Imported from jiayaoqijia/cryptoskill (skills/chains/cardano-foundation-query-chain/SKILL.md). Install upstream with npx skills add jiayaoqijia/cryptoskill --skill cardano-foundation-query-chain. Copyright stays with the author.

Query Cardano Chain Data

Help the developer choose and use the right data provider for querying the Cardano blockchain.

When to use

• Developer needs to read UTxOs, transaction history, protocol parameters, or on-chain state
• Choosing between Blockfrost, Ogmios, Kupo, Koios, Cardano GraphQL, DB-Sync, or Oura
• Setting up a data pipeline from chain data
• Querying datum or script information attached to UTxOs
• Building a backend service that needs chain data
• Comparing hosted vs self-hosted infrastructure options

When NOT to use

• Building or submitting transactions (use transaction-building skills instead)
• Setting up a local devnet (use setup-devnet skill)
• Writing smart contracts (use Aiken/Plutus skills)
• Wallet integration in a frontend (use connect-wallet skill)

Key principles

1. Match the provider to the use case. There is no single best provider. A dApp frontend has different needs than a data pipeline.
2. Hosted APIs are faster to start; self-hosted gives control. Blockfrost and Koios are hosted. Ogmios, Kupo, DB-Sync require running infrastructure.
3. Combine providers when needed. Ogmios + Kupo is a common pairing: Ogmios for tx submission and protocol params, Kupo for UTxO queries.
4. Consider cost at scale. Hosted APIs have rate limits and pricing tiers. Self-hosted has infrastructure cost.
5. Think about latency requirements. WebSocket (Ogmios) is lower latency than REST (Blockfrost). Local node queries are fastest.

Workflow

Step 1: Identify the context

Ask the developer (if not already clear):

• What are you building? (backend-service | dapp-frontend | data-pipeline | one-off-query)
• Do you need real-time chain-tip data or historical queries?
• Are you running your own Cardano node?
• What language/SDK are you using?

Step 2: Search Bundled Documentation

Search the bundled documentation for relevant content:

• ${CLAUDE_SKILL_DIR}/../../docs/sources/ogmios/ - Ogmios WebSocket bridge docs
• ${CLAUDE_SKILL_DIR}/../../docs/sources/blockfrost-openapi/ - Blockfrost API docs
• ${CLAUDE_SKILL_DIR}/../../docs/sources/koios/ - Koios API docs
• ${CLAUDE_SKILL_DIR}/../../docs/sources/cardano-graphql/ - Cardano GraphQL docs
• ${CLAUDE_SKILL_DIR}/../../docs/sources/db-sync/ - DB-Sync docs
• ${CLAUDE_SKILL_DIR}/../../docs/sources/yaci-store/ - Yaci Store (modular JVM indexer; see stores/, plugins/, usage/as-library/)
• ${CLAUDE_SKILL_DIR}/../../docs/sources/evolution-sdk/ - Evolution SDK docs (TypeScript client; see providers/ and querying/)
• ${CLAUDE_SKILL_DIR}/../../docs/sources/blockfrost-go/ - Blockfrost Go client (typed endpoint wrappers)
• ${CLAUDE_SKILL_DIR}/../../docs/sources/utxorpc-go-sdk/ - UTxORPC Go SDK (provider-agnostic gRPC)
• ${CLAUDE_SKILL_DIR}/../../docs/sources/gouroboros/ - gOuroboros (direct node mini-protocols)
• ${CLAUDE_SKILL_DIR}/../../docs/sources/dingo/ - Dingo (Go node serving UTxORPC / Blockfrost-compatible / Mesh)
• ${CLAUDE_SKILL_DIR}/../../docs/sources/adder/ - Adder (Go event pipeline; docs/swagger.yaml for its REST surface)

Step 3: Evaluate providers for the context

Search the reference file for detailed provider comparisons.

