BracketAgent Client Protocol (ACP) Message Validator
Paste a JSON-RPC message and check it against the Agent Client Protocol (ACP) — the Zed-originated, now multi-vendor standard for editor-to-coding-agent communication. Validates the initialize handshake and the session/new, session/prompt, session/cancel, and session/update baseline methods every agent must support. 100% client-side.
🔒 Runs entirely in your browser — no data is ever sent anywhereWhat the Agent Client Protocol is
ACP standardizes how a code editor talks to a coding agent over JSON-RPC 2.0, the same role LSP plays for language servers — instead of every editor writing a bespoke integration for every agent, both sides speak one protocol. Originated by Zed and now at a stable v1.0 with adopters including JetBrains, Gemini CLI, GitHub, and 25+ other agents, it defines a one-time initialize handshake to negotiate protocol version and capabilities, then a session-based loop (session/new to start, session/prompt to send a turn, session/update notifications streaming the agent's response back, session/cancel to interrupt) plus client-side callbacks an agent can invoke — reading/writing files, running a terminal, asking the user for permission before a risky action.
What this tool checks — and where the depth stops
This validates the JSON-RPC envelope (jsonrpc: "2.0", correct request/notification/response shape) against the published, stable ACP v1 schema, and does deep field-level validation for the handshake and the four methods every agent MUST support per spec (session/new, session/prompt, session/cancel, session/update), plus the common client-capability methods (authenticate, session/request_permission, fs/read_text_file, fs/write_text_file). A frequent real mistake it catches: protocolVersion is an integer (currently 1), not a date-like string the way some other AI protocols format their version field. Every other recognized ACP method (session/load, session/fork, provider management, terminal control, the newer nes/* and document/* extensions) is checked against the full method table so a typo is still caught, just without field-level depth. It can't validate a bare JSON-RPC response ({ id, result }) against its method-specific shape, since a response alone doesn't name which request it's answering — paste the request instead to check what shape the response should have.
Frequently asked questions
What is the Agent Client Protocol (ACP)?
A JSON-RPC 2.0 protocol, originated by Zed and now at a stable v1.0, that standardizes communication between code editors and AI coding agents — the same role the Language Server Protocol (LSP) plays for language servers. It defines an initialize handshake, a session-based prompt loop (session/new, session/prompt, session/update, session/cancel), and client-side capabilities an agent can invoke like file access, terminal execution, and permission requests.
Why is my protocolVersion being rejected?
ACP's protocolVersion is an unsigned 16-bit integer (currently 1 for the stable spec), not a string. A common mistake when coming from other AI protocols that use a date-like version string is sending "1" as text or a date such as "2026-06-24" — both fail validation, since the field must be a genuine JSON number.
Which methods does this check in full field-level detail?
The initialize handshake, and the four baseline methods every ACP agent must implement per spec: session/new, session/prompt, session/cancel, and session/update — plus authenticate, session/request_permission, fs/read_text_file, and fs/write_text_file. Other recognized ACP methods (session management extras, provider/terminal/document handling, the newer nes/* edit-suggestion methods) are checked against the full method table so a typo or wrong-direction method is still caught, just without validating their specific parameter shapes.
Can this validate a response message?
Only its JSON-RPC envelope — that it has exactly one of result or error, and that an error object carries a numeric code and string message. It can't check a response's result against its method-specific shape (e.g. that a session/new response actually has a sessionId), because a bare response has no method field to identify which request it's answering. Paste the originating request instead to see what shape its response needs.
Is my pasted message sent anywhere?
No. Parsing and validation both run locally in your browser using plain JavaScript, checked against the published stable ACP v1 JSON schema — nothing you paste is transmitted or stored.
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