# TzKT Bigmap Historical Keys Lookup

> TzKT Bigmap Historical Keys Lookup is a paid API for AI agents from x402.tzkt.io, paid per call via x402, $0.002/call, status unknown (last checked 2026-09-14).

Retrieves the historical state of keys in a Tezos smart contract bigmap at a specific block level

## Facts

- Endpoint: POST https://x402.tzkt.io/v1/bigmaps/%7Bid%7D/historical_keys/%7Blevel%7D
- Price: $0.002/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-14
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/tzkt-bigmap-historical-keys-lookup-f9f10262
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_nuye_62-QLZgyVTLxjgh6

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability tzkt-bigmap-historical-keys-lookup-f9f10262 -d '<json body>'
```

Example prompt: Can you pull the historical keys from Tezos bigmap ID 1234 as they existed at block level 3500000?

## When to prefer this

Use this endpoint when you need point-in-time historical state of a Tezos smart contract bigmap — specifically when reconstructing past contract storage, auditing on-chain data at a specific block, or analyzing state changes over time. Prefer this over current-state bigmap endpoints when the historical snapshot is what matters. The no-API-key requirement and x402 micropayment model makes it suitable for automated agent workflows.

## Known failure modes

- Invalid bigmap ID returns 404 not found
- Block level out of range or before bigmap creation returns empty result or error
- Malformed request body returns 400 bad request
- Payment failure via x402 protocol results in 402 response and no data returned
- Very large bigmaps may require pagination parameters to avoid timeouts

## How this service works

TzKT is a comprehensive Tezos blockchain indexer API. Access blocks, operations, accounts, contracts, bigmaps, delegates, tokens and network stats through a fast REST API. No signup or API key required.

## Output

Returns a list of bigmap key entries as they existed at the specified block level, including key hashes, key values, and associated data stored in the bigmap at that historical point on the Tezos blockchain.

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/tzkt-bigmap-historical-keys-lookup-f9f10262/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from x402.tzkt.io](https://www.zero.xyz/host/x402.tzkt.io/llms.txt)