---
title: "Create Log Entry"
method: POST
path: "/felix/synthesis-log"
tags: ["felix", "synthesis-log"]
---

# Create Log Entry

`POST /felix/synthesis-log`

Create a single synthesis log entry.

Args:
    request: Log entry data.
    auth: Authentication result.

Returns:
    The created SynthesisLogEntry.

Raises:
    HTTPException: If the entry could not be created.

## Request body

- SynthesisLogCreate — Request body for creating a single synthesis log entry.
  - `session_id` string, required — UUID grouping all entries for one synthesis session
  - `entry_type` 'prompt' | 'seed_generation' | 'seed_feedback' | 'prompt_update' | 'expansion' | 'finalization', required — Type of log entry
  - `content` object — Flexible payload keyed by entry_type
  - `dataset_id` string, nullable — Dataset ID, set when already linked
  - `project_id` string, nullable — Project ID for the session

## Response `200`

Successful Response

- SynthesisLogEntry — Single synthesis log entry returned from the API.
  - `id` string, required
  - `user_id` string, required
  - `dataset_id` string, nullable
  - `project_id` string, nullable
  - `session_id` string, required
  - `entry_type` 'prompt' | 'seed_generation' | 'seed_feedback' | 'prompt_update' | 'expansion' | 'finalization', required
  - `content` object, required
  - `created_at` string, date-time, required

## Other responses

- `422` — Validation Error

## Changes

- **2026-09-24** `1cffaad2a921` — 1 warning, 1 info
  - removed the optional property `detail` from the response with the `422` status
  - added the required property `error` to the response with the `422` status

[Change history](https://skmtc.dev/pioneer/apis/brain-api/changes/felix/synthesis-log/post.md)

---

[API](https://skmtc.dev/pioneer/apis/brain-api.md) · [All operations](https://skmtc.dev/pioneer/apis/brain-api/llms.txt) · [OpenAPI document](https://skmtc.dev/pioneer/apis/brain-api/revisions/1cffaad2a921?raw)