API overview

Network	Base URL
Mainnet	https://api.stxer.xyz
Testnet	https://testnet-api.stxer.xyz

Both networks serve the same paths. The live OpenAPI description is at /openapi.json, browsable at /docs.

Conventions

• No keys. No authentication; please identify your client.
• JSON request and response bodies (content-type: application/json), except traces, which are binary (application/octet-stream).
• CORS is open (access-control-allow-origin: *), so browsers can call the API directly.
• Clarity values are hex-serialized strings, without 0x in responses. STX balances and nonces in reads are decimal strings. Large integers (u64, u128) may arrive as numbers or strings; parse them as BigInt.
• Ids: transaction ids and block hashes are 32-byte hex. Simulation ids are 32 hex characters.

Errors

Errors carry a plain-text body.

Status	Meaning	What to do
400	Malformed request: bad step, principal or contract id, or an AdvanceBlocks argument out of bounds	Fix the request
404	Unknown route or resource, or no trace for that transaction	Check ids; see traces
409	Body starts simulation_busy: — another submit is running on the session	Retry the same request after a short wait
410	Body starts simulation_outdated: — the session predates a simulator format change	Start a new session

Do not parse error text beyond those prefixes. Back off on 429 and 5xx.

Endpoints

Method	Path	Page
POST	/devtools/v2/simulations	Sessions
POST	/devtools/v2/simulations/{id}	Sessions
GET	/devtools/v2/simulations/{id}	Sessions
GET	/devtools/v2/simulations/{id}/tip	Sessions
POST	/devtools/v2/simulations/{id}/reads	Sessions
POST	/devtools/v2/simulations:instant	Instant
GET	/inspect/{block_height}/{block_hash}/{txid}	Traces
GET	/devtools/v2/simulations/{id}/inspect/{txid}	Traces
GET	/contracts/{contract_id}	Contracts
GET	/contracts/by-deploy/{txid}	Contracts
POST	/contracts:parse	Contracts