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benbrandt merged 3 commits into from
Oct 30, 2026
Merged

docs(schema): reject duplicate stdio env names #2693

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432b05d
docs(schema): reject duplicate stdio env names
benbrandt Oct 30, 2026
e46f7d5
docs(schema): document unique stdio env names in the Rust doc
benbrandt Oct 30, 2026
1bd1cd4
docs(schema): let Agents accept duplicate env names, last one wins
benbrandt Oct 30, 2026
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6 changes: 4 additions & 2 deletions agent-client-protocol-schema/src/v2/agent.rs
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Expand Up @@ -3140,7 +3140,8 @@ pub struct McpServerStdio {
#[cfg_attr(feature = "schemars", schemars(extend("x-deserialize-default-on-null" = true)))]
#[serde(default, skip_serializing_if = "Vec::is_empty")]
pub args: Vec<String>,
/// Environment variables to set when launching the MCP server.
/// Environment variables to set when launching the MCP server. Names SHOULD be unique;
/// Agents MAY reject duplicates with `-32602`, and otherwise the last entry wins.
#[serde_as(deserialize_as = "DefaultOnNull")]
#[cfg_attr(feature = "schemars", schemars(extend("x-deserialize-default-on-null" = true)))]
#[serde(default, skip_serializing_if = "Vec::is_empty")]
Expand Down Expand Up @@ -3177,7 +3178,8 @@ impl McpServerStdio {
self
}

/// Environment variables to set when launching the MCP server.
/// Environment variables to set when launching the MCP server. Names SHOULD be unique;
/// Agents MAY reject duplicates with `-32602`, and otherwise the last entry wins.
#[must_use]
pub fn env(mut self, env: Vec<EnvVariable>) -> Self {
self.env = env;
Expand Down
6 changes: 4 additions & 2 deletions docs/protocol/v2/draft/schema.mdx
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Expand Up @@ -5035,7 +5035,8 @@ See protocol docs: [Extensibility](https://agentclientprotocol.com/protocol/v2/d
Absolute path to the MCP server executable.
</ResponseField>
<ResponseField name="env" type={<a href="#envvariable">EnvVariable[]</a>} >
Environment variables to set when launching the MCP server.
Environment variables to set when launching the MCP server. Names SHOULD be unique;
Agents MAY reject duplicates with `-32602`, and otherwise the last entry wins.
</ResponseField>
<ResponseField name="name" type={"string"} required>
Human-readable name identifying this MCP server.
Expand Down Expand Up @@ -5172,7 +5173,8 @@ See protocol docs: [Extensibility](https://agentclientprotocol.com/protocol/v2/d
Absolute path to the MCP server executable.
</ResponseField>
<ResponseField name="env" type={<a href="#envvariable">EnvVariable[]</a>} >
Environment variables to set when launching the MCP server.
Environment variables to set when launching the MCP server. Names SHOULD be unique;
Agents MAY reject duplicates with `-32602`, and otherwise the last entry wins.
</ResponseField>
<ResponseField name="name" type={"string"} required>
Human-readable name identifying this MCP server.
Expand Down
2 changes: 1 addition & 1 deletion docs/protocol/v2/draft/session-setup.mdx
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Expand Up @@ -602,7 +602,7 @@ Example stdio transport configuration:
}
```

Agents **SHOULD** launch stdio servers with the session's `cwd` as the working directory. `env` entries are added to the environment the Agent would otherwise give the process, replacing variables with the same name. Each `env` entry **MUST** have a unique `name`.
Agents **SHOULD** launch stdio servers with the session's `cwd` as the working directory. `env` entries are added to the environment the Agent would otherwise give the process, replacing variables with the same name. Each `env` entry **SHOULD** have a unique `name`. Agents **MAY** reject duplicates with `-32602`; otherwise the last entry with a given name wins.

#### HTTP Transport

Expand Down
6 changes: 4 additions & 2 deletions docs/protocol/v2/schema.mdx
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Expand Up @@ -4411,7 +4411,8 @@ See protocol docs: [Extensibility](https://agentclientprotocol.com/protocol/v2/e
Absolute path to the MCP server executable.
</ResponseField>
<ResponseField name="env" type={<a href="#envvariable">EnvVariable[]</a>} >
Environment variables to set when launching the MCP server.
Environment variables to set when launching the MCP server. Names SHOULD be unique;
Agents MAY reject duplicates with `-32602`, and otherwise the last entry wins.
</ResponseField>
<ResponseField name="name" type={"string"} required>
Human-readable name identifying this MCP server.
Expand Down Expand Up @@ -4501,7 +4502,8 @@ See protocol docs: [Extensibility](https://agentclientprotocol.com/protocol/v2/e
Absolute path to the MCP server executable.
</ResponseField>
<ResponseField name="env" type={<a href="#envvariable">EnvVariable[]</a>} >
Environment variables to set when launching the MCP server.
Environment variables to set when launching the MCP server. Names SHOULD be unique;
Agents MAY reject duplicates with `-32602`, and otherwise the last entry wins.
</ResponseField>
<ResponseField name="name" type={"string"} required>
Human-readable name identifying this MCP server.
Expand Down
2 changes: 1 addition & 1 deletion docs/protocol/v2/session-setup.mdx
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Expand Up @@ -533,7 +533,7 @@ Example stdio transport configuration:
}
```

Agents **SHOULD** launch stdio servers with the session's `cwd` as the working directory. `env` entries are added to the environment the Agent would otherwise give the process, replacing variables with the same name. Each `env` entry **MUST** have a unique `name`.
Agents **SHOULD** launch stdio servers with the session's `cwd` as the working directory. `env` entries are added to the environment the Agent would otherwise give the process, replacing variables with the same name. Each `env` entry **SHOULD** have a unique `name`. Agents **MAY** reject duplicates with `-32602`; otherwise the last entry with a given name wins.

#### HTTP Transport

Expand Down
2 changes: 1 addition & 1 deletion schema/v2/schema.json
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Expand Up @@ -6416,7 +6416,7 @@
"x-deserialize-default-on-null": true
},
"env": {
"description": "Environment variables to set when launching the MCP server.",
"description": "Environment variables to set when launching the MCP server. Names SHOULD be unique;\nAgents MAY reject duplicates with `-32602`, and otherwise the last entry wins.",
"type": "array",
"items": {
"$ref": "#/$defs/EnvVariable"
Expand Down
2 changes: 1 addition & 1 deletion schema/v2/schema.unstable.json
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Expand Up @@ -7578,7 +7578,7 @@
"x-deserialize-default-on-null": true
},
"env": {
"description": "Environment variables to set when launching the MCP server.",
"description": "Environment variables to set when launching the MCP server. Names SHOULD be unique;\nAgents MAY reject duplicates with `-32602`, and otherwise the last entry wins.",
"type": "array",
"items": {
"$ref": "#/$defs/EnvVariable"
Expand Down
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