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codex-tools: extract MCP schema adapters (#15928)

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## Why

`codex-tools` already owns the shared tool input schema model and parser
from the first extraction step, but `core/src/tools/spec.rs` still owned
the MCP-specific adapter that normalizes `rmcp::model::Tool` schemas and
wraps `structuredContent` into the call result output schema.

Keeping that adapter in `codex-core` means the reusable MCP schema path
is still split across crates, and the unit tests for that logic stay
anchored in `codex-core` even though the runtime orchestration does not
need to move yet.

This change takes the next small step by moving the reusable MCP schema
adapter into `codex-tools` while leaving `ResponsesApiTool` assembly in
`codex-core`.

## What changed

- added `tools/src/mcp_tool.rs` and sibling
`tools/src/mcp_tool_tests.rs`
- introduced `ParsedMcpTool`, `parse_mcp_tool()`, and
`mcp_call_tool_result_output_schema()` in `codex-tools`
- updated `core/src/tools/spec.rs` to consume parsed MCP tool parts from
`codex-tools`
- removed the now-redundant MCP schema unit tests from
`core/src/tools/spec_tests.rs`
- expanded `codex-rs/tools/README.md` to describe this second migration
step

## Test plan

- `cargo test -p codex-tools`
- `cargo test -p codex-core --lib tools::spec::`
This commit is contained in:
Michael Bolin
2026-03-26 19:57:26 -07:00
committed by GitHub
parent d838c23867
commit be5afc65d3
8 changed files with 212 additions and 197 deletions
Download Patch File Download Diff File Expand all files Collapse all files

1
codex-rs/Cargo.lock generated
View File

@@ -2633,6 +2633,7 @@ name = "codex-tools"
version = "0.0.0"
dependencies = [
"pretty_assertions",
"rmcp",
"serde",
"serde_json",
]

73
codex-rs/core/src/tools/spec.rs
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@@ -46,6 +46,7 @@ use codex_protocol::openai_models::WebSearchToolType;
use codex_protocol::protocol::SandboxPolicy;
use codex_protocol::protocol::SessionSource;
use codex_protocol::protocol::SubAgentSource;
use codex_tools::parse_mcp_tool;
pub use codex_tools::parse_tool_input_schema;
use codex_utils_absolute_path::AbsolutePathBuf;
use serde::Deserialize;
@@ -58,6 +59,9 @@ use std::path::PathBuf;
pub type JsonSchema = codex_tools::JsonSchema;
#[cfg(test)]
pub(crate) use codex_tools::mcp_call_tool_result_output_schema;
const TOOL_SEARCH_DESCRIPTION_TEMPLATE: &str =
include_str!("../../templates/search_tool/tool_description.md");
const TOOL_SUGGEST_DESCRIPTION_TEMPLATE: &str =
@@ -2362,15 +2366,15 @@ pub(crate) fn mcp_tool_to_openai_tool(
fully_qualified_name: String,
tool: rmcp::model::Tool,
) -> Result<ResponsesApiTool, serde_json::Error> {
let (description, input_schema, output_schema) = mcp_tool_to_openai_tool_parts(tool)?;
let parsed_tool = parse_mcp_tool(&tool)?;
Ok(ResponsesApiTool {
name: fully_qualified_name,
description,
description: parsed_tool.description,
strict: false,
defer_loading: None,
parameters: input_schema,
output_schema,
parameters: parsed_tool.input_schema,
output_schema: Some(parsed_tool.output_schema),
})
}
@@ -2378,14 +2382,14 @@ pub(crate) fn mcp_tool_to_deferred_openai_tool(
name: String,
tool: rmcp::model::Tool,
) -> Result<ResponsesApiTool, serde_json::Error> {
let (description, input_schema, _) = mcp_tool_to_openai_tool_parts(tool)?;
let parsed_tool = parse_mcp_tool(&tool)?;
Ok(ResponsesApiTool {
name,
description,
description: parsed_tool.description,
strict: false,
defer_loading: Some(true),
parameters: input_schema,
parameters: parsed_tool.input_schema,
output_schema: None,
})
}
@@ -2405,61 +2409,6 @@ fn dynamic_tool_to_openai_tool(
})
}
fn mcp_tool_to_openai_tool_parts(
tool: rmcp::model::Tool,
) -> Result<(String, JsonSchema, Option<JsonValue>), serde_json::Error> {
let rmcp::model::Tool {
description,
input_schema,
output_schema,
..
} = tool;
let mut serialized_input_schema = serde_json::Value::Object(input_schema.as_ref().clone());
// OpenAI models mandate the "properties" field in the schema. Some MCP
// servers omit it (or set it to null), so we insert an empty object to
// match the behavior of the Agents SDK.
if let serde_json::Value::Object(obj) = &mut serialized_input_schema
&& obj.get("properties").is_none_or(serde_json::Value::is_null)
{
obj.insert(
"properties".to_string(),
serde_json::Value::Object(serde_json::Map::new()),
);
}
let input_schema = parse_tool_input_schema(&serialized_input_schema)?;
let structured_content_schema = output_schema
.map(|output_schema| serde_json::Value::Object(output_schema.as_ref().clone()))
.unwrap_or_else(|| JsonValue::Object(serde_json::Map::new()));
let output_schema = Some(mcp_call_tool_result_output_schema(
structured_content_schema,
));
let description = description.map(Into::into).unwrap_or_default();
Ok((description, input_schema, output_schema))
}
fn mcp_call_tool_result_output_schema(structured_content_schema: JsonValue) -> JsonValue {
json!({
"type": "object",
"properties": {
"content": {
"type": "array",
"items": {}
},
"structuredContent": structured_content_schema,
"isError": {
"type": "boolean"
},
"_meta": {}
},
"required": ["content"],
"additionalProperties": false
})
}
/// Builds the tool registry builder while collecting tool specs for later serialization.
#[cfg(test)]
pub(crate) fn build_specs(

