> ## Documentation Index > Fetch the complete documentation index at: https://docs.ag-ui.com/llms.txt > Use this file to discover all available pages before exploring further. # Run Input > The one message that travels from the application to the agent, and what each of its fields obliges — draft **Draft — not yet ratified.** This document is published for review. It describes the intended 1.0 behaviour, its wording is not final, and nothing here is covered by a compatibility promise until a version is frozen. Do not cite it as a stable reference. Events flow from producer to consumer. Exactly one message flows the other way: `RunAgentInput`, sent once to open each exchange. Everything the producer knows about the conversation arrives through it. The run it requests is the exchange's last; a stream that replays a thread's history carries the earlier runs [without further input](/spec/draft/basic/transports#the-binding-contract). The [schema](/spec/draft/schema#runagentinput) defines its shape; this page states what each field obliges. A producer MAY echo the input back on `RUN_STARTED.input`, so a consumer that did not make the request can still see what the agent was asked. ## Identity `threadId` names the conversation and `runId` names the run this input requests; both are REQUIRED. Every run on the stream carries the input's `threadId` on its boundary events — `RUN_STARTED` and `RUN_FINISHED`, the two that carry identity — and each run's two boundary events MUST agree on their `runId`. The requested run echoes this input's `runId`; a replayed run carries its own. `parentRunId` is OPTIONAL and names the run that spawned this one, when an agent starts another agent as a separate run. ## `protocolVersion` OPTIONAL in the schema, because absence identifies a peer from before the protocol carried a version — but a consumer implementing this version MUST declare the version it speaks here, unless it knows its peer predates the field and omits the member rather than risk an old parser rejecting it. The producer answers with its own declaration on `RUN_STARTED`; the rules are in [Versioning](/spec/draft/basic/versioning#version-negotiation). ## `messages` REQUIRED. The conversation so far, in order. A producer MUST treat it as the complete history it is being shown — the protocol has no side channel through which earlier turns arrive. The message types and their content shapes — including multimodal `InputContent` parts carrying text, images, audio, video and documents by URL or inline data — are the schema's business. Two behavioural rules attach: * A producer that cannot use a content part — a model without vision handed an image — MUST NOT fail the run because of it. Skipping what it cannot use and continuing is the conforming behaviour; losing content on a downgraded *outgoing* path is different and obliges a warning ([Versioning](/spec/draft/basic/versioning)). * Activity messages never travel back to the producer: a consumer MUST strip them from `messages` before sending. They are the consumer's rendering material, not conversation the agent resumes from. ## `tools` OPTIONAL. The application's own tools — *frontend tools* — offered to the agent for this run: name, description and, where the tool takes arguments, a parameter schema. The application executes them, not the agent; calling one hands control back across the run boundary, the round-trip [Tool calls](/spec/draft/events/tool-calls#frontend-tools) specifies. An absent list and an empty list mean the same thing: no tools. A producer MUST treat a missing `tools` exactly as it would treat an empty one, and a consumer MAY omit an empty list rather than sending `[]`. ## `context` OPTIONAL. Information the application wants in the agent's context, as description–value pairs. It exists to be *injected*: a producer SHOULD make every entry available to the model as part of the run's grounding. How — a system prompt, a preamble, whatever the framework does with context — is the producer's business; the protocol says only that context is for the model to see, not bookkeeping for the transport. Absence means the same as emptiness, exactly as for `tools`. ## `state` OPTIONAL. The state the run starts from — the consumer's last agreed value, typically what the previous run's [state events](/spec/draft/events/state) left behind. An absent `state` means the empty object: nothing has been agreed, and `{}` is nothing. A producer that emits state deltas MUST compute them against this value until its own first snapshot replaces it. ## `forwardedProps` OPTIONAL. An application-specific channel passed through to the agent untouched. Any JSON value. The protocol attaches no meaning to it, and intermediaries MUST NOT alter it. ## `resume` OPTIONAL. Answers to the interrupts that ended a previous run, when this run continues from one. The entries and their obligations are specified in [Interrupts and Resume](/spec/draft/basic/patterns/interrupt-resume). ## Error Handling An input a producer cannot parse, or that is malformed — a known field carrying a value the schema rejects — is rejected before `RUN_STARTED`, through the transport's error path: the run never starts, and no stream exists for a `RUN_ERROR` to travel on. How the rejection is delivered is each [transport binding](/spec/draft/basic/transports)'s business. Unrecognised members of the input are not malformed. The [processing model](/spec/draft/basic/processing)'s asymmetry binds this direction too: a producer meeting input material it does not recognise strips it with a warning and runs, so a newer consumer's input does not bounce off an older producer.