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feat: Add ability to inject script to run on page load #568

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78127e2
Add initScript capability
gernberg Nov 17, 2025
86e0bb2
Add tests
gernberg Nov 17, 2025
45a9c2b
Update description of parameter
gernberg Nov 17, 2025
8b7de1a
Update formatting
gernberg Nov 17, 2025
dbc2109
Automatic doc update
gernberg Nov 17, 2025
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1 change: 1 addition & 0 deletions docs/tool-reference.md
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Original file line number Diff line number Diff line change
Expand Up @@ -149,6 +149,7 @@
**Parameters:**

- **ignoreCache** (boolean) _(optional)_: Whether to ignore cache on reload.
- **initScript** (string) _(optional)_: (optional) A JavaScript function to be executed by the tool on new document for every page load before any other scripts.
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@OrKoN OrKoN Nov 17, 2025

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thanks for the PR! I have asked a few details on the issue. Do you think the new_page tool could be a better place for the init script? Any thoughts how to remove a previously specified init script and if removing it is needed? For your use case, could it be better to pass an init script for all pages via a CLI argument or do you want the LLM to generate the init script?

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@gernberg gernberg Nov 24, 2025

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Haven't thought that much about the different approaches to be honest.
I would be fine to just close this PR for now as it's very minimal (it's just a snapshot basically of what I'm playing with locally at the moment) and keep the discussions in the issues for now to land on a good / better general solution for the problem I'm trying to solve :)

- **timeout** (integer) _(optional)_: Maximum wait time in milliseconds. If set to 0, the default timeout will be used.
- **type** (enum: "url", "back", "forward", "reload") _(optional)_: Navigate the page by URL, back or forward in history, or reload.
- **url** (string) _(optional)_: Target URL (only type=url)
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10 changes: 10 additions & 0 deletions src/tools/pages.ts
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Expand Up @@ -116,6 +116,12 @@ export const navigatePage = defineTool({
.boolean()
.optional()
.describe('Whether to ignore cache on reload.'),
initScript: zod
.string()
.optional()
.describe(
'(optional) A JavaScript function to be executed by the tool on new document for every page load before any other scripts.',
),
...timeoutSchema,
},
handler: async (request, response, context) => {
Expand All @@ -132,6 +138,10 @@ export const navigatePage = defineTool({
request.params.type = 'url';
}

if (request.params.initScript) {
await page.evaluateOnNewDocument(request.params.initScript);
}

await context.waitForEventsAfterAction(async () => {
switch (request.params.type) {
case 'url':
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22 changes: 22 additions & 0 deletions tests/tools/pages.test.ts
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Expand Up @@ -193,6 +193,28 @@ describe('pages', () => {
assert.ok(response.includePages);
});
});
it('navigates to correct page with initScript', async () => {
await withBrowser(async (response, context) => {
await navigatePage.handler(
{
params: {
url: 'data:text/html,<div>Hello MCP</div>',
initScript: 'window.initScript = "completed"',
},
},
response,
context,
);
const page = context.getSelectedPage();

// wait for up to 1s for the global variable to set by the initScript to exist
await page.waitForFunction("window.initScript==='completed'", {
timeout: 1000,
});

assert.ok(response.includePages);
});
});
});
describe('resize', () => {
it('create a page', async () => {
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