> ## Documentation Index > Fetch the complete documentation index at: https://docs.context.dev/llms.txt > Use this file to discover all available pages before exploring further. > ## Agent Instructions > Setting up Context.dev for a user? Follow https://docs.context.dev/agent-quickstart.md. MCP clients sign in with OAuth and need no API key; application code reads CONTEXT_DEV_API_KEY. # Monitors > Watch a page, a sitemap, or a site's key pages on a schedule. Get changes by signed webhook or by polling runs and changes. A monitor captures a baseline of a target, checks the target again on a schedule, and records a change when it finds a difference that counts. Receive changes as signed webhooks, or poll runs and changes through the API. ## Pick a target | What you want to know | Target | Detection | | ------------------------------------------------------------ | -------------------------- | ---------- | | Did the visible text on a page change? | `page` | `exact` | | Did something I care about change on a page? | `page` with `instructions` | `semantic` | | Were URLs added to or removed from a sitemap? | `sitemap` | `exact` | | Did something I care about change across a site's key pages? | `extract` | `semantic` | These are the only supported pairs. Exact detection reports every text difference. Semantic detection confirms a text difference, then asks an AI judge whether it matters under your `instructions`. When you omit `change_detection`, it's inferred from the target as in the table. Extract monitors cost more per run than page and sitemap monitors. See [credits](/account/credits). ## Create a monitor This monitor watches a changelog page and reports only the changes its instructions describe. Because the target has `instructions`, detection is `semantic`. The examples read your API key from `CONTEXT_DEV_API_KEY`; the [Quickstart](/quickstart) shows how to set one up. ```typescript TypeScript theme={null} import ContextDev from "context.dev"; const client = new ContextDev({ apiKey: process.env.CONTEXT_DEV_API_KEY }); const monitor = await client.monitors.create({ name: "Changelog announcements", target: { type: "page", url: "https://example.com/changelog", instructions: "Report new features, deprecations, and breaking changes. Ignore dates and typo fixes.", include_selectors: ["main"], exclude_selectors: [".timestamp"], }, webhook: { url: "https://app.example.com/webhooks/context", retry: {} }, }); console.log(monitor.id, monitor.initial_run_id); ``` ```python Python theme={null} import os from context.dev import ContextDev client = ContextDev(api_key=os.environ["CONTEXT_DEV_API_KEY"]) monitor = client.monitors.create( name="Changelog announcements", target={ "type": "page", "url": "https://example.com/changelog", "instructions": "Report new features, deprecations, and breaking changes. Ignore dates and typo fixes.", "include_selectors": ["main"], "exclude_selectors": [".timestamp"], }, webhook={"url": "https://app.example.com/webhooks/context", "retry": {}}, ) print(monitor.id, monitor.initial_run_id) ``` ```ruby Ruby theme={null} require "cgi/core" require "context_dev" client = ContextDev::Client.new(api_key: ENV.fetch("CONTEXT_DEV_API_KEY")) monitor = client.monitors.create( name: "Changelog announcements", target: { type: "page", url: "https://example.com/changelog", instructions: "Report new features, deprecations, and breaking changes. Ignore dates and typo fixes.", include_selectors: ["main"], exclude_selectors: [".timestamp"], }, webhook: {url: "https://app.example.com/webhooks/context", retry: {}}, ) puts monitor.id, monitor.initial_run_id ``` ```go Go theme={null} package main import ( "context" "fmt" "os" contextdev "github.com/context-dot-dev/context-go-sdk/v2" "github.com/context-dot-dev/context-go-sdk/v2/option" "github.com/context-dot-dev/context-go-sdk/v2/packages/param" ) func main() { client := contextdev.NewClient(option.WithAPIKey(os.Getenv("CONTEXT_DEV_API_KEY"))) monitor, err := client.Monitors.New(context.Background(), contextdev.MonitorNewParams{ Name: "Changelog announcements", Target: contextdev.MonitorNewParamsTargetUnion{ OfPage: &contextdev.MonitorNewParamsTargetPage{ Type: "page", URL: "https://example.com/changelog", Instructions: contextdev.String("Report new features, deprecations, and breaking changes. Ignore dates and typo fixes."), IncludeSelectors: []string{"main"}, ExcludeSelectors: []string{".timestamp"}, }, }, Webhook: contextdev.MonitorNewParamsWebhook{ URL: "https://app.example.com/webhooks/context", Retry: param.Override[contextdev.RetryConfigParam](map[string]any{}), }, }) if err != nil { panic(err) } fmt.Println(monitor.ID, monitor.InitialRunID) } ``` ```php PHP theme={null} monitors->create( name: "Changelog announcements", target: [ "type" => "page", "url" => "https://example.com/changelog", "instructions" => "Report new features, deprecations, and breaking changes. Ignore dates and typo fixes.", "includeSelectors" => ["main"], "excludeSelectors" => [".timestamp"], ], webhook: ["url" => "https://app.example.com/webhooks/context", "retry" => []], ); echo $monitor->id, " ", $monitor->initialRunID, PHP_EOL; ``` ```bash cURL theme={null} curl https://api.context.dev/v1/monitors \ -H "Authorization: Bearer $CONTEXT_DEV_API_KEY" \ -H "Content-Type: application/json" \ -d '{ "name": "Changelog announcements", "target": { "type": "page", "url": "https://example.com/changelog", "instructions": "Report new features, deprecations, and breaking changes. Ignore dates and typo fixes.", "include_selectors": ["main"], "exclude_selectors": [".timestamp"] }, "webhook": { "url": "https://app.example.com/webhooks/context", "retry": {} } }' ``` The API returns `201` with the monitor and `initial_run_id` (trimmed): ```json theme={null} { "id": "mon_123", "status": "active", "change_detection": { "type": "semantic" }, "schedule": { "type": "interval", "frequency": 1, "unit": "days" }, "webhook": { "url": "https://app.example.com/webhooks/context", "secret": "whsec_…", "events": ["change.detected"], "retry": { "delays_seconds": [10, 60, 300, 1800, 7200, 21600, 57600] } }, "next_run_at": "2026-09-27T03:14:00.000Z", "initial_run_id": "run_123" } ``` Creating a monitor queues a baseline run right away. The baseline run captures the first snapshot and never reports a change; later runs compare against it. Pass `initial_run_id` to [Retrieve a monitor run](/api-reference/monitors/retrieve-run) to confirm the baseline worked. If the run couldn't be queued, `initial_run_id` is `null` and the baseline runs at the next scheduled time. Store `webhook.secret` to [verify signatures](/webhooks#verify-signatures). With no `schedule`, the monitor runs once a day; see [Schedules](/monitors/schedules). ## Access A restricted API key needs `monitors:write` to create, update, delete, or run a monitor, rotate its webhook secret, and replay its webhook deliveries. `monitors:read` covers monitors, runs, changes, limits, credit usage, and delivery history. `webhook.secret` is returned only to keys with `monitors:write`. See [API keys](/account/api-keys). ## Before you rely on alerts * The baseline run completed: `status: "completed"` and `baseline_created: true`. * `instructions` say what matters and what to ignore. * Your receiver verifies signatures and deduplicates events on `X-Context-Id`. * Failed runs send no webhook, so you check runs for failures or subscribe to `run.completed` as a heartbeat. ## Related * [Targets](/monitors/targets): page, sitemap, and extract options, detection, and updates. * [Schedules](/monitors/schedules): intervals, run now, pause, and automatic pauses. * [Runs and changes](/monitors/runs-and-changes): run statuses and change records. * [Events and alerts](/monitors/webhooks): webhook events, delivery failures, and secret rotation. * [Limits and errors](/monitors/limits-and-errors): monitor limits per plan and error codes. * [Website change digests](/use-cases/website-change-digests): an end-to-end recipe. * [Create a monitor reference](/api-reference/monitors/create)