# ACP elicitation (form and URL modes)

## Metadata

| Field | Value |
|---|---|
| Institute | Molodetz Institute — Research & Retrieval Division |
| Subject | cap-protocol |
| Document type | Source Dossier |
| Tier | 1 |
| Source title | ACP Elicitation |
| Source URL | https://agentclientprotocol.com/protocol/v1/elicitation.md |
| Source type | specification |
| Source date (published) | Unknown, not stated (living docs) |
| Date researched | 2026-10-18 |
| Researched by | tai (agent), model: Muse Spark, on behalf of retoor |
| Research method | direct page fetch, read in full (199 lines) |
| Confidence | High |
| Status | Active |

## Summary

Elicitation via `elicitation/create` with explicit `mode` (no MCP-style default): form mode (flat object schema, primitives plus enums, never secrets) and URL mode (out-of-band, `elicitationId` plus `elicitation/complete` notification). Responses are accept/decline/cancel with optional content; unadvertised modes get JSON-RPC -32602. Clients advertise per-mode support explicitly (`{}` means NO modes).

## Key findings

- Form mode is the ACP counterpart of CAP `cap.ask_user` (CAP cites the same JSON-Schema-subset convention); tai's driver maps form elicitations to ask_user events.
- Explicit per-mode advertisement means tai can offer form-only and stay compliant while declining URL flows.
- MCP-compatibility trap documented in-spec: empty object does NOT mean form-only here, unlike MCP's release candidate.

## Pros / strengths

- Gives ask_user a structured cross-protocol lineage (MCP elicitation to ACP to CAP), so tai's auto-answerer targets one shape.

## Cons / limitations / caveats

- URL mode is out of scope for tai (no browser/redirect handler); tai answers URL elicitations with decline, per the spec's safe-fallback rule.
- Secrets policy is agent-side; tai-as-client cannot verify an agent obeys the no-secrets-in-form rule.

## Relevance to tai

Shapes the ask_user mapping and the research auto-answerer input contract (restricted JSON Schema form).

## Changelog

| Date | Change |
|---|---|
| 2026-10-18 | Initial dossier created. |