Compare Files

Compare two versions of a document and get a redline of the differences.

POST /api/v1/files/compare

cURL

curl -X POST "https://api.wordsmith.ai/api/v1/files/compare" \
  -H "Authorization: Bearer sk-ws-api1-your_api_key_here" \
  -H "Content-Type: application/json" \
  -H "Idempotency-Key: 5c2e8a71-9d3b-4f06-b1e4-7a0c6d2f9b58" \
  -d '{
    "original_file_id": "9a1d7e44-2b6c-4f08-8d3a-71c5e0b9f2a6",
    "revised_file_id": "b9edaac3-4b39-496b-8991-527a2c74dae2",
    "output_format": "docx",
    "wait": 20
  }'

Running

{
  "id": "576385fc-5367-4218-99c7-02212744be3c",
  "type": "document_action",
  "status": "running",
  "progress": {
    "stage": "compare",
    "completed": 0,
    "total": 1
  },
  "resource": {
    "type": "file",
    "id": "9a1d7e44-2b6c-4f08-8d3a-71c5e0b9f2a6"
  },
  "result": null,
  "error": null,
  "poll_after_seconds": 5,
  "created_at": "2026-10-13T11:00:00Z",
  "updated_at": "2026-10-13T11:00:01Z",
  "completed_at": null
}

Preview. This endpoint is available to organisations in the Wordsmith MCP pilot. Other organisations receive 403 mcp_not_enabled. See the preview overview.

Compares an original and a revised version of a document. The output is one new file that shows every difference as a tracked change. Each input can be a DOCX, a DOC or a PDF, and they need not share a format: a PDF or DOC is converted to DOCX before the comparison.

The action runs as an operation of type document_action: the response comes back straight away, and the work runs in the background. Wait for it with wait, a callback_url, or Get Operation. The new files land in your private space. The input files are not changed. Document actions use no credits.

Authentication

Send an API key, or an OAuth access token with both the files:write and files:read scopes. files:write lets the action create its output; files:read lets it read the inputs. A token without either gets 403 with "error": "insufficient_scope".

Headers

Idempotency-Key · string

A unique key for this request, such as a UUID, up to 255 characters. A repeat with the same key within 30 days returns 200 with the same operation and does the work once. A repeat with a different body returns 409 idempotency_key_reused.

Body parameters

original_file_id · string (uuid) · required

The earlier version. Text only in this file shows as deleted.

revised_file_id · string (uuid) · required

The later version. Text only in this file shows as inserted. It must be a different file from original_file_id.

output_format · string · default: "docx"

docx for a tracked-changes Word document, or pdf for that document rendered as a PDF with the changes marked up.

wait · integer · default: "0"

Seconds to wait for the action to finish before responding, from 0 to 20. Two short documents usually compare inside 20.

callback_url · string

A public HTTPS URL that receives a signed operation.succeeded, operation.failed or operation.cancelled event when the action finishes. API keys only: an OAuth caller waits or polls instead.

Response

Returns 202 with an operation of type document_action. Its resource is the original file. A repeat with the same Idempotency-Key returns 200 with the same operation.

When status is succeeded, result is { "action": "compare", "file_ids", "summary" }. file_ids holds one id: the redline. summary is { "insertions", "deletions", "moves" }, counting each kind of tracked change.

When status is failed, error.code says why:

error.code	When
identical_documents	The two files have the same content (the same bytes, or the same text and formatting), so there is nothing to show.
resource_not_found	An input was deleted, or your access to it removed, before the work ran.
invalid_document	An input could not be read: it is damaged, password-protected or not a valid DOCX or PDF. Retrying does not help.
action_failed	The action failed for another reason. error.retryable is true: try again.

id · string (uuid)

The operation’s id.

type · string

document_action.

status · string

queued until a worker starts the action, then running, succeeded, failed or cancelled.

progress · object | null

{ "stage", "completed", "total" }. null until the work starts.

resource · object

{ "type": "file", "id" }: the original file.

result · object | null

Set when status is succeeded.

error · object | null

{ "code", "message", "retryable" }, set when status is failed.

poll_after_seconds · integer | null

When to ask again. null once the operation has finished.

created_at · string

ISO 8601 UTC.

updated_at · string

ISO 8601 UTC.

completed_at · string | null

ISO 8601 UTC, once the operation has finished.

cURL

curl -X POST "https://api.wordsmith.ai/api/v1/files/compare" \
  -H "Authorization: Bearer sk-ws-api1-your_api_key_here" \
  -H "Content-Type: application/json" \
  -H "Idempotency-Key: 5c2e8a71-9d3b-4f06-b1e4-7a0c6d2f9b58" \
  -d '{
    "original_file_id": "9a1d7e44-2b6c-4f08-8d3a-71c5e0b9f2a6",
    "revised_file_id": "b9edaac3-4b39-496b-8991-527a2c74dae2",
    "output_format": "docx",
    "wait": 20
  }'

Running

{
  "id": "576385fc-5367-4218-99c7-02212744be3c",
  "type": "document_action",
  "status": "running",
  "progress": {
    "stage": "compare",
    "completed": 0,
    "total": 1
  },
  "resource": {
    "type": "file",
    "id": "9a1d7e44-2b6c-4f08-8d3a-71c5e0b9f2a6"
  },
  "result": null,
  "error": null,
  "poll_after_seconds": 5,
  "created_at": "2026-10-13T11:00:00Z",
  "updated_at": "2026-10-13T11:00:01Z",
  "completed_at": null
}

Errors

Status	error_code	When
400	invalid_request_body	The body is not valid JSON, has an unknown field, or a file id is missing, both ids are the same, or output_format is not docx or pdf.
400	unsupported_file_type	A file is not a DOCX, DOC or PDF.
400	invalid_wait	wait is not from 0 to 20.
400	invalid_callback_url	callback_url is not a public HTTPS URL.
400	callback_signing_unavailable	The API key has no webhook secret to sign the callback with. Create a new API key, or long-poll the operation instead.
400	bad_request	callback_url was sent with an OAuth token.
403	insufficient_scope	The OAuth token lacks files:write or files:read.
403	forbidden	Your user may not upload files, so the output has nowhere to go.
404	resource_not_found	A file does not exist, or you cannot read it.
409	scan_in_progress	A file’s malware scan has not finished. Retry in a few seconds.
409	idempotency_key_reused	The Idempotency-Key was used within 30 days with a different request.