Add exec output-schema parameter (#4079)

Adds structured output to `exec` via the `--structured-output`
parameter.

codex-rs/core/src/chat_completions.rs

@@ -35,6 +35,12 @@ pub(crate) async fn stream_chat_completions(
     client: &reqwest::Client,
     provider: &ModelProviderInfo,
 ) -> Result<ResponseStream> {
+    if prompt.output_schema.is_some() {
+        return Err(CodexErr::UnsupportedOperation(
+            "output_schema is not supported for Chat Completions API".to_string(),
+        ));
+    }
+
     // Build messages array
     let mut messages = Vec::<serde_json::Value>::new();
 

codex-rs/core/src/client.rs

@@ -185,7 +185,7 @@ impl ModelClient {
 
         // Only include `text.verbosity` for GPT-5 family models
         let text = if self.config.model_family.family == "gpt-5" {
-            create_text_param_for_request(self.config.model_verbosity)
+            create_text_param_for_request(self.config.model_verbosity, &prompt.output_schema)
         } else {
             if self.config.model_verbosity.is_some() {
                 warn!(

codex-rs/core/src/client_common.rs

@@ -10,6 +10,7 @@ use codex_protocol::config_types::Verbosity as VerbosityConfig;
 use codex_protocol::models::ResponseItem;
 use futures::Stream;
 use serde::Serialize;
+use serde_json::Value;
 use std::borrow::Cow;
 use std::ops::Deref;
 use std::pin::Pin;
@@ -32,6 +33,9 @@ pub struct Prompt {
 
     /// Optional override for the built-in BASE_INSTRUCTIONS.
     pub base_instructions_override: Option<String>,
+
+    /// Optional the output schema for the model's response.
+    pub output_schema: Option<Value>,
 }
 
 impl Prompt {
@@ -90,14 +94,31 @@ pub(crate) struct Reasoning {
     pub(crate) summary: Option<ReasoningSummaryConfig>,
 }
 
+#[derive(Debug, Serialize, Default, Clone)]
+#[serde(rename_all = "snake_case")]
+pub(crate) enum TextFormatType {
+    #[default]
+    JsonSchema,
+}
+
+#[derive(Debug, Serialize, Default, Clone)]
+pub(crate) struct TextFormat {
+    pub(crate) r#type: TextFormatType,
+    pub(crate) strict: bool,
+    pub(crate) schema: Value,
+    pub(crate) name: String,
+}
+
 /// Controls under the `text` field in the Responses API for GPT-5.
-#[derive(Debug, Serialize, Default, Clone, Copy)]
+#[derive(Debug, Serialize, Default, Clone)]
 pub(crate) struct TextControls {
     #[serde(skip_serializing_if = "Option::is_none")]
     pub(crate) verbosity: Option<OpenAiVerbosity>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub(crate) format: Option<TextFormat>,
 }
 
-#[derive(Debug, Serialize, Default, Clone, Copy)]
+#[derive(Debug, Serialize, Default, Clone)]
 #[serde(rename_all = "lowercase")]
 pub(crate) enum OpenAiVerbosity {
     Low,
@@ -156,9 +177,20 @@ pub(crate) fn create_reasoning_param_for_request(
 
 pub(crate) fn create_text_param_for_request(
     verbosity: Option<VerbosityConfig>,
+    output_schema: &Option<Value>,
 ) -> Option<TextControls> {
-    verbosity.map(|v| TextControls {
+    if verbosity.is_none() && output_schema.is_none() {
-        verbosity: Some(v.into()),
+        return None;
+    }
+
+    Some(TextControls {
+        verbosity: verbosity.map(std::convert::Into::into),
+        format: output_schema.as_ref().map(|schema| TextFormat {
+            r#type: TextFormatType::JsonSchema,
+            strict: true,
+            schema: schema.clone(),
+            name: "codex_output_schema".to_string(),
+        }),
     })
 }
 
@@ -255,6 +287,7 @@ mod tests {
             prompt_cache_key: None,
             text: Some(TextControls {
                 verbosity: Some(OpenAiVerbosity::Low),
+                format: None,
             }),
         };
 