133
codex-rs/core/src/tools/spec_tests.rs
View File

@@ -63,139 +63,6 @@ fn search_capable_model_info() -> ModelInfo {
model_info
}
#[test]
fn mcp_tool_to_openai_tool_inserts_empty_properties() {
let mut schema = rmcp::model::JsonObject::new();
schema.insert("type".to_string(), serde_json::json!("object"));
let tool = rmcp::model::Tool {
name: "no_props".to_string().into(),
title: None,
description: Some("No properties".to_string().into()),
input_schema: std::sync::Arc::new(schema),
output_schema: None,
annotations: None,
execution: None,
icons: None,
meta: None,
};
let openai_tool =
mcp_tool_to_openai_tool("server/no_props".to_string(), tool).expect("convert tool");
let parameters = serde_json::to_value(openai_tool.parameters).expect("serialize schema");
assert_eq!(parameters.get("properties"), Some(&serde_json::json!({})));
}
#[test]
fn mcp_tool_to_openai_tool_preserves_top_level_output_schema() {
let mut input_schema = rmcp::model::JsonObject::new();
input_schema.insert("type".to_string(), serde_json::json!("object"));
let mut output_schema = rmcp::model::JsonObject::new();
output_schema.insert(
"properties".to_string(),
serde_json::json!({
"result": {
"properties": {
"nested": {}
}
}
}),
);
output_schema.insert("required".to_string(), serde_json::json!(["result"]));
let tool = rmcp::model::Tool {
name: "with_output".to_string().into(),
title: None,
description: Some("Has output schema".to_string().into()),
input_schema: std::sync::Arc::new(input_schema),
output_schema: Some(std::sync::Arc::new(output_schema)),
annotations: None,
execution: None,
icons: None,
meta: None,
};
let openai_tool = mcp_tool_to_openai_tool("mcp__server__with_output".to_string(), tool)
.expect("convert tool");
assert_eq!(
openai_tool.output_schema,
Some(serde_json::json!({
"type": "object",
"properties": {
"content": {
"type": "array",
"items": {}
},
"structuredContent": {
"properties": {
"result": {
"properties": {
"nested": {}
}
}
},
"required": ["result"]
},
"isError": {
"type": "boolean"
},
"_meta": {}
},
"required": ["content"],
"additionalProperties": false
}))
);
}
#[test]
fn mcp_tool_to_openai_tool_preserves_output_schema_without_inferred_type() {
let mut input_schema = rmcp::model::JsonObject::new();
input_schema.insert("type".to_string(), serde_json::json!("object"));
let mut output_schema = rmcp::model::JsonObject::new();
output_schema.insert("enum".to_string(), serde_json::json!(["ok", "error"]));
let tool = rmcp::model::Tool {
name: "with_enum_output".to_string().into(),
title: None,
description: Some("Has enum output schema".to_string().into()),
input_schema: std::sync::Arc::new(input_schema),
output_schema: Some(std::sync::Arc::new(output_schema)),
annotations: None,
execution: None,
icons: None,
meta: None,
};
let openai_tool = mcp_tool_to_openai_tool("mcp__server__with_enum_output".to_string(), tool)
.expect("convert tool");
assert_eq!(
openai_tool.output_schema,
Some(serde_json::json!({
"type": "object",
"properties": {
"content": {
"type": "array",
"items": {}
},
"structuredContent": {
"enum": ["ok", "error"]
},
"isError": {
"type": "boolean"
},
"_meta": {}
},
"required": ["content"],
"additionalProperties": false
}))
);
}
#[test]
fn search_tool_deferred_tools_always_set_defer_loading_true() {
let tool = mcp_tool(

