---
title: MCP Servers Must Now Implement server/discover
description: The 2026-07-28 MCP spec adds a required server/discover RPC. Existing servers need a handler for it before a compliant client can negotiate at all.
date: 2026-08-06T00:00:00.000Z
category: ai-productivity
tags: mcp, model-context-protocol, agents, api
---

## Quick Answer

The MCP 2026-07-28 specification adds [a mandatory `server/discover` RPC](https://modelcontextprotocol.io/specification/2026-07-28/server/discover) that every compliant server must implement, advertising its supported protocol versions, capabilities, and identity. This is the replacement discovery path for [the removed `initialize` handshake](/ai-productivity/mcp-replaces-initialize-handshake-with-meta-fields/): any existing server implementation needs a new handler added for this method before a 2026-07-28-compliant client can safely negotiate with it.

## What's actually changing

The specification changelog states it directly:

> "Added `server/discover` RPC: Servers must implement this to advertise their supported protocol versions, capabilities, and identity; clients may call before other requests"

This closes the gap left by removing `initialize`. Previously, a client learned a server's supported version and capabilities as part of the connection handshake. With that handshake gone, `server/discover` is the explicit, callable replacement, a request a client can make at any point (typically first) to learn what it's talking to.

<Callout type="warning" title="No fallback path if this handler is missing">
  A server built before the 2026-07-28 revision, with no `initialize`
  replacement added, has no discovery mechanism at all under the new spec. This
  isn't a graceful-degradation case; it's a required capability gap that blocks
  a compliant client from negotiating safely.
</Callout>

## Structural Comparison Matrix

| Operational Aspect                          | Before (initialize handshake)             | After (2026-07-28+)                             |
| :------------------------------------------ | :---------------------------------------- | :---------------------------------------------- |
| **How a client learns server capabilities** | Connection-start handshake response       | Explicit `server/discover` call                 |
| **Is this required on the server?**         | `initialize` was implicit to the protocol | `server/discover` is an explicit, mandatory RPC |
| **When a client can call it**               | N/A, automatic at connection              | Any time, typically before other requests       |

## Fix it: add the required handler

The exact response schema for `server/discover` wasn't confirmed from a primary source with full field-level detail here; check the current MCP specification text directly for the precise shape before implementing. What's confirmed is the requirement itself and its purpose: the response needs to communicate supported protocol versions, server capabilities, and server identity, the same three categories a pre-2026-07-28 `initialize` response would have returned from the server side.

```bash title="audit existing servers for this gap"
grep -rln "\"method\": \"initialize\"" --include="*.py" --include="*.ts" --include="*.mjs" .
```

If a server codebase only ever implemented `initialize` and never added a `server/discover` handler, that's the concrete gap to close. Cross-reference against the current SDK version for your language; the official Tier 1 SDKs updated for this revision should already expose the right interface to implement against, rather than hand-rolling the RPC from scratch.

## Confirmed version

Sourced from the official Model Context Protocol specification changelog, 2026-07-28 revision, published 2026-07-28. The requirement itself and its stated purpose are confirmed verbatim; the exact response field names weren't independently verified against a full schema reference, so confirm those against the live spec before implementing. Browse more posts like this in the [AI Productivity](/ai-productivity) archive.