File: skills/query-chain/references/provider-comparison.md

Quick decision guide

Step 4: Describe each viable option

For each provider that fits the developer's context, explain:

1. How to set it up -- installation, configuration, API keys
2. How to make the query -- specific API calls, endpoints, or queries
3. Code example -- using their SDK/language of choice
4. Limitations -- rate limits, missing data, latency

Step 5: Provider-specific guidance

Blockfrost (Hosted REST API)

• Sign up at blockfrost.io for a project ID
• REST API with comprehensive endpoints
• SDKs: JavaScript, Python, Rust, Go, Java, Kotlin, Swift, Elixir
• Rate limits: free tier 50k requests/day, 10 req/s sustained, 500 req burst capacity
• Great for: quick prototyping, frontend dApps, moderate traffic backends

GET /addresses/{address}/utxos
GET /txs/{hash}
GET /epochs/latest/parameters

Ogmios (Self-hosted WebSocket)

• Requires a running cardano-node
• WebSocket JSON-RPC protocol (low latency)
• Local state queries: UTxOs, protocol parameters, chain tip
• Transaction submission and evaluation
• Best for: backends co-located with a node, tx submission workflows

Kupo (Self-hosted HTTP indexer)

• Indexes UTxOs by address, asset, or datum hash
• Lightweight, fast, pattern-based matching
• REST API on top of indexed data
• Often paired with Ogmios for a complete solution
• Best for: UTxO lookups, datum resolution, asset queries

Koios (Hosted REST API, community-run)

• Free tier with generous limits
• No API key required for basic use
• Comprehensive endpoints similar to Blockfrost
• Community-maintained, decentralized backend nodes
• Best for: open-source projects, quick queries, no-signup needs

Dingo (Self-hosted node with APIs built in)

A Cardano node implementation in Go that serves the query layer itself, so one process replaces the usual node-plus-Ogmios-plus-Kupo stack:

• UTxO RPC (default port 9090), a Blockfrost-compatible REST API (3000), and Mesh / Coinbase Rosetta (8080), each enabled and bound through DINGO_PLUGINS_API_*_CONFIG_PORT
• Because the REST API is Blockfrost-compatible, existing Blockfrost client code and the mirrored Blockfrost OpenAPI spec both apply — point the client at your own host instead of the hosted service
• Storage mode is the gotcha. The client-facing APIs require storageMode: "api" (full indexing). The lighter "core" mode carries only what consensus needs and will not serve them.
• Its own README states Dingo is pre-production: testnets and devnets only, not mainnet with real funds. Treat it as a development and testnet query layer, and keep Blockfrost, Koios, or Ogmios + Kupo for anything mainnet-facing.

Cardano GraphQL (Self-hosted GraphQL)

• GraphQL interface over cardano-db-sync
• Flexible queries with relationships
• Requires DB-Sync + PostgreSQL + Hasura
• Best for: complex relational queries, custom data views

DB-Sync (Self-hosted PostgreSQL)

• Full blockchain data in PostgreSQL
• Direct SQL access to all chain data
• Heavy resource requirements (100GB+ disk, significant RAM)
• Best for: analytics, complex historical queries, data warehousing

Oura (Self-hosted pipeline)

• Event-driven pipeline from cardano-node
• Outputs to Kafka, Elasticsearch, webhooks, files
• Filters and maps chain events
• Best for: real-time event processing, data pipelines, notifications

Adder (Self-hosted pipeline, Go)

• Same shape as Oura in a Go process: an input stage follows the chain, filters narrow the stream, output stages emit it
• Inputs are chainsync (over NtC or NtN), mempool, and UTxORPC, so it can follow a node directly or ride on a UTxORPC provider; the chainsync input emits input.block, input.rollback, input.transaction, and input.governance, each with its own payload
• Outputs include webhook, push, notify, log, and Telegram
• Filters narrow by event type, address, asset fingerprint, minting policy, pool ID, or DRep ID (WithTypes, WithAddresses, WithAssetFingerprints, WithPolicies, WithPoolIds, WithDRepIds)
• Runs standalone or embeds as a library, which is the reason to pick it over Oura: a Go service can consume the event stream in-process instead of shipping it through a broker first
• Best for: Go backends reacting to chain events, webhook fan-out, alerting

Evolution SDK (TypeScript client over providers)

