# CSV fill defaults

`csv-fill-defaults` · version 1.0.0 · CSV & tables · free, no key needed

Replace empty cells in named CSV columns with exact default strings.

**Use when you need to: csv fill defaults · fill empty csv cells with defaults · replace empty csv cells.**

## Supported

- csv fill defaults
- fill empty csv cells with defaults
- replace empty csv cells
- csv fill empty columns

## Not supported

- trim cells before filling
- fill whitespace-only cells
- infer defaults
- fuzzy column matching
- type coercion
- read files
- fetch urls

## Behavior

- The first CSV record is the header row.
- defaults own keys must name existing headers exactly; unknown columns are rejected.
- Only cells whose string length is 0 are replaced; whitespace-only cells are left unchanged.
- An empty default string is a no-op and does not increment cells_filled.
- Other columns and non-empty cells are preserved without trimming or type coercion.
- An empty document without a header is rejected when defaults is non-empty; a header-only document yields header-only output.
- The first output header name may not begin with U+FEFF because it is ambiguous with a CSV byte-order mark.

## Input

- `csv` (string, required): max length 256000
- `defaults` (object, required)

## Output

- `csv` (string, required)
- `cells_filled` (integer, required): min 0

## Limits

- max input bytes: 256000
- max data rows: 5000
- max columns: 256
- max header name bytes: 256
- max default columns: 256
- max output bytes: 256000

## Example

Request input:

```json
{
  "csv": "name,city,status\nAda,,\n,London,ok\n",
  "defaults": {
    "name": "Anonymous",
    "city": "Unknown",
    "status": "pending"
  }
}
```

Response:

```json
{
  "result": {
    "csv": "name,city,status\nAda,Unknown,pending\nAnonymous,London,ok\n",
    "cells_filled": 3
  }
}
```

## How to call it

### MCP

Connect `https://computefirst.net/mcp` ([setup](/docs#connect)), then call `execute` with:

```json
{
  "id": "csv-fill-defaults",
  "version": "1.0.0",
  "input": {
    "csv": "name,city,status\nAda,,\n,London,ok\n",
    "defaults": {
      "name": "Anonymous",
      "city": "Unknown",
      "status": "pending"
    }
  }
}
```

### HTTP (no key)

```sh
curl -X POST https://computefirst.net/v1/tools/csv-fill-defaults/versions/1.0.0/execute \
  -H "Content-Type: application/json" \
  -d '{"csv":"name,city,status\nAda,,\n,London,ok\n","defaults":{"name":"Anonymous","city":"Unknown","status":"pending"}}'
```

The machine-readable contract is at [/v1/tools/csv-fill-defaults/versions/1.0.0](/v1/tools/csv-fill-defaults/versions/1.0.0).

### CLI

```sh
node cli.mjs run csv-fill-defaults 1.0.0 --input input.json --base-url https://computefirst.net
```

Get the client at [/clients/cli/](/clients/cli/).

## Related tools

- [CSV filter empty](/tools/csv-filter-empty): Keep or drop CSV rows whose named column is the empty string.
- [CSV merge columns](/tools/csv-merge-columns): Join named CSV columns with an exact separator into one column.
- [CSV replace exact](/tools/csv-replace-exact): Replace CSV data cells whose entire value equals an exact find string.
- [CSV concat](/tools/csv-concat): Concatenate CSV documents that share identical headers, preserving document and row order.
- [CSV dedupe](/tools/csv-dedupe): Remove duplicate CSV data rows while preserving the first occurrence.
- [CSV drop columns](/tools/csv-drop-columns): Drop named CSV columns and keep the remaining columns in original header order.