> This page is for Developer Documentation.

> For clean Markdown of any page, append .md to the page URL.
> For a complete documentation index, see https://docs.benchling.com/llms.txt.
> For AI client integration (Claude Code, Cursor, etc.), connect to the MCP server at https://docs.benchling.com/_mcp/server.

# Get AaMonomer by ID

GET https://{tenant_name}.benchling.com/api/v3/aa-monomer/{aa_monomer_id}

Get a single AaMonomer by ID.

Reference: https://docs.benchling.com/docs/api/benchling-api/aa-monomer/get

## Authentication

- `Authorization` header (bearer token, required) — Bearer authentication of the form `Bearer <token>`, where token is your auth token.

## Request

### Path parameters

- `aa_monomer_id` (string, required) — ID of the AaMonomer.

### Query parameters

- `returning` (string, optional) — Comma-separated list of top-level fields to include in each returned item. Cannot overlap with omit.
- `omit` (string, optional) — Comma-separated list of top-level fields to omit from each returned item. Cannot overlap with returning.

### Headers

- `EARLY-ACCESS` (string, optional) — Set to true to access beta operations via /api/v3.

## Response

### 200

OK

- `__typename` (string, optional)
- `archiveReason` (string, optional, nullable)
- `archived` (boolean, optional)
- `attachmentPoints` (list of enum, optional) — The capping groups present at each attachment point where the monomer bonds to other monomers.
  - Allowed values: `H`, `OH`, `NH2`, `CH3`
- `calculatedMolecularWeight` (double, optional) — The molecular weight of the monomer with capping groups removed, computed using the average atomic weights of each element weighted by natural isotopic frequency.
- `canonicalSmiles` (string, optional) — The SMILES representation of the chemical structure after being standardized.
- `createdAt` (string, optional)
- `creator` (PrincipalRef, optional, nullable)
- `customMolecularWeight` (double, optional, nullable) — Optional molecular weight value that the user can provide to override the calculated value.
- `exactMolecularWeight` (double, optional) — The exact (monoisotopic) molecular weight of the monomer with capping groups removed, computed using the atomic weight of the most frequent isotope of each element.
- `id` (string, optional)
- `isNatural` (boolean, optional) — Whether this monomer represents a natural (unmodified) amino acid, as opposed to a modified or synthetic variant.
- `modifiedAt` (string, optional)
- `molfile` (string, optional) — The molfile representation of the chemical structure.
- `name` (string, optional)
- `naturalAnalog` (enum, optional) — The standard amino acid single-letter code that this monomer is an analog of.
  - Allowed values: `A`, `B`, `C`, `D`, `E`, `F`, `G`, `H`, `I`, `J`, `K`, `L`, `M`, `N`, `O`, `P`, `Q`, `R`, `S`, `T`, `U`, `V`, `W`, `X`, `Y`, `Z`
- `originalSmiles` (string, optional, nullable) — The SMILES string that was originally provided upon creation. Null if the user did not originally provide SMILES.
- `symbol` (string, optional) — User-defined identifier of the monomer, unique per tenant.

## Errors

### 400 Aa Monomer Get Request Bad Request Error

Bad Request

- `detail` (GeneralErrorDetail, required, nullable)
- `instance` (string, required)
- `status` (integer, required)
- `title` (string, required, nullable)
- `type` (string, required)
- `invalidId` (string, optional)

### 403 Aa Monomer Get Request Forbidden Error

Forbidden

- `detail` (GeneralErrorDetail, required, nullable)
- `instance` (string, required)
- `status` (integer, required)
- `title` (string, required, nullable)
- `type` (string, required)
- `invalidId` (string, optional)

### 404 Aa Monomer Get Request Not Found Error

Not Found

- `detail` (GeneralErrorDetail, required, nullable)
- `instance` (string, required)
- `status` (integer, required)
- `title` (string, required, nullable)
- `type` (string, required)
- `invalidId` (string, optional)

### 429 Aa Monomer Get Request Too Many Requests Error

Too Many Requests

- `detail` (TooManyRequestsErrorBodyDetail, required, nullable)
- `instance` (string, required)
- `status` (integer, required)
- `title` (string, required, nullable)
- `type` (string, required)
- `invalidId` (string, optional)

### 500 Aa Monomer Get Request Internal Server Error

Internal Server Error

- `detail` (InternalServerErrorBodyDetail, required, nullable)
- `instance` (string, required)
- `status` (integer, required)
- `title` (string, required, nullable)
- `type` (string, required)
- `errorId` (string, optional)

## Types

### PrincipalRef

- `__typename` (string, optional)
- `id` (string, optional)

### GeneralErrorDetail

### TooManyRequestsErrorBodyDetail

### InternalServerErrorBodyDetail

## Examples

**Response**

```json
{
  "__typename": "__typename",
  "archiveReason": "archiveReason",
  "archived": true,
  "attachmentPoints": [
    "H"
  ],
  "calculatedMolecularWeight": 1.1,
  "canonicalSmiles": "canonicalSmiles",
  "createdAt": "createdAt",
  "creator": {
    "__typename": "__typename",
    "id": "id"
  },
  "customMolecularWeight": 1.1,
  "exactMolecularWeight": 1.1,
  "id": "id",
  "isNatural": true,
  "modifiedAt": "modifiedAt",
  "molfile": "molfile",
  "name": "name",
  "naturalAnalog": "A",
  "originalSmiles": "originalSmiles",
  "symbol": "symbol"
}
```

**SDK Code**

```python
import requests

url = "https://{tenant_name}.benchling.com/api/v3/aa-monomer/aa_monomer_id"

headers = {"Authorization": "Bearer <token>"}

response = requests.get(url, headers=headers)

print(response.json())
```

```javascript
const url = 'https://{tenant_name}.benchling.com/api/v3/aa-monomer/aa_monomer_id';
const options = {method: 'GET', headers: {Authorization: 'Bearer <token>'}};

try {
  const response = await fetch(url, options);
  const data = await response.json();
  console.log(data);
} catch (error) {
  console.error(error);
}
```