Not a provider — a TypeScript library that wraps Blockfrost, Kupmios, Maestro, and Koios behind one query interface, so the provider becomes a config choice rather than a code rewrite. For read-only work, build a provider-only client (no wallet attached):

import { Address, Client, preprod } from "@evolution-sdk/evolution"

const client = Client.make(preprod).withBlockfrost({
  baseUrl: "https://cardano-preprod.blockfrost.io/api/v0",
  projectId: process.env.BLOCKFROST_PROJECT_ID!,
}) // or .withKupmios(...) / .withMaestro(...) / .withKoios(...) — same query API

const utxos   = await client.getUtxos(Address.fromBech32("addr_test1..."))
const nftUtxo = await client.getUtxoByUnit(unit)          // the one UTxO holding an NFT
const datum   = await client.getDatum(datumHash)
const params  = await client.getProtocolParameters()
const { poolId, rewards } = await client.getDelegation(rewardAddress)

Query methods: getUtxos, getUtxosWithUnit, getUtxoByUnit, getUtxosByOutRef, getDatum, getDelegation, getProtocolParameters, awaitTx. Best for: TypeScript backends and dApps that want one query API independent of the underlying provider. See ${CLAUDE_SKILL_DIR}/../../docs/sources/evolution-sdk/providers/ and .../querying/.

Go clients over providers

Three Go paths, ordered by how much infrastructure you run:

• blockfrost-go — typed client for the hosted Blockfrost REST API. NewAPIClient(APIClientOptions{...}), then methods mirroring the REST surface (Transaction, TransactionUTXOs, TransactionMetadata, and the Address* / Epoch* / Pool* families). Inherits every Blockfrost trade-off above, including rate limits. Also covers IPFS and webhook signature verification.
• UTxORPC Go SDK — the role Evolution SDK plays for TypeScript: the provider becomes a config choice rather than a code rewrite, against any UTxORPC-compatible backend. Paging query helpers (GetUtxosByAddressPages, GetUtxosByAssetPages, tuned with WithSearchMaxItems / WithSearchStartToken); submit and mempool operations on UtxorpcClient (SubmitTx, EvalTx, WaitForTx, ReadMempool, WatchMempool). Best when you may switch providers later.
• gOuroboros — speaks the node's mini-protocols directly, with no intermediary. NewConnection(...), then LocalStateQuery().Client for point-in-time state (GetUTxOByAddress, GetUTxOByTxIn, GetCurrentProtocolParams, GetStakeDistribution, GetDRepState, GetProposals) or ChainSync().Client to follow the chain (GetCurrentTip, GetAvailableBlockRange, Sync). Lowest latency and no third party, but you run the node and manage the protocol lifecycle yourself.

Runnable examples ship in the mirror: ${CLAUDE_SKILL_DIR}/../../docs/sources/gouroboros/examples/state-query/main.go and .../examples/chain-sync/main.go. Because Go sources mirror .go files, Grep a method name to get its signature and doc comment.

Step 6: Provide working code

Give the developer a working code snippet for their chosen provider and language. Always include:

• Dependency installation
• Client initialization
• The specific query they need
• Error handling
• Response parsing

Step 7: Address common issues

• Stale data: Hosted APIs may lag behind chain tip by a few seconds
• Datum resolution: Not all providers return inline datums; may need separate lookup
• Pagination: Large result sets require pagination (Blockfrost pages, Kupo cursors)
• Network selection: Ensure provider is configured for the right network (mainnet/preprod/preview)
• CORS: Frontend apps need CORS-friendly endpoints or a backend proxy

References

• skills/query-chain/references/provider-comparison.md -- Detailed comparison of the providers with decision matrix
• Blockfrost docs: https://docs.blockfrost.io
• Ogmios docs: https://ogmios.dev
• Kupo docs: https://cardanosolutions.github.io/kupo
• Koios docs: https://api.koios.rest
• DB-Sync docs: https://github.com/IntersectMBO/cardano-db-sync
• Oura docs: https://github.com/txpipe/oura
• UTxORPC: https://utxorpc.org
• blockfrost-go: https://pkg.go.dev/github.com/blockfrost/blockfrost-go