@@ -267,6 +300,52 @@ mod tests {
         );
     }
 
+    #[test]
+    fn serializes_text_schema_with_strict_format() {
+        let input: Vec<ResponseItem> = vec![];
+        let tools: Vec<serde_json::Value> = vec![];
+        let schema = serde_json::json!({
+            "type": "object",
+            "properties": {
+                "answer": {"type": "string"}
+            },
+            "required": ["answer"],
+        });
+        let text_controls =
+            create_text_param_for_request(None, &Some(schema.clone())).expect("text controls");
+
+        let req = ResponsesApiRequest {
+            model: "gpt-5",
+            instructions: "i",
+            input: &input,
+            tools: &tools,
+            tool_choice: "auto",
+            parallel_tool_calls: false,
+            reasoning: None,
+            store: false,
+            stream: true,
+            include: vec![],
+            prompt_cache_key: None,
+            text: Some(text_controls),
+        };
+
+        let v = serde_json::to_value(&req).expect("json");
+        let text = v.get("text").expect("text field");
+        assert!(text.get("verbosity").is_none());
+        let format = text.get("format").expect("format field");
+
+        assert_eq!(
+            format.get("name"),
+            Some(&serde_json::Value::String("codex_output_schema".into()))
+        );
+        assert_eq!(
+            format.get("type"),
+            Some(&serde_json::Value::String("json_schema".into()))
+        );
+        assert_eq!(format.get("strict"), Some(&serde_json::Value::Bool(true)));
+        assert_eq!(format.get("schema"), Some(&schema));
+    }
+
     #[test]
     fn omits_text_when_not_set() {
         let input: Vec<ResponseItem> = vec![];

codex-rs/core/src/codex.rs

@@ -31,6 +31,7 @@ use mcp_types::CallToolResult;
 use serde::Deserialize;
 use serde::Serialize;
 use serde_json;
+use serde_json::Value;
 use tokio::sync::Mutex;
 use tokio::sync::oneshot;
 use tokio::task::AbortHandle;
@@ -302,6 +303,7 @@ pub(crate) struct TurnContext {
     pub(crate) shell_environment_policy: ShellEnvironmentPolicy,
     pub(crate) tools_config: ToolsConfig,
     pub(crate) is_review_mode: bool,
+    pub(crate) final_output_json_schema: Option<Value>,
 }
 
 impl TurnContext {
@@ -469,6 +471,7 @@ impl Session {
             shell_environment_policy: config.shell_environment_policy.clone(),
             cwd,
             is_review_mode: false,
+            final_output_json_schema: None,
         };
         let sess = Arc::new(Session {
             conversation_id,
@@ -1237,6 +1240,7 @@ async fn submission_loop(
                     shell_environment_policy: prev.shell_environment_policy.clone(),
                     cwd: new_cwd.clone(),
                     is_review_mode: false,
+                    final_output_json_schema: None,
                 };
 
                 // Install the new persistent context for subsequent tasks/turns.
@@ -1271,6 +1275,7 @@ async fn submission_loop(
                 model,
                 effort,
                 summary,
+                final_output_json_schema,
             } => {
                 // attempt to inject input into current task
                 if let Err(items) = sess.inject_input(items).await {
@@ -1321,6 +1326,7 @@ async fn submission_loop(
                         shell_environment_policy: turn_context.shell_environment_policy.clone(),
                         cwd,
                         is_review_mode: false,
+                        final_output_json_schema,
                     };
 
                     // if the environment context has changed, record it in the conversation history
@@ -1575,6 +1581,7 @@ async fn spawn_review_thread(
         shell_environment_policy: parent_turn_context.shell_environment_policy.clone(),
         cwd: parent_turn_context.cwd.clone(),
         is_review_mode: true,
+        final_output_json_schema: None,
     };
 
     // Seed the child task with the review prompt as the initial user message.
@@ -1941,6 +1948,7 @@ async fn run_turn(
         input,
         tools,
         base_instructions_override: turn_context.base_instructions.clone(),
+        output_schema: turn_context.final_output_json_schema.clone(),
     };
 
     let mut retries = 0;
@@ -3604,6 +3612,7 @@ mod tests {
             shell_environment_policy: config.shell_environment_policy.clone(),
             tools_config,
             is_review_mode: false,
+            final_output_json_schema: None,
         };
         let session = Session {
             conversation_id,

codex-rs/core/src/codex/compact.rs

@@ -106,6 +106,7 @@ async fn run_compact_task_inner(
         input: turn_input,
         tools: Vec::new(),
         base_instructions_override: instructions_override,
+        output_schema: None,
     };
 
     let max_retries = turn_context.client.get_provider().stream_max_retries();

codex-rs/core/src/error.rs

@@ -104,6 +104,9 @@ pub enum CodexErr {
     #[error("codex-linux-sandbox was required but not provided")]
     LandlockSandboxExecutableNotProvided,
 
