# substack.post_comments

**stable** **Advanced**

Comments on a Substack post (by post id).

`GET /v1/substack/post_comments`

## What you get

A list of Substack results in Onekey's unified shape, in `data` (an array). An empty array is a normal, successful answer and is charged like any other; a source that reports "nothing found" as an error returns a free `404 not_found` instead.

## What it costs

- **Advanced · 5 credits** for a fresh fetch, charged only when it succeeds.
- **Free when served from cache (0.2 credit for a cached response over 100 KB).**
- **Free** if the request is invalid (never charged) or the source fails or reports not found (refunded).

## Parameters

| Name | Type | Required | Default | What it is | Constraints |
| --- | --- | --- | --- | --- | --- |
| `pub` | string | yes | (required) | Allowlisted Substack publication host, e.g. www.astralcodexten.com | max 253 chars; must match `[a-z0-9.-]{3,253}`; trimmed, lowercased |
| `id` | string | yes | (required) | Numeric post id | max 12 chars; must match `[0-9]{3,12}`; trimmed |

## Request

```bash
curl "https://api.onekey.dev/v1/substack/post_comments?pub=www.astralcodexten.com&id=217850009" \
  -H "x-api-key: YOUR_API_KEY"
```

```python
import requests

res = requests.get(
    "https://api.onekey.dev/v1/substack/post_comments",
    params={"pub": "www.astralcodexten.com", "id": "217850009"},
    headers={"x-api-key": "YOUR_API_KEY"},
)
body = res.json()

if body["success"]:
    print(body["data"])
else:
    print(body["error"]["code"], body["error"]["message"])
```

```javascript
const params = new URLSearchParams({ pub: "www.astralcodexten.com", id: "217850009" });
const res = await fetch(`https://api.onekey.dev/v1/substack/post_comments?${params}`, {
  headers: { "x-api-key": "YOUR_API_KEY" },
});
const body = await res.json();

if (body.success) console.log(body.data);
else console.error(body.error.code, body.error.message);
```

## Recorded response

A real Substack response, recorded and returned in Onekey's shape. Fields the platform does not provide are `null`.

```json
{
  "success": true,
  "data": [
    {
      "content": {
        "id": "348018753",
        "text": "A while back Nat Friedman's PlasticList (plasticlist.org) tested hundreds of foods for phthalates and bisphenols (BPA and relatives). I built www.laboratory.love to make that kind of data easier to browse, and to fund new tests. It now has browsable results for about 250 products, PlasticList's data plus products commissioned directly on laboratory.love. Pushed a big redesign last week: - You can now search or browse by category (water, baby food, fast food, supplements…). Every product is rated as a share of the tolerable daily intake per serving, and you can switch between child and adult body weight. - Untested products. If search finds nothing, you can chip in from $10 to quickly spin up a crowdfund page for that product. Once a product reaches its goal, we buy three samples and publish the results. Contributions are refunded after 365 days if it isn't funded. - We also have on-demand testing if you want a specific product tested now!",
        "createdAt": "2026-09-28T17:46:15Z"
      },
      "author": {
        "displayName": "Collin",
        "id": "2152739",
        "avatarUrl": "https://substack-post-media.s3.amazonaws.com/public/images/9af096a2-544e-4a9c-942a-f71a91c3be1d_958x958.png"
      },
      "engagement": {
        "likes": 1
      }
    },
    {
      "content": {
        "id": "348000586",
        "text": "I recently learned that the fruit fly brain is fully digitally mapped and open source. Isn't this really bad? Should we be generating billions of wire-headed flies? Maybe I mis understand what this digital mapping actually entails.",
        "createdAt": "2026-09-28T17:23:24Z"
      },
      "author": {
        "displayName": "Bean Sprugget (bean)",
        "id": "10764977",
        "avatarUrl": "https://substack-post-media.s3.amazonaws.com/public/images/751e0170-af56-452b-8c56-7be991de3806_96x96.png"
      },
      "engagement": {
        "likes": 1
      }
    }
  ],
  "metadata": {
    "platform": "substack",
    "endpoint": "post_comments",
    "cached": false,
    "stale": false,
    "age_s": 0,
    "fetched_at": "2026-01-01T12:00:00+00:00",
    "credits_charged": 5,
    "request_id": "7f3a9c2e5b1d4c8fa2e6d0b9c4f18e37"
  },
  "error": null
}
```

## Field mapping

How this endpoint's source fields become Onekey's [unified schema](https://onekey.dev/docs/schema.md). Fields the source lacks come back as `null`.

| Source path | Onekey field | Transform |
| --- | --- | --- |
| `id` | `content.id` | `toString` |
| `body` | `content.text` | `stripHtml` |
| `name` | `author.displayName` | - |
| `user_id` | `author.id` | `toString` |
| `date` | `content.createdAt` | `toIsoDate` |
| `reaction_count` | `engagement.likes` | `toNumber` |
| `photo_url` | `author.avatarUrl` | `safeUrl` |

## Caching and freshness

- Fresh for about 2 minutes. Repeat calls in that window are served from cache and are free.
- Between 2 minutes and 15 minutes the cached copy is still served instantly and marked `stale: true` while Onekey refreshes it in the background.
- If the source is down when a refresh is needed, the last copy can be served for up to 1 hour more (marked stale).
- A "not found" is remembered for 1 minute and is free.
- The cache is shared across all customers, which is what keeps repeat calls cheap.

## What can go wrong

| Status | Code | What to do |
| --- | --- | --- |
| 401 | `unauthorized` | Check the `x-api-key` header. |
| 402 | `insufficient_credits` | [Add credits](https://onekey.dev/pricing); your balance must cover the price. |
| 404 | `not_found` | Unknown endpoint path. |
| 422 | `invalid_params` | Fix the parameters using the table above. Free. |
| 429 | `rate_limited` | Wait `Retry-After` seconds, then retry. |
| 502 | `upstream_error` | The source failed. Refunded; retry with backoff. |

See [Errors](https://onekey.dev/docs/errors.md) for the full list and retry guidance.

Status: stable (verified against the live source).