# COMMENT ON CATALOG / SCHEMA: set the `description` of a catalog (`catalog` alone) or of one of its

`POST /datanotes/operations/comment_on/` (operation `comment_on`)

COMMENT ON CATALOG / SCHEMA: set the `description` of a catalog (`catalog` alone) or of one of its
schemas (`catalog` and `schema`) in metastore.yaml: what it holds, so agents pick the right place.
`description` "" removes it. An unknown catalog or schema is refused with the existing ones.
describe_database and `system.information_schema.catalogs` / `schemata` show it. Undo with
`undo_migration`. A table's description: alter_table.

The schema changes only through operations like this one: never edit metastore.yaml by hand (no validation, no undo).

## Parameters

| Name | In | Type | Required | Description |
| --- | --- | --- | --- | --- |
| `X-Datanotes-Actor` | header | `string` | no | JSON: on whose behalf the write is made, recorded in the journal (`harness`, `model`, `session`). |

## Request body

`application/json`, required

| Property | Type | Required | Default | Description |
| --- | --- | --- | --- | --- |
| `catalog` | `string` | yes |  |  |
| `schema` | `string \| null` | no | `null` | A schema of the catalog; omitted, the description is the catalog's. |
| `description` | `string` | yes |  | The new description; "" removes it. |
| `dry_run` | `boolean` | no | `false` |  |

## Responses

| Status | Description | Body |
| --- | --- | --- |
| 200 | Done. | `OpResult` (application/json) |
| 400 | Bad input: the body is not a JSON object, or an argument is unknown, missing or of the wrong type. | `Error` (application/json) |
| 401 | Missing or wrong bearer token. | `Error` (application/json) |
| 403 | A named token beyond its permissions (the engine's administration, tables outside its `write` patterns, schema changes without `ddl`). | `Error` (application/json) |
| 422 | Refused (validation failures, conflicts, an unmet `expect`): nothing written. Same body as 200, with `ok: false` and the reasons. | `OpResult` (application/json) |
| 500 | Unexpected error (`{error}`), or a write that failed partway and could not be rolled back: `rolled_back: false`, `failed` lists the files left (undo_migration on `migration_id` retries the rollback). | `OpResult \| Error` (application/json) |
| 503 | A write that failed partway (a file another program holds) and was rolled back: `rolled_back: true`, nothing written. Send it again later. Same body as 200, with `ok: false` and `failed`. | `OpResult` (application/json) |

The schemas named here are in [openapi.json](https://datanotes.dev/openapi.json) (`components.schemas`).