{"openapi":"3.1.0","info":{"title":"A2A Callback Mailbox by InversoLabs","version":"0.1.54","description":"Machine-payable capabilities for autonomous agents. This service accepts A2A callback payloads but is not itself an A2A protocol server and does not publish an A2A Agent Card.","x-a2a-compatibility":{"mode":"callback-ingress","agentCard":false,"mediaType":"application/a2a+json"},"x-guidance":"Use createTemporaryA2aCallbackInbox when an agent needs a short-lived, authenticated public HTTPS callback for asynchronous A2A or webhook task completion. Purchase once per mailbox; callback messages are included. Send an Idempotency-Key when supported, inspect the HTTP 402 PAYMENT-REQUIRED challenge, settle the advertised x402 terms, and retry the identical request with PAYMENT-SIGNATURE. Proxies that cannot forward custom headers are replay-safe because Foundry derives idempotency from the signed payment proof."},"servers":[{"url":"https://callbacks.inversolabs.us"}],"paths":{"/v1/services/agent-callback-mailbox/invoke":{"post":{"operationId":"createTemporaryA2aCallbackInbox","summary":"Create a temporary private authenticated webhook inbox for asynchronous A2A task completion. Let an expensive reasoning agent suspend instead of spending model calls polling for completion; a lightweight worker can receive and persist the callback, then resume the agent when useful data exists. One payment includes up to 1,000 ordered callback messages, replay-safe deduplication, cursor retrieval, a configurable 1-minute to 24-hour lifetime, and up to 4 MiB storage.","description":"Buy a temporary authenticated callback URL instead of deploying webhook infrastructure. Designed for autonomous agents waiting for asynchronous A2A task completion. One mailbox purchase includes multiple ordered messages, cursor retrieval, deduplication, configurable expiry, and bounded private storage; callbacks are not billed per message.","tags":["agents","a2a","callback","webhook","inbox","async","task-completion"],"x-price":"$0.005","x-payment-info":{"price":{"mode":"fixed","currency":"USD","amount":"0.005"},"protocols":[{"x402":{}}]},"x-x402-price":{"amount":"0.005","currency":"USDC","network":"eip155:8453","networks":["solana:5eykt4UsFv8P8NJdTREpY1vzqKqZKvdp","eip155:8453"]},"x-agent-build-vs-buy":{"basis":"foundry_estimate","estimatedRecreationCostUsd":"4.0","estimatedRecreationTimeMinutes":240,"estimatedRecreationFailureProbability":0.25,"purchasePriceUsd":"0.005","customerSavingsRatio":"800.0","recreationResistanceScore":15,"estimateUpdatedAt":"2026-08-20T12:20:00+00:00"},"parameters":[{"name":"Idempotency-Key","in":"header","required":false,"description":"Recommended stable caller key. If omitted on the paid retry, Foundry derives a replay-safe identity from PAYMENT-SIGNATURE.","schema":{"type":"string","minLength":8,"maxLength":128}}],"requestBody":{"required":true,"content":{"application/json":{"schema":{"type":"object","properties":{"expectedTaskId":{"type":"string","minLength":1,"maxLength":256},"ingressCredential":{"type":"string","minLength":32,"maxLength":256},"retrievalCredential":{"type":"string","minLength":32,"maxLength":256},"ttlMinutes":{"type":"integer","minimum":1,"maximum":1440},"maxEvents":{"type":"integer","minimum":1,"maximum":1000},"maxBytes":{"type":"integer","minimum":65536,"maximum":4194304}},"required":["expectedTaskId","ingressCredential","retrievalCredential"],"additionalProperties":false},"example":{"expectedTaskId":"task-123","ingressCredential":"CALLER_GENERATES_RANDOM_32_PLUS_CHARS","retrievalCredential":"CALLER_GENERATES_DIFFERENT_32_CHARS"}}}},"responses":{"200":{"description":"Mailbox provisioned after successful settlement","content":{"application/json":{"schema":{"type":"object","properties":{"mailbox_id":{"type":"string"},"callback_url":{"type":"string"},"authentication_scheme":{"type":"string"},"expires_at":{"type":"string"},"max_events":{"type":"integer"},"max_bytes":{"type":"integer"}},"required":["mailbox_id","callback_url","authentication_scheme","expires_at","max_events","max_bytes"],"additionalProperties":false},"example":{"mailbox_id":"example-mailbox-id","callback_url":"https://callbacks.inversolabs.us/callbacks/example-mailbox-id","authentication_scheme":"Bearer","expires_at":"2026-08-20T14:00:00+00:00","max_events":100,"max_bytes":1048576}}}},"402":{"description":"x402 v2 payment challenge; inspect PAYMENT-REQUIRED header"},"422":{"description":"Input failed schema validation"},"503":{"description":"Service unavailable or execution failed"}}}},"/callbacks/{mailbox_id}":{"post":{"operationId":"deliverCallbackEvent","summary":"Deliver an authenticated callback event to a purchased mailbox","description":"Accepts JSON webhook events, including A2A task/status callback payloads. This compatibility endpoint is not an A2A message/send or task server.","tags":["callback","a2a","delivery"],"security":[{"bearerAuth":[]}],"parameters":[{"name":"mailbox_id","in":"path","required":true,"schema":{"type":"string"}}],"requestBody":{"required":true,"content":{"application/a2a+json":{"schema":{"type":"object","additionalProperties":true,"description":"A JSON callback event; A2A task/status payloads are accepted."}},"application/json":{"schema":{"type":"object","additionalProperties":true,"description":"A JSON callback event; A2A task/status payloads are accepted."}}}},"responses":{"200":{"description":"Event accepted and durably ordered"},"400":{"description":"Malformed JSON"},"401":{"description":"Invalid ingress credential"},"404":{"description":"Mailbox not found"},"409":{"description":"Mailbox capacity reached or unavailable"},"410":{"description":"Mailbox expired"},"413":{"description":"Payload too large"},"415":{"description":"Unsupported media type"},"422":{"description":"Invalid A2A event"}}}},"/v1/callback-mailboxes/{mailbox_id}/events":{"get":{"operationId":"listCallbackEvents","summary":"Retrieve ordered callback events from a purchased mailbox","tags":["callback","events"],"security":[{"bearerAuth":[]}],"parameters":[{"name":"mailbox_id","in":"path","required":true,"schema":{"type":"string"}},{"name":"after","in":"query","schema":{"type":"integer","minimum":0,"default":0}},{"name":"limit","in":"query","schema":{"type":"integer","minimum":1,"maximum":100,"default":100}}],"responses":{"200":{"description":"Ordered events and cursor metadata"},"400":{"description":"Invalid cursor or limit"},"401":{"description":"Invalid retrieval credential"},"404":{"description":"Mailbox not found"}}},"delete":{"operationId":"deleteCallbackMailbox","summary":"Delete a mailbox and its events","tags":["callback","lifecycle"],"security":[{"bearerAuth":[]}],"parameters":[{"name":"mailbox_id","in":"path","required":true,"schema":{"type":"string"}}],"responses":{"200":{"description":"Mailbox deleted"},"401":{"description":"Invalid retrieval credential"},"404":{"description":"Mailbox not found"}}}}},"components":{"securitySchemes":{"bearerAuth":{"type":"http","scheme":"bearer","description":"Caller-generated ingress or retrieval credential returned at provisioning."}}},"externalDocs":{"url":"https://callbacks.inversolabs.us/.well-known/agent-service.json"}}