# Merge CSV

- Human page: https://happytails.ai/en/spreadsheet-tools/merge-csv/
- Markdown: https://happytails.ai/en/spreadsheet-tools/merge-csv.md
- Structured JSON: https://happytails.ai/agents/en/spreadsheet-tools/merge-csv/index.json
- Visibility: public

## Tool capabilities

| Property | Value |
| --- | --- |
| Tool ID | `merge-csv` |
| Category | spreadsheet-tools |
| Implementation | Registered implementation. Registration alone is not a production-quality guarantee. |
| Browser execution | Use the visible action or interactive controls. |
| Browser processing | Browser; see tool notes for network behavior. |
| HTTP API | /api/v1/tools/merge-csv/run |
| Browser-agent interface | run_current_tool |

### Inputs and settings

No free-text input is required. Use the file inputs and/or settings below.

Accepted browser files: `See implementation notes`. Multiple files are supported.

| Setting | Meaning | Control type | Default | Constraints |
| --- | --- | --- | --- | --- |
| `delimiter` | CSV separator | select | "," | Allowed: ,, ;, 	 |

### HTTP contract

API calls process supplied data on the server. The website origin is `https://happytails.ai`. Server API hosting is not connected on the public website yet. Use your local server origin to test these requests.

```http
POST https://happytails.ai/api/v1/tools/merge-csv/run
Content-Type: application/json
```

[Detailed operation reference](https://happytails.ai/en/api/tools/merge-csv.md) · [Shared API guide](https://happytails.ai/en/api.md)

#### Limits

| Limit | Value |
| --- | --- |
| request_bytes | 8388608 |
| input_characters | 1000000 |
| files_bytes | 5242880 |
| max_files | 20 |
| timeout_seconds | 12 |

#### Complete input schema

```json
{
  "type": "object",
  "additionalProperties": false,
  "properties": {
    "input": {
      "type": "string",
      "maxLength": 1000000,
      "default": "",
      "description": "Plain text input. File tools use files instead unless otherwise documented."
    },
    "options": {
      "type": "object",
      "additionalProperties": false,
      "properties": {
        "delimiter": {
          "type": "string",
          "description": "CSV separator",
          "default": ",",
          "enum": [
            ",",
            ";",
            "\t"
          ]
        }
      }
    },
    "files": {
      "type": "array",
      "maxItems": 20,
      "items": {
        "type": "object",
        "required": [
          "name",
          "base64"
        ],
        "additionalProperties": false,
        "properties": {
          "name": {
            "type": "string",
            "maxLength": 200,
            "description": "Filename only, no path."
          },
          "mime": {
            "type": "string",
            "maxLength": 150
          },
          "bytes": {
            "type": "integer",
            "minimum": 0,
            "description": "Optional decoded byte count; must match content if supplied."
          },
          "base64": {
            "type": "string",
            "contentEncoding": "base64",
            "description": "File bytes as padded base64. Use the tool-specific limits.files_bytes value for the total decoded input size."
          }
        }
      }
    }
  }
}
```

#### Complete output schema

```json
{
  "type": "object",
  "required": [
    "tool",
    "result"
  ],
  "properties": {
    "tool": {
      "type": "string"
    },
    "result": {
      "type": "object",
      "required": [
        "text",
        "files"
      ],
      "properties": {
        "text": {
          "type": [
            "string",
            "null"
          ]
        },
        "data": {
          "description": "Parsed JSON when the textual result is JSON."
        },
        "name": {
          "type": "string"
        },
        "mime": {
          "type": "string"
        },
        "files": {
          "type": "array",
          "items": {
            "type": "object",
            "required": [
              "name",
              "mime",
              "bytes",
              "base64"
            ],
            "properties": {
              "name": {
                "type": "string"
              },
              "mime": {
                "type": "string"
              },
              "bytes": {
                "type": "integer"
              },
              "base64": {
                "type": "string",
                "contentEncoding": "base64"
              }
            }
          }
        }
      }
    }
  }
}
```

#### Error and retry handling

Failures return a non-200 status and `error.code` plus `error.message`. Correct invalid input before retrying; retry server-busy responses with bounded backoff. Returned files contain Base64 data, not persistent download URLs. Decode and inspect the output before treating conversion as successful. See the shared API guide for the complete status and timeout rules.

### Browser-agent workflow

1. Open the human page in a browser that supports WebMCP.
2. Discover the interface exposed by that page; use its actual schema.
3. Select files on the page first when the tool requires files.
4. Call `run_current_tool` with valid input and settings.
5. Inspect the returned result or error and the displayed output. Retrieve files from the displayed download links.

Calls do not automatically copy or download results. Browser permissions still apply. Interface availability alone is not proof of successful execution.

### Planning specification

Append with header alignment; preserve types; source-file column option.

This describes intended requirements. Use the implementation notes, interface schema and observed output to determine current support.

