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HomeDocsModel Context Protocol 29 Jul 2026
One change · mcp

SEP-2164: Standardize Resource Not Found Error Code changedseps/2164-resource-not-found-error

Upstream edited this page at 29 Jul 2026 22:46 UTC, give or take a minute or two: the time comes from Anthropic’s own sitemap rather than from a commit. This site recorded the change at 28 Sep 2026 22:07 UTC.

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2020 requirements.
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23| Field | Value |
24| ------------- | ------------------------------------------------------------------------------- |
25| **SEP** | 2164 |
26| **Title** | Standardize Resource Not Found Error Code |
27| **Status** | Final |
28| **Type** | Standards Track |
29| **Created** | 2026-01-28 |
30| **Author(s)** | Peter Alexander ([@pja-ant](https://github.com/pja-ant)) |
31| **Sponsor** | None (seeking sponsor) |
32| **PR** | [#2164](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/2164) |
23| Field | Value |
24| - | - |
25| **SEP** | 2164 |
26| **Title** | Standardize Resource Not Found Error Code |
27| **Status** | Final |
28| **Type** | Standards Track |
29| **Created** | 2026-01-28 |
30| **Author(s)** | Peter Alexander ([@pja-ant](https://github.com/pja-ant)) |
31| **Sponsor** | None (seeking sponsor) |
32| **PR** | [#2164](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/2164) |
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4343 
4444Current SDK implementations vary in their error handling for resource not found:
4545 
46| SDK | Current Error Code | Source |
47| ---------- | -------------------------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
48| TypeScript | `-32602` (InvalidParams) | [mcp.ts#L561](https://github.com/modelcontextprotocol/typescript-sdk/blob/main/packages/server/src/server/mcp.ts#L561) |
49| Python | `0` (generic) | [server.py#L790](https://github.com/modelcontextprotocol/python-sdk/blob/main/src/mcp/server/lowlevel/server.py#L790) |
50| C# | `-32002` (custom RESOURCE\_NOT\_FOUND) | [McpServerImpl.cs#L289](https://github.com/modelcontextprotocol/csharp-sdk/blob/main/src/ModelContextProtocol.Core/Server/McpServerImpl.cs#L289) |
51| Rust | `-32002` (custom RESOURCE\_NOT\_FOUND) | [model.rs#L450](https://github.com/modelcontextprotocol/rust-sdk/blob/main/crates/rmcp/src/model.rs#L450) |
52| Java | `-32002` (custom RESOURCE\_NOT\_FOUND) | [McpAsyncServer.java#L732](https://github.com/modelcontextprotocol/java-sdk/blob/main/mcp-core/src/main/java/io/modelcontextprotocol/server/McpAsyncServer.java#L732) |
53| Go | `-32002` (custom RESOURCE\_NOT\_FOUND) | [server.go#L786](https://github.com/modelcontextprotocol/go-sdk/blob/main/mcp/server.go#L786) |
54| Kotlin | `-32603` (INTERNAL\_ERROR) | [Server.kt#L618-L621](https://github.com/modelcontextprotocol/kotlin-sdk/blob/main/kotlin-sdk-server/src/commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/server/Server.kt#L618-L621) |
55| PHP | `-32002` (custom RESOURCE\_NOT\_FOUND) | [Error.php#L37](https://github.com/modelcontextprotocol/php-sdk/blob/main/src/Schema/JsonRpc/Error.php#L37) |
56| Ruby | N/A (left to implementor) | [server.rb#L375-L379](https://github.com/modelcontextprotocol/ruby-sdk/blob/main/lib/mcp/server.rb#L375-L379) |
57| Swift | N/A (no built-in handler) | N/A |
46| SDK | Current Error Code | Source |
47| - | - | - |
48| TypeScript | `-32602` (InvalidParams) | [mcp.ts#L561](https://github.com/modelcontextprotocol/typescript-sdk/blob/main/packages/server/src/server/mcp.ts#L561) |
49| Python | `0` (generic) | [server.py#L790](https://github.com/modelcontextprotocol/python-sdk/blob/main/src/mcp/server/lowlevel/server.py#L790) |
50| C# | `-32002` (custom RESOURCE\_NOT\_FOUND) | [McpServerImpl.cs#L289](https://github.com/modelcontextprotocol/csharp-sdk/blob/main/src/ModelContextProtocol.Core/Server/McpServerImpl.cs#L289) |
51| Rust | `-32002` (custom RESOURCE\_NOT\_FOUND) | [model.rs#L450](https://github.com/modelcontextprotocol/rust-sdk/blob/main/crates/rmcp/src/model.rs#L450) |
52| Java | `-32002` (custom RESOURCE\_NOT\_FOUND) | [McpAsyncServer.java#L732](https://github.com/modelcontextprotocol/java-sdk/blob/main/mcp-core/src/main/java/io/modelcontextprotocol/server/McpAsyncServer.java#L732) |
53| Go | `-32002` (custom RESOURCE\_NOT\_FOUND) | [server.go#L786](https://github.com/modelcontextprotocol/go-sdk/blob/main/mcp/server.go#L786) |
54| Kotlin | `-32603` (INTERNAL\_ERROR) | [Server.kt#L618-L621](https://github.com/modelcontextprotocol/kotlin-sdk/blob/main/kotlin-sdk-server/src/commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/server/Server.kt#L618-L621) |
55| PHP | `-32002` (custom RESOURCE\_NOT\_FOUND) | [Error.php#L37](https://github.com/modelcontextprotocol/php-sdk/blob/main/src/Schema/JsonRpc/Error.php#L37) |
56| Ruby | N/A (left to implementor) | [server.rb#L375-L379](https://github.com/modelcontextprotocol/ruby-sdk/blob/main/lib/mcp/server.rb#L375-L379) |
57| Swift | N/A (no built-in handler) | N/A |
5858 
5959This inconsistency means clients cannot reliably detect resource-not-found conditions across implementations. Of the 8 SDKs with built-in resource handling, four different error codes are used: `-32002` (C#, Rust, Java, Go, PHP), `-32602` (TypeScript), `-32603` (Kotlin), and `0` (Python). Ruby and Swift leave error handling to the server implementor. Clients that need to distinguish "resource not found" from other errors must handle all variants.
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