--out docs/bench]              # the numbers above
balq completions bash > /etc/bash_completion.d/balq      # zsh, fish, powershell too

Every command takes --json for scripts (a miss is {"error":{"code":"BeforeStart",…}} with exit code 2, never a zero). balq.toml holds the defaults: rpc, backup_rpc, data, and for index the watch = ["0x…", …] list, the default layout and a [layouts] table with one layout per address (a protocol of several contracts) — then it is just balq index. Run it as a service with deploy/balq.service or the Dockerfile; common errors are explained in docs/FAQ.md.

The layout is the storageLayout from your compiler (forge inspect C storageLayout, or a forge/hardhat artifact) — not the ABI.

Node

const { Archive, Layout, NotAvailableError } = require("@balq/node");
const ar = Archive.open("./balq.redb");
ar.watch(proxy, 114563);
await ar.sync(rpcUrl);                               // forward; reads keep working meanwhile
await ar.backfill(rpcUrl, proxy);                    // backward, to the deploy

const layout = Layout.fromFile("out/Playground.sol/Playground.json");
const v = ar.view(proxy, layout).at(114591);
v.counter; v.balances[addr]; v.totals.index; v.items[3]; v.items.length;   // bigint / boolean / string
try { ar.view(proxy, layout).at(1).counter } catch (e) { e.code }          // "BeforeStart", never undefined

What a read can say instead of a value

None of these happen for a contract watched from (or backfilled to) its deploy: creation seen means every value is known.

Limits, stated

• History starts at the BAL fork. Blocks before Glamsterdam carry no BAL; a contract that already lived then keeps its pre-fork storage unknown unless proven against an archive node (sync --prove, or --backup-rpc). Contracts deployed after the fork have complete history.
• The node must still serve old blocks. Backfill reads them; a node with history expiry (EIP-4444) answers HistoryUnavailable — pass --backup-rpc with any endpoint that still has them. It is asked for blocks only, and verified like the primary.
• Mappings cannot be enumerated (keccak is one-way); reading a known key works, "list all holders" does not.
• Not yet: header self-hash check, subscribe() stream, ERC-7201 / Diamond layouts, long bytes/string.
• EIP-7928 is in Review. The wire format lives in one crate and is pinned by a known-answer test against a real block; a spec change touches one file and fails that test first.

Repository

crates/            bal-codec · bal-source · bal-archive · bal-layout · bal-cli · bal-node
docs/              SPEC.md · DECISIONS.md · BENCH.md · SECURITY-AUDIT.md · bench/
testbed/           own contract on Platåberget + journal = ground truth for `verify` (96/96)
.github/           ci: fmt · clippy · rustdoc · tests on 3 OSes · MSRV · live probe; npm prebuilds

MSRV 1.90. Workspace lints: missing_docs, unwrap_used, unsafe_code = deny. CHANGELOG.md · CONTRIBUTING.md · SECURITY.md · MIT OR Apache-2.0.