### Complete machine-readable capability record

```json
{
  "id": "merge-csv",
  "category": "spreadsheet-tools",
  "built": true,
  "requirements": "Append with header alignment; preserve types; source-file column option.",
  "implementation": {
    "fields": [
      {
        "key": "delimiter",
        "label": "CSV separator",
        "value": ",",
        "type": "select",
        "values": [
          ",",
          ";",
          "\t"
        ]
      }
    ],
    "files": true,
    "multiple": true,
    "input": false,
    "experience": {
      "automatic": false,
      "single": false,
      "label": "Your text",
      "placeholder": "Type or paste your input…",
      "help": "Up to 1,000,000 characters. Review the settings before running.",
      "action": null
    },
    "mode": "explicit",
    "interactive": false
  },
  "execution": "POST /api/v1/tools/merge-csv/run",
  "api": {
    "id": "merge-csv",
    "name": "Merge CSV",
    "category": "spreadsheet-tools",
    "description": "Append with header alignment.",
    "notes": "",
    "human_path": "/en/spreadsheet-tools/merge-csv/",
    "method": "POST",
    "endpoint": "/api/v1/tools/merge-csv/run",
    "schema_url": "/api/v1/tools/merge-csv",
    "input_schema": {
      "type": "object",
      "additionalProperties": false,
      "properties": {
        "input": {
          "type": "string",
          "maxLength": 1000000,
          "default": "",
          "description": "Plain text input. File tools use files instead unless otherwise documented."
        },
        "options": {
          "type": "object",
          "additionalProperties": false,
          "properties": {
            "delimiter": {
              "type": "string",
              "description": "CSV separator",
              "default": ",",
              "enum": [
                ",",
                ";",
                "\t"
              ]
            }
          }
        },
        "files": {
          "type": "array",
          "maxItems": 20,
          "items": {
            "type": "object",
            "required": [
              "name",
              "base64"
            ],
            "additionalProperties": false,
            "properties": {
              "name": {
                "type": "string",
                "maxLength": 200,
                "description": "Filename only, no path."
              },
              "mime": {
                "type": "string",
                "maxLength": 150
              },
              "bytes": {
                "type": "integer",
                "minimum": 0,
                "description": "Optional decoded byte count; must match content if supplied."
              },
              "base64": {
                "type": "string",
                "contentEncoding": "base64",
                "description": "File bytes as padded base64. Use the tool-specific limits.files_bytes value for the total decoded input size."
              }
            }
          }
        }
      }
    },
    "output_schema": {
      "type": "object",
      "required": [
        "tool",
        "result"
      ],
      "properties": {
        "tool": {
          "type": "string"
        },
        "result": {
          "type": "object",
          "required": [
            "text",
            "files"
          ],
          "properties": {
            "text": {
              "type": [
                "string",
                "null"
              ]
            },
            "data": {
              "description": "Parsed JSON when the textual result is JSON."
            },
            "name": {
              "type": "string"
            },
            "mime": {
              "type": "string"
            },
            "files": {
              "type": "array",
              "items": {
                "type": "object",
                "required": [
                  "name",
                  "mime",
                  "bytes",
                  "base64"
                ],
                "properties": {
                  "name": {
                    "type": "string"
                  },
                  "mime": {
                    "type": "string"
                  },
                  "bytes": {
                    "type": "integer"
                  },
                  "base64": {
                    "type": "string",
                    "contentEncoding": "base64"
                  }
                }
              }
            }
          }
        }
      }
    },
    "processing": "Server; same transformation code as browser tools",
    "limits": {
      "request_bytes": 8388608,
      "input_characters": 1000000,
      "files_bytes": 5242880,
      "max_files": 20,
      "timeout_seconds": 12
    }
  },
  "agent_processing": "Server; same transformation code as browser tools",
  "browser_agent": {
    "supported": true,
    "name": "run_current_tool",
    "discovery": "WebMCP on the human page in a supporting browser",
    "verification": "See audit/API-AUDIT.md; availability is not verification"
  }
}
```

## Page guide

Append with header alignment.

## Useful next steps

- [Compare CSV](https://happytails.ai/en/spreadsheet-tools/compare-csv/): Keyed row diff versus position diff. ([Markdown](https://happytails.ai/en/spreadsheet-tools/compare-csv.md))

- [CSV join](https://happytails.ai/en/spreadsheet-tools/csv-join/): Inner/left/full joins on explicit keys. ([Markdown](https://happytails.ai/en/spreadsheet-tools/csv-join.md))

- [CSV pivot](https://happytails.ai/en/spreadsheet-tools/csv-pivot/): Row/column groups, counts/sums, blank handling and export. ([Markdown](https://happytails.ai/en/spreadsheet-tools/csv-pivot.md))

## How to use Merge CSV

1. Choose one or more files in a supported format.
2. Review the settings, then choose Run Merge CSV.
3. Review the result, then use Copy result or a download link when available.

## Working with merge csv

Spreadsheet tasks involve values, formulas, data types and presentation. A conversion may preserve the displayed value without preserving the formula that produced it. Identifiers, dates and locale-specific decimal separators deserve special attention.

## Common questions

### Why do identifiers lose leading zeros?

A spreadsheet can interpret a text identifier as a number. Once 00123 is treated as 123, formatting may be needed to display zeros again. Preserve the original value as text when its exact representation matters.

### Does CSV keep formulas and multiple sheets?

CSV represents one flat table. It does not retain a workbook’s sheets, formatting or full formula behavior. Treat it as an exchange format for values and review how the receiving application interprets them.

Continue your workflow: [Compare CSV](https://happytails.ai/en/spreadsheet-tools/compare-csv/), [CSV join](https://happytails.ai/en/spreadsheet-tools/csv-join/), [CSV pivot](https://happytails.ai/en/spreadsheet-tools/csv-pivot/).