> ## Documentation Index
> Fetch the complete documentation index at: https://docs.uniblock.dev/llms.txt
> Use this file to discover all available pages before exploring further.

# Data polyfill

> Automatic data completion across providers when gaps or outages occur.

# What is data polyfill?

Data polyfill automatically fills gaps in blockchain data when your primary provider has incomplete coverage. Uniblock detects missing data for specific chains, time periods, or data types and seamlessly retrieves it from alternative providers.

**Use data polyfill when you need:**

* Complete historical data across all chains
* Consistent data availability regardless of provider limitations
* Automatic handling of provider-specific gaps
* Zero manual provider switching

<Info>
  Data polyfill is enabled by default for all Uniblock users. No configuration
  required.
</Info>

***

## How it works

Uniblock continuously monitors data completeness across providers. When gaps are detected:

1. **Gap detection** - System identifies missing or incomplete data from primary provider
2. **Provider selection** - Automatically selects best alternative provider for the missing data
3. **Data retrieval** - Fetches complete data from backup provider
4. **Unified response** - Returns complete dataset to your application

**Result:** You always get complete data without manual provider switching.

***

## Polyfill scenarios

### Missing chain coverage

**Scenario:** Provider A has Ethereum data but missing Polygon data.

**What happens:**

1. Request for Polygon token balances sent to Provider A
2. Provider A returns no data or error
3. Uniblock detects missing Polygon coverage
4. Request automatically routes to Provider B (has Polygon data)
5. Complete Polygon data returned to your application

```bash Request with automatic chain polyfill theme={null}
curl --location \
'https://api.uniblock.dev/uni/v1/token/balances?chainId=137&address=0x742d35Cc6634C0532925a3b844Bc9e7595f0bEb' \
--header 'x-api-key: YOUR_API_KEY'
```

**Result:** Seamless access to Polygon data even when primary provider doesn't support it.

### Historical data gaps

**Scenario:** Provider C has recent transactions but missing historical data.

**What happens:**

1. Request for transactions from 2020 sent to Provider C
2. Provider C returns only data from 2022 onwards
3. Uniblock detects historical gap (2020-2021)
4. Backfills missing period from Provider D
5. Complete historical dataset returned

```bash Request with automatic historical backfill theme={null}
curl --location \
'https://api.uniblock.dev/uni/v1/transactions?chainId=1&address=0x742d35Cc6634C0532925a3b844Bc9e7595f0bEb&startDate=2020-01-01&endDate=2023-12-31' \
--header 'x-api-key: YOUR_API_KEY'
```

**Result:** Complete transaction history without gaps or missing periods.

### Incomplete metadata

**Scenario:** Provider E returns incomplete NFT metadata.

**What happens:**

1. Request for NFT details sent to Provider E
2. Provider E returns basic data but missing image URLs and attributes
3. Uniblock detects incomplete metadata
4. Enriches response with metadata from Provider F
5. Complete NFT data with all fields returned

```bash Request with automatic metadata enrichment theme={null}
curl --location \
'https://api.uniblock.dev/uni/v1/nft/metadata?chainId=1&contractAddress=0xBC4CA0EdA7647A8aB7C2061c2E118A18a936f13D&tokenId=1' \
--header 'x-api-key: YOUR_API_KEY'
```

**Response with polyfilled metadata:**

```json theme={null}
{
  "tokenId": "1",
  "name": "Bored Ape #1",
  "description": "The Bored Ape Yacht Club...",
  "image": "ipfs://QmRRPWG96cmgTn2qSzjwr2qvfNEuhunv6FNeMFGa9bx6mQ",
  "attributes": [
    {
      "trait_type": "Background",
      "value": "Orange"
    },
    {
      "trait_type": "Eyes",
      "value": "Bored"
    }
  ]
}
```

**Result:** Complete NFT metadata without manual enrichment.

***

## Unified backup

If your primary provider experiences an outage, Uniblock seamlessly switches to backup providers without returning errors to your application.