6
codex-rs/tools/Cargo.toml
View File

@@ -8,6 +8,12 @@ version.workspace = true
workspace = true
[dependencies]
rmcp = { workspace = true, default-features = false, features = [
"base64",
"macros",
"schemars",
"server",
] }
serde = { workspace = true, features = ["derive"] }
serde_json = { workspace = true }

7
codex-rs/tools/README.md
View File

@@ -4,12 +4,15 @@
shared across multiple crates and does not need to stay coupled to
`codex-core`.
Today this crate is intentionally small. It only owns the shared tool input
schema model and parser that were previously defined in `core/src/tools/spec.rs`:
Today this crate is intentionally small. It currently owns the shared tool
schema primitives that no longer need to live in `core/src/tools/spec.rs`:
- `JsonSchema`
- `AdditionalProperties`
- `parse_tool_input_schema()`
- `ParsedMcpTool`
- `parse_mcp_tool()`
- `mcp_call_tool_result_output_schema()`
That extraction is the first step in a longer migration. The goal is not to
move all of `core/src/tools` into this crate in one shot. Instead, the plan is

4
codex-rs/tools/src/lib.rs
View File

@@ -1,7 +1,11 @@
//! Shared tool-schema parsing primitives that can live outside `codex-core`.
mod json_schema;
mod mcp_tool;
pub use json_schema::AdditionalProperties;
pub use json_schema::JsonSchema;
pub use json_schema::parse_tool_input_schema;
pub use mcp_tool::ParsedMcpTool;
pub use mcp_tool::mcp_call_tool_result_output_schema;
pub use mcp_tool::parse_mcp_tool;

