CaptureKit Go SDK

The official Go SDK for the CaptureKit screenshot API.

Capture websites as PNG, JPEG, WebP or PDF, extract their content, or analyse them with AI.

The SDK exposes 7 typed methods, one per documented endpoint, plus a generic Request(). It has no dependencies outside the standard library.

Requirements

• Go 1.22 or newer

Installation

go get github.com/capturekitdev/capturekit-go

Get your API key

Sign up for CaptureKit or sign in, then copy your API key from the dashboard. NewClient("", nil) reads the CAPTUREKIT_API_KEY environment variable.

Quick start

package main

import (
	"context"
	"fmt"
	"log"

	"github.com/capturekitdev/capturekit-go"
)

func main() {
	client, err := capturekit.NewClient("", nil) // reads CAPTUREKIT_API_KEY
	if err != nil {
		log.Fatal(err)
	}
	ctx := context.Background()
	response, err := client.Content(ctx, &capturekit.ContentParams{URL: "https://example.com"})
	if err != nil {
		log.Fatal(err)
	}
	data, err := response.Map()
	if err != nil {
		log.Fatal(err)
	}
	fmt.Println(data)
}

Parameter structs mirror the API reference. Required fields are plain values; optional fields are pointers — use capturekit.String, capturekit.Float, capturekit.Int and capturekit.Bool.

Decode into your own types with response.Decode(&value).

Binary responses

Endpoints that return a file (image, PDF…) give you the bytes in Body; IsJSON tells both cases apart:

response, err := client.Capture(ctx, &capturekit.CaptureParams{URL: "https://example.com", Format: capturekit.String("png")})
if err != nil {
	log.Fatal(err)
}
if !response.IsJSON {
	err = os.WriteFile("screenshot.png", response.Body, 0o644)
}

Async jobs

Any call accepts is_async: true (useful past the 60-second server limit): the response is then a job_id. WaitForJob polls GET /v1/jobs/{id} until a terminal status (CompletedJob, Error, NotFound, BadRequest):

submitted, err := client.Content(ctx, &capturekit.ContentParams{URL: "https://example.com", IsAsync: capturekit.Bool(true)})
if err != nil {
	log.Fatal(err)
}
var accepted struct{ JobID string `json:"job_id"` }
if err := submitted.Decode(&accepted); err != nil {
	log.Fatal(err)
}
job, err := client.WaitForJob(ctx, accepted.JobID, &capturekit.WaitForJobOptions{
	OnProgress: func(job map[string]any) { fmt.Println(job["status"], job["progress"]) },
})

GET or POST

Methods use GET when the endpoint supports it (parameters in the query string); WithMethod("POST") sends them as a JSON body.

response, err := client.Analyze(ctx, &capturekit.AnalyzeParams{URL: "test"}, capturekit.WithMethod("POST"))

Any endpoint

response, err := client.Request(ctx, "GET", "/v1/usage", nil)

Errors

response, err := client.Content(ctx, &capturekit.ContentParams{URL: "https://example.com"})
if apiError, ok := capturekit.IsAPIError(err); ok {
	log.Printf("HTTP %d: %s", apiError.StatusCode, apiError.Message)
}

Error	When
*ConfigurationError	Missing API key, invalid options or unsupported method.
*SerializationError	A required parameter is missing or a value can't be sent.
*TransportError	Network failure, timeout or cancelled context (errors.Is(err, context.DeadlineExceeded)).
*APIError	Non-2xx status (StatusCode, Message, Response).
*ResponseDecodingError	A success response could not be decoded.

Retries

Requests are retried up to 3 times after a network error, a 408, 500, 502, 503 or 504, or a rate limit — which the API returns as 401 (or 429) with a Rate limit exceeded message. Per-key quota errors (…: quota daily) are not retried, nor are 400, 402, 404 or client-side timeouts. The delay starts at 1 second and grows 1.5× per retry (capped at 30 seconds); a Retry-After header wins.

client, err := capturekit.NewClient("", &capturekit.ClientOptions{
	MaxRetries: 5,                      // negative disables retries
	RetryDelay: 500 * time.Millisecond,
})

// or for one request
response, err := client.Content(ctx, &capturekit.ContentParams{URL: "https://example.com"}, capturekit.WithMaxRetries(0))

Batch requests

capturekit.Batch runs a function per item with at most 10 calls in flight and returns one BatchResult per item, in input order. A failing item never stops the others.

inputs := []string{"https://example.com", "https://www.capturekit.dev", "https://github.com"}
results := capturekit.Batch(ctx, inputs, 5, func(ctx context.Context, value string) (*capturekit.Response, error) {
	return client.Content(ctx, &capturekit.ContentParams{URL: value})
})
for _, result := range results {
	if result.Err != nil {
		log.Printf("%s: %v", inputs[result.Index], result.Err)
		continue
	}
	fmt.Println(string(result.Value.Body))
}

Constant	Default	Description
DefaultConcurrency	10	Tasks run at the same time by batch
DefaultTimeout	120 * time.Second	Request timeout
MaxRetries	3	Retry attempts after a network error, a 408/5xx or a rate limit
RetryBackoffFactor	1.5	Exponential backoff multiplier
DefaultRetryDelay	time.Second	Delay before the first retry

Timeouts and custom HTTP clients

client, err := capturekit.NewClient("", &capturekit.ClientOptions{
	Timeout:    60 * time.Second, // default 120 s; negative disables
	HTTPClient: &http.Client{Transport: myTransport},
})

Every method also honours the deadline and cancellation of the context.Context you pass.

Endpoints

7 methods, generated from the OpenAPI document.

Method	HTTP	Description
Analyze	GET / POST /v1/analyze	AI Content API analyzes any webpage and returns AI insights summary, value proposition, features, categories, use cases, and optional conta…
Capture	GET / POST /v1/capture	Browser-like Screenshot API that captures webpages as PNG/JPEG/WebP or PDF for previews, QA, reporting, monitoring, and archiving no headle…
Content	GET / POST /v1/content	CaptureKit Content API extracts structured webpage data, metadata, links, HTML/Markdown: in one request for SEO, monitoring, indexing and a…
Jobs	GET /v1/jobs/{id}	Poll the status, progress (0–100) and result of a job started with is_async=true. Polling is free. Poll until status is terminal: Completed…
Stats	GET /v1/stats	Infrastructure health for an engine or endpoint over the last hour. Not scoped to your account or tenant. Enabled per account: HTTP 403 mea…
Usage	GET /v1/usage	Retrieve real-time usage statistics and credit balance for your CaptureKit account.
WebsiteCrawler	GET / POST /v1/website/crawler	Website Crawler API fetches raw HTML from any webpage in request mode (no rendering) for fast scraping, audits, monitoring, and link/metada…

All CaptureKit SDKs

SDK	Package	Install
Node.js	@capturekitdev/sdk	npm install @capturekitdev/sdk
Python	capturekitdev	pip install capturekitdev
Go	capturekit-go	go get github.com/capturekitdev/capturekit-go
.NET	CaptureKit	dotnet add package CaptureKit
Ruby	capturekitdev	gem install capturekitdev
PHP	capturekitdev/sdk	composer require capturekitdev/sdk
Java	capturekit-java	build from source, see its README
CLI	@capturekitdev/cli	npm install -g @capturekitdev/cli
MCP server	@capturekitdev/mcp	npx -y @capturekitdev/mcp

License

MIT — see LICENSE.