yelno.ai
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MCP & agents / A2A

A2A agents

Reach the gateway from other agents over the Agent2Agent protocol: an Agent Card for discovery, tasks for every message, the final price on every run.

POST/v1/a2ainference:invoke

Yelno answers Agent2Agent (A2A 0.3) JSON-RPC requests as an agent with one skill, chat: it runs your message on the model you name, under your organization's routing policy, guardrails, limits and balance, and charges it at the model's final price. Every run is an ordinary request; its id is in the task's metadata.yelno.request_ids.

Agent Card

Agents discover Yelno at https://yelno.ai/.well-known/agent-card.json (also served at /.well-known/agent.json). The card is public; every call to the endpoint needs an API key as a bearer token.

Send a message

Name the model in metadata.model (a model id from GET /v1/models). Text parts are sent as text and data parts as JSON text. To continue a conversation, send the next message with the same contextId: earlier tasks of that context are included as history while their content is kept.

Send a message
curl https://yelno.ai/v1/a2a \
  -H "Authorization: Bearer $YELNO_API_KEY" -H "Content-Type: application/json" \
  -d '{"jsonrpc": "2.0", "id": 1, "method": "message/send", "params": {
        "message": {"role": "user", "messageId": "m-1",
                    "parts": [{"kind": "text", "text": "Summarize this ticket: ..."}]},
        "metadata": {"model": "MODEL"}}}'
Task
{
  "kind": "task", "id": "a2at_…", "contextId": "a2ac_…",
  "status": {"state": "completed", "timestamp": "…"},
  "history": [{"role": "user", "parts": [{"kind": "text", "text": "Summarize this ticket: ..."}], …}],
  "artifacts": [{"artifactId": "a2at_…-answer", "name": "answer", "parts": [{"kind": "text", "text": "…"}]}],
  "metadata": {"yelno": {"model": "MODEL", "request_ids": ["req_…"], "content_retained": true,
                         "expires_at": "…", "cost": {"state": "final", "currency": "USD", "amount": "0.000412"}}}
}

Methods

MethodWhat it does
message/sendRun a message and return the task. configuration.blocking: false returns at once; poll tasks/get.
message/streamThe same over server-sent events: the task, working, answer chunks as artifact updates, then the final status with the charge.
tasks/getA task by id, with historyLength to trim its history.
tasks/cancelStop a task that has not ended; usage up to that point is charged.
not offeredPush notifications (-32003), tasks/resubscribe and continuing an ended task (-32004), file parts (-32005).

A task refused before any model ran (your policy, balance, budget, rate limit or a guardrail) ends rejected; a provider failure ends failed. Either way status.message says why and metadata.yelno.error_code names it.

What is stored, and for how long

  • A task's state, model and request ids are kept for 24 hours, then deleted with everything else about the task.
  • The task's messages and answer are kept encrypted for that time so tasks/get can return them, and only when your organization allows content to be kept. If your policy requires zero data retention or a retention ceiling of 0 days, no content is stored: the answer comes back only in the response that produced it, and the task says content_retained: false.