65
codex-rs/tools/src/mcp_tool.rs Normal file
View File

@@ -0,0 +1,65 @@
use crate::JsonSchema;
use crate::parse_tool_input_schema;
use serde_json::Value as JsonValue;
use serde_json::json;
/// Parsed MCP tool metadata and schemas that can be adapted into a higher-level
/// tool spec by downstream crates.
#[derive(Debug, PartialEq)]
pub struct ParsedMcpTool {
pub description: String,
pub input_schema: JsonSchema,
pub output_schema: JsonValue,
}
pub fn parse_mcp_tool(tool: &rmcp::model::Tool) -> Result<ParsedMcpTool, serde_json::Error> {
let mut serialized_input_schema = serde_json::Value::Object(tool.input_schema.as_ref().clone());
// OpenAI models mandate the "properties" field in the schema. Some MCP
// servers omit it (or set it to null), so we insert an empty object to
// match the behavior of the Agents SDK.
if let serde_json::Value::Object(obj) = &mut serialized_input_schema
&& obj.get("properties").is_none_or(serde_json::Value::is_null)
{
obj.insert(
"properties".to_string(),
serde_json::Value::Object(serde_json::Map::new()),
);
}
let input_schema = parse_tool_input_schema(&serialized_input_schema)?;
let structured_content_schema = tool
.output_schema
.as_ref()
.map(|output_schema| serde_json::Value::Object(output_schema.as_ref().clone()))
.unwrap_or_else(|| JsonValue::Object(serde_json::Map::new()));
Ok(ParsedMcpTool {
description: tool.description.clone().map(Into::into).unwrap_or_default(),
input_schema,
output_schema: mcp_call_tool_result_output_schema(structured_content_schema),
})
}
pub fn mcp_call_tool_result_output_schema(structured_content_schema: JsonValue) -> JsonValue {
json!({
"type": "object",
"properties": {
"content": {
"type": "array",
"items": {}
},
"structuredContent": structured_content_schema,
"isError": {
"type": "boolean"
},
"_meta": {}
},
"required": ["content"],
"additionalProperties": false
})
}
#[cfg(test)]
#[path = "mcp_tool_tests.rs"]
mod tests;

120
codex-rs/tools/src/mcp_tool_tests.rs Normal file
View File

@@ -0,0 +1,120 @@
use super::ParsedMcpTool;
use super::mcp_call_tool_result_output_schema;
use super::parse_mcp_tool;
use crate::JsonSchema;
use pretty_assertions::assert_eq;
use std::collections::BTreeMap;
fn mcp_tool(name: &str, description: &str, input_schema: serde_json::Value) -> rmcp::model::Tool {
rmcp::model::Tool {
name: name.to_string().into(),
title: None,
description: Some(description.to_string().into()),
input_schema: std::sync::Arc::new(rmcp::model::object(input_schema)),
output_schema: None,
annotations: None,
execution: None,
icons: None,
meta: None,
}
}
#[test]
fn parse_mcp_tool_inserts_empty_properties() {
let tool = mcp_tool(
"no_props",
"No properties",
serde_json::json!({
"type": "object"
}),
);
assert_eq!(
parse_mcp_tool(&tool).expect("parse MCP tool"),
ParsedMcpTool {
description: "No properties".to_string(),
input_schema: JsonSchema::Object {
properties: BTreeMap::new(),
required: None,
additional_properties: None,
},
output_schema: mcp_call_tool_result_output_schema(serde_json::json!({})),
}
);
}
#[test]
fn parse_mcp_tool_preserves_top_level_output_schema() {
let mut tool = mcp_tool(
"with_output",
"Has output schema",
serde_json::json!({
"type": "object"
}),
);
tool.output_schema = Some(std::sync::Arc::new(rmcp::model::object(
serde_json::json!({
"properties": {
"result": {
"properties": {
"nested": {}
}
}
},
"required": ["result"]
}),
)));
assert_eq!(
parse_mcp_tool(&tool).expect("parse MCP tool"),
ParsedMcpTool {
description: "Has output schema".to_string(),
input_schema: JsonSchema::Object {
properties: BTreeMap::new(),
required: None,
additional_properties: None,
},
output_schema: mcp_call_tool_result_output_schema(serde_json::json!({
"properties": {
"result": {
"properties": {
"nested": {}
}
}
},
"required": ["result"]
})),
}
);
}
#[test]
fn parse_mcp_tool_preserves_output_schema_without_inferred_type() {
let mut tool = mcp_tool(
"with_enum_output",
"Has enum output schema",
serde_json::json!({
"type": "object"
}),
);
tool.output_schema = Some(std::sync::Arc::new(rmcp::model::object(
serde_json::json!({
"enum": ["ok", "error"]
}),
)));
assert_eq!(
parse_mcp_tool(&tool).expect("parse MCP tool"),
ParsedMcpTool {
description: "Has enum output schema".to_string(),
input_schema: JsonSchema::Object {
properties: BTreeMap::new(),
required: None,
additional_properties: None,
},
output_schema: mcp_call_tool_result_output_schema(serde_json::json!({
"enum": ["ok", "error"]
})),
}
);
}