+    #[error("unsupported operation: {0}")]
+    UnsupportedOperation(String),
+
     // -----------------------------------------------------------------
     // Automatic conversions for common external error types
     // -----------------------------------------------------------------

codex-rs/core/tests/suite/json_result.rs

@@ -0,0 +1,97 @@
+#![cfg(not(target_os = "windows"))]
+
+use codex_core::protocol::AskForApproval;
+use codex_core::protocol::EventMsg;
+use codex_core::protocol::InputItem;
+use codex_core::protocol::Op;
+use codex_core::protocol::SandboxPolicy;
+use codex_protocol::config_types::ReasoningSummary;
+use core_test_support::non_sandbox_test;
+use core_test_support::responses;
+use core_test_support::test_codex::TestCodex;
+use core_test_support::test_codex::test_codex;
+use core_test_support::wait_for_event;
+use pretty_assertions::assert_eq;
+use responses::ev_assistant_message;
+use responses::ev_completed;
+use responses::sse;
+use responses::start_mock_server;
+
+const SCHEMA: &str = r#"
+{
+    "type": "object",
+    "properties": {
+        "explanation": { "type": "string" },
+        "final_answer": { "type": "string" }
+    },
+    "required": ["explanation", "final_answer"],
+    "additionalProperties": false
+}
+"#;
+
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn codex_returns_json_result() -> anyhow::Result<()> {
+    non_sandbox_test!(result);
+
+    let server = start_mock_server().await;
+
+    let sse1 = sse(vec![
+        ev_assistant_message(
+            "m2",
+            r#"{"explanation": "explanation", "final_answer": "final_answer"}"#,
+        ),
+        ev_completed("r1"),
+    ]);
+
+    let expected_schema: serde_json::Value = serde_json::from_str(SCHEMA)?;
+    let match_json_text_param = move |req: &wiremock::Request| {
+        let body: serde_json::Value = serde_json::from_slice(&req.body).unwrap_or_default();
+        let Some(text) = body.get("text") else {
+            return false;
+        };
+        let Some(format) = text.get("format") else {
+            return false;
+        };
+
+        format.get("name") == Some(&serde_json::Value::String("codex_output_schema".into()))
+            && format.get("type") == Some(&serde_json::Value::String("json_schema".into()))
+            && format.get("strict") == Some(&serde_json::Value::Bool(true))
+            && format.get("schema") == Some(&expected_schema)
+    };
+    responses::mount_sse_once(&server, match_json_text_param, sse1).await;
+
+    let TestCodex { codex, cwd, .. } = test_codex().build(&server).await?;
+
+    // 1) Normal user input – should hit server once.
+    codex
+        .submit(Op::UserTurn {
+            items: vec![InputItem::Text {
+                text: "hello world".into(),
+            }],
+            final_output_json_schema: Some(serde_json::from_str(SCHEMA)?),
+            cwd: cwd.path().to_path_buf(),
+            approval_policy: AskForApproval::Never,
+            sandbox_policy: SandboxPolicy::DangerFullAccess,
+            model: "gpt-5".to_string(),
+            effort: None,
+            summary: ReasoningSummary::Auto,
+        })
+        .await?;
+
+    let message = wait_for_event(&codex, |ev| matches!(ev, EventMsg::AgentMessage(_))).await;
+    if let EventMsg::AgentMessage(message) = message {
+        let json: serde_json::Value = serde_json::from_str(&message.message)?;
+        assert_eq!(
+            json.get("explanation"),
+            Some(&serde_json::Value::String("explanation".into()))
+        );
+        assert_eq!(
+            json.get("final_answer"),
+            Some(&serde_json::Value::String("final_answer".into()))
+        );
+    } else {
+        anyhow::bail!("expected agent message event");
+    }
+
+    Ok(())
+}

codex-rs/core/tests/suite/mod.rs

@@ -7,6 +7,7 @@ mod compact_resume_fork;
 mod exec;
 mod exec_stream_events;
 mod fork_conversation;
+mod json_result;
 mod live_cli;
 mod model_overrides;
 mod prompt_caching;