**Failover chain example:**

1. Primary: Alchemy (fastest, most reliable)
2. Backup 1: QuickNode (high reliability)
3. Backup 2: Ankr (stable fallback)

**Typical failover time:** \< 500ms

<Frame caption="Automatic failover across providers">
  <img src="https://mintcdn.com/uniblock/uPcmKAfw2UCOwfSR/images/docs/cfd1285-image.png?fit=max&auto=format&n=uPcmKAfw2UCOwfSR&q=85&s=6fc025735349bdc80500a763acdfb571" width="1963" height="992" data-path="images/docs/cfd1285-image.png" />
</Frame>

***

## Common polyfill scenarios

### Multi-chain applications

**Challenge:** Building a portfolio tracker that supports 20+ chains, but no single provider covers all chains.

**Solution:** Uniblock automatically routes each chain to the provider with best coverage:

* Ethereum → Alchemy
* Polygon → Covalent
* Arbitrum → QuickNode
* Base → Moralis

**Your code:**

```bash Single request, multiple providers behind the scenes theme={null}
curl --location \
'https://api.uniblock.dev/uni/v1/portfolio?address=0x742d35Cc6634C0532925a3b844Bc9e7595f0bEb&chainIds=1,137,42161,8453' \
--header 'x-api-key: YOUR_API_KEY'
```

**Result:** Complete portfolio data across all chains from a single API call.

### Historical analytics

**Challenge:** Analyzing token transfers over 3 years, but provider only has 1 year of history.

**Solution:** Uniblock automatically:

1. Fetches recent data (last year) from primary provider
2. Backfills older data (2+ years ago) from archival provider
3. Merges datasets into single response

**Result:** Complete historical dataset without manual data stitching.

### NFT marketplaces

**Challenge:** Displaying NFT collections with complete metadata, but providers have inconsistent metadata quality.

**Solution:** Uniblock automatically:

1. Fetches basic NFT data from primary provider
2. Enriches with high-quality metadata from specialized NFT providers
3. Returns complete NFT details with images, attributes, and rarity

**Result:** Rich NFT displays without multiple API calls or manual enrichment.

***

## Key benefits

<CardGroup cols={2}>
  <Card title="Complete data coverage" icon="database">
    Access all chains and historical periods without provider limitations.
  </Card>

  <Card title="Automatic gap filling" icon="puzzle-piece">
    Missing data automatically retrieved from alternative providers.
  </Card>

  <Card title="Zero configuration" icon="wand-magic-sparkles">
    Works automatically - no setup or manual provider management.
  </Card>

  <Card title="Consistent responses" icon="check-double">
    Always receive complete datasets regardless of provider gaps.
  </Card>
</CardGroup>

***

## Monitoring polyfill activity

Track polyfill events in the Uniblock dashboard:

* **Polyfill count** - How many times data was filled from backup providers
* **Gap types** - Chain coverage, historical data, or metadata gaps
* **Provider usage** - Which providers are filling which gaps
* **Data completeness** - Percentage of requests requiring polyfill

**Insights available:**

* Identify which chains require most polyfilling
* Understand historical data coverage across providers
* Optimize provider selection based on your data needs

***

## Best practices

<Check>
  **Request all needed data in single calls** - Uniblock handles multi-provider
  routing automatically. Don't split requests unnecessarily.
</Check>

<Check>
  **Use date ranges for historical queries** - Specify exact date ranges to help
  Uniblock optimize provider selection for historical data.
</Check>

<Check>
  **Monitor polyfill patterns** - Review dashboard to understand which data
  types require most polyfilling. This helps optimize your data strategy.
</Check>

<Check>
  **Trust the automation** - Don't manually switch providers or implement
  fallback logic. Uniblock handles this more efficiently.
</Check>

***

## Next steps

<CardGroup cols={2}>
  <Card title="Backup providers" icon="shield-check" href="/guides/uniblock/autorouting/uniblock-backup">
    Learn how backup providers ensure high availability.
  </Card>

  <Card title="Auto-retry" icon="rotate" href="/guides/uniblock/autorouting/uniblock-auto-retry">
    Understand automatic retry logic for failed requests.
  </Card>

  <Card title="Routing optimization" icon="gauge-high" href="/guides/uniblock/autorouting/uniblock-routing-optimization">
    Optimize provider selection for cost and performance.
  </Card>

  <Card title="Dashboard" icon="chart-line" href="https://dashboard.uniblock.dev">
    Monitor polyfill activity and data completeness.
  </Card>
</CardGroup>

***

## Common pitfalls

<Warning>
  **Don't assume single-provider responses** - Polyfilled responses may combine
  data from multiple providers. This is expected and ensures completeness.
</Warning>

<Warning>
  **Data format consistency** - While Uniblock normalizes responses, minor
  differences may exist between providers. Test thoroughly with your data
  models.
</Warning>

<Warning>
  **Historical data limits** - Some chains have limited historical data across
  all providers. Uniblock polyfills where possible but can't create data that
  doesn't exist.
</Warning>

<Warning>
  **Metadata quality variance** - NFT metadata quality varies by provider.
  Uniblock selects best available sources but metadata completeness depends on
  original sources.
</Warning>