Browser4 is an AI-native browser engine that lets autonomous agents and people control real browsers, extract information from web pages, and automate tasks at scale. It combines browser interaction through a Rust CLI and MCP with deterministic selectors, machine-learning clustering, and language-model extraction. The catalogue entries provide skills and instructions for using Browser4.
Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx agentmods add skills/platonai/browser4/form-fillingnpx skills add platonai/Browser4 --skill form-fillinggit clone --depth 1 https://github.com/platonai/Browser4Wrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/platonai/browser4/form-filling)<a href="https://agentmods.dev/skills/platonai/browser4/form-filling"><img src="https://agentmods.dev/badge/skills/platonai/browser4/form-filling.svg" alt="Measured on agentmods" height="20"></a>What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00036 | $0.00841 |
| Opus 5 | $0.00018 | $0.00420 |
| Sonnet 5 | $0.00007 | $0.00168 |
| Haiku 4.5 | $0.00004 | $0.00084 |
Grade A, and why
form-filling scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 6d ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
How it starts
The opening of the file, as written. The whole thing — 132 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Form Filling Skill
Description
Automatically fill web forms with provided data. This skill handles various form field types and can optionally submit the form after filling.
Dependencies
web-scraping- Required for detecting form fields and structure
Parameters
| Parameter | Type | Required | Default | Description |
|---|---|---|---|---|
| url | String | Yes | - | The URL of the page containing the form |
| formData | Map<String, String> | Yes | - | Key-value pairs representing field names and values |
| submit | Boolean | No | false | Whether to submit the form after filling |
Return Value
Returns a SkillResult with the following data structure:
{
"url": "string",
"filledFields": ["field1", "field2"],
"submitted": boolean,
"message": "status message"
}
Usage Examples
Basic Form Filling
val result = registry.execute(
skillId = "form-filling",
context = context,
params = mapOf(
"url" to "https://example.com/contact",
"formData" to mapOf(
"name" to "John Doe",
"email" to "[email protected]",
"message" to "Hello!"
)
)
)
Form Filling with Submission
val result = registry.execute(
skillId = "form-filling",
context = context,
params = mapOf(
"url" to "https://example.com/signup",
"formData" to mapOf(
"username" to "johndoe",
"password" to "securepass123",
"email" to "[email protected]"
),
"submit" to true
)
)
Tool Call Specification
ToolSpec(
domain = "skill.form",
method = "fill",
arguments = [
"url: String",
"formData: Map<String, String>",
"submit: Boolean = false"
],
returnType = "SkillResult",
description = "Fill a web form with the provided data"
)
Error Handling
The skill returns a failure result in the following cases:
- Missing required parameter
url - Missing required parameter
formData - Empty
formDatamap - Form fields not found on the page
What ships with it
4 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 6d ago First seen · 132 lines · 36 tokens per session scan A 1f1b5b8a6d93
form-filling is a skill published in the GitHub repository platonai/Browser4 (1,122 stars, last pushed today), licensed Apache-2.0. It adds 36 tokens to every session and 841 once invoked, about $0.0002 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.
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