codex-rs/core/tests/suite/prompt_caching.rs

@@ -546,6 +546,7 @@ async fn per_turn_overrides_keep_cached_prefix_and_key_constant() {
             model: "o3".to_string(),
             effort: Some(ReasoningEffort::High),
             summary: ReasoningSummary::Detailed,
+            final_output_json_schema: None,
         })
         .await
         .unwrap();
@@ -655,6 +656,7 @@ async fn send_user_turn_with_no_changes_does_not_send_environment_context() {
             model: default_model.clone(),
             effort: default_effort,
             summary: default_summary,
+            final_output_json_schema: None,
         })
         .await
         .unwrap();
@@ -671,6 +673,7 @@ async fn send_user_turn_with_no_changes_does_not_send_environment_context() {
             model: default_model.clone(),
             effort: default_effort,
             summary: default_summary,
+            final_output_json_schema: None,
         })
         .await
         .unwrap();
@@ -766,6 +769,7 @@ async fn send_user_turn_with_changes_sends_environment_context() {
             model: default_model,
             effort: default_effort,
             summary: default_summary,
+            final_output_json_schema: None,
         })
         .await
         .unwrap();
@@ -782,6 +786,7 @@ async fn send_user_turn_with_changes_sends_environment_context() {
             model: "o3".to_string(),
             effort: Some(ReasoningEffort::High),
             summary: ReasoningSummary::Detailed,
+            final_output_json_schema: None,
         })
         .await
         .unwrap();

codex-rs/exec/src/cli.rs

@@ -52,6 +52,10 @@ pub struct Cli {
     #[arg(long = "skip-git-repo-check", default_value_t = false)]
     pub skip_git_repo_check: bool,
 
+    /// Path to a JSON Schema file describing the model's final response shape.
+    #[arg(long = "output-schema", value_name = "FILE")]
+    pub output_schema: Option<PathBuf>,
+
     #[clap(skip)]
     pub config_overrides: CliConfigOverrides,
 

codex-rs/exec/src/lib.rs

@@ -25,6 +25,7 @@ use codex_ollama::DEFAULT_OSS_MODEL;
 use codex_protocol::config_types::SandboxMode;
 use event_processor_with_human_output::EventProcessorWithHumanOutput;
 use event_processor_with_json_output::EventProcessorWithJsonOutput;
+use serde_json::Value;
 use tracing::debug;
 use tracing::error;
 use tracing::info;
@@ -51,6 +52,7 @@ pub async fn run_main(cli: Cli, codex_linux_sandbox_exe: Option<PathBuf>) -> any
         json: json_mode,
         sandbox_mode: sandbox_mode_cli_arg,
         prompt,
+        output_schema: output_schema_path,
         config_overrides,
     } = cli;
 
@@ -96,6 +98,8 @@ pub async fn run_main(cli: Cli, codex_linux_sandbox_exe: Option<PathBuf>) -> any
         }
     };
 
+    let output_schema = load_output_schema(output_schema_path);
+
     let (stdout_with_ansi, stderr_with_ansi) = match color {
         cli::Color::Always => (true, true),
         cli::Color::Never => (false, false),
@@ -193,7 +197,14 @@ pub async fn run_main(cli: Cli, codex_linux_sandbox_exe: Option<PathBuf>) -> any
     // is using.
     event_processor.print_config_summary(&config, &prompt);
 
-    if !skip_git_repo_check && get_git_repo_root(&config.cwd.to_path_buf()).is_none() {
+    let default_cwd = config.cwd.to_path_buf();
+    let default_approval_policy = config.approval_policy;
+    let default_sandbox_policy = config.sandbox_policy.clone();
+    let default_model = config.model.clone();
+    let default_effort = config.model_reasoning_effort;
+    let default_summary = config.model_reasoning_summary;
+
+    if !skip_git_repo_check && get_git_repo_root(&default_cwd).is_none() {
         eprintln!("Not inside a trusted directory and --skip-git-repo-check was not specified.");
         std::process::exit(1);
     }
@@ -288,7 +299,18 @@ pub async fn run_main(cli: Cli, codex_linux_sandbox_exe: Option<PathBuf>) -> any
 
     // Send the prompt.
     let items: Vec<InputItem> = vec![InputItem::Text { text: prompt }];
-    let initial_prompt_task_id = conversation.submit(Op::UserInput { items }).await?;
+    let initial_prompt_task_id = conversation
+        .submit(Op::UserTurn {
+            items,
+            cwd: default_cwd,
+            approval_policy: default_approval_policy,
+            sandbox_policy: default_sandbox_policy,
+            model: default_model,
+            effort: default_effort,
+            summary: default_summary,
+            final_output_json_schema: output_schema,
+        })
+        .await?;
     info!("Sent prompt with event ID: {initial_prompt_task_id}");
 
     // Run the loop until the task is complete.
@@ -327,3 +349,29 @@ async fn resolve_resume_path(
         Ok(None)
     }
 }
+
+fn load_output_schema(path: Option<PathBuf>) -> Option<Value> {
+    let path = path?;
+
+    let schema_str = match std::fs::read_to_string(&path) {
+        Ok(contents) => contents,
+        Err(err) => {
+            eprintln!(
+                "Failed to read output schema file {}: {err}",
+                path.display()
+            );
+            std::process::exit(1);
+        }
+    };
+
+    match serde_json::from_str::<Value>(&schema_str) {
+        Ok(value) => Some(value),
+        Err(err) => {
+            eprintln!(
+                "Output schema file {} is not valid JSON: {err}",
+                path.display()
+            );
+            std::process::exit(1);
+        }
+    }
+}

codex-rs/exec/tests/suite/mod.rs

@@ -1,5 +1,6 @@
 // Aggregates all former standalone integration tests as modules.
 mod apply_patch;
 mod common;
+mod output_schema;
 mod resume;
 mod sandbox;

codex-rs/exec/tests/suite/output_schema.rs

@@ -0,0 +1,76 @@
+#![cfg(not(target_os = "windows"))]
+#![allow(clippy::expect_used, clippy::unwrap_used)]
+
+use assert_cmd::prelude::*;
+use core_test_support::responses;
+use serde_json::Value;
+use std::process::Command;
+use tempfile::TempDir;
+use wiremock::matchers::any;
+
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn exec_includes_output_schema_in_request() -> anyhow::Result<()> {
+    let home = TempDir::new()?;
+    let workspace = TempDir::new()?;
+
+    let schema_contents = serde_json::json!({
+        "type": "object",
+        "properties": {
+            "answer": { "type": "string" }
+        },
+        "required": ["answer"],
+        "additionalProperties": false
+    });
+    let schema_path = workspace.path().join("schema.json");
+    std::fs::write(&schema_path, serde_json::to_vec_pretty(&schema_contents)?)?;
+    let expected_schema: Value = schema_contents;
+
+    let server = responses::start_mock_server().await;
+    let body = responses::sse(vec![
+        serde_json::json!({
+            "type": "response.created",
+            "response": {"id": "resp1"}
+        }),
+        responses::ev_assistant_message("m1", "fixture hello"),
+        responses::ev_completed("resp1"),
+    ]);
+    responses::mount_sse_once(&server, any(), body).await;
+
+    Command::cargo_bin("codex-exec")?
+        .current_dir(workspace.path())
+        .env("CODEX_HOME", home.path())
+        .env("OPENAI_API_KEY", "dummy")
+        .env("OPENAI_BASE_URL", format!("{}/v1", server.uri()))
+        .arg("--skip-git-repo-check")
+        .arg("-C")
+        .arg(workspace.path())
+        .arg("--output-schema")
+        .arg(&schema_path)
+        .arg("-m")
+        .arg("gpt-5")
+        .arg("tell me a joke")
+        .assert()
+        .success();
+
+    let requests = server
+        .received_requests()
+        .await
+        .expect("failed to capture requests");
+    assert_eq!(requests.len(), 1, "expected exactly one request");
+    let payload: Value = serde_json::from_slice(&requests[0].body)?;
+    let text = payload.get("text").expect("request missing text field");
+    let format = text
+        .get("format")
+        .expect("request missing text.format field");
+    assert_eq!(
+        format,
+        &serde_json::json!({
+            "name": "codex_output_schema",
+            "type": "json_schema",
+            "strict": true,
+            "schema": expected_schema,
+        })
+    );
+
+    Ok(())
+}

codex-rs/mcp-server/src/codex_message_processor.rs

@@ -1009,6 +1009,7 @@ impl CodexMessageProcessor {
                 model,
                 effort,
                 summary,
+                final_output_json_schema: None,
             })
             .await;
 

codex-rs/protocol/src/protocol.rs

@@ -24,6 +24,7 @@ use mcp_types::CallToolResult;
 use mcp_types::Tool as McpTool;
 use serde::Deserialize;
 use serde::Serialize;
+use serde_json::Value;
 use serde_with::serde_as;
 use strum_macros::Display;
 use ts_rs::TS;
@@ -87,6 +88,8 @@ pub enum Op {
 
         /// Will only be honored if the model is configured to use reasoning.
         summary: ReasoningSummaryConfig,
+        // The JSON schema to use for the final assistant message
+        final_output_json_schema: Option<Value>,
     },
 
     /// Override parts of the persistent turn context for subsequent turns.