Simulate pressing and holding a keyboard key in browser automation, keeping it active until explicitly released. Target specific pages or sessions for precise input control.
Hold a keyboard key down until nex_browser_key_up is called.
| Name | Required | Description | Default |
|---|---|---|---|
| key | Yes | ||
| pageId | No | Stable page ID; defaults to the session active page | |
| sessionId | No | Optional session ID; defaults to this MCP client active session |
Changes observed during successful MCP inspections.
v2026.8.14Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations provided, the description carries the full burden of behavioral disclosure. It does convey the core stateful behavior: the key remains down until key_up is invoked. However, it lacks additional context such as whether the key repeat is enabled, how modifier keys are handled, or what happens if key_up is not called. This is minimal but not misleading.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
The description is a single, clear sentence with no redundant wording. It immediately states the action and the end condition, making it easy to parse. Every word contributes to understanding.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
For a simple stateful tool with three parameters and no output schema, the description is mostly complete. It explains the hold-until-release behavior and names the release tool. However, it omits any details about key naming conventions and potential errors, which would be useful for the agent, but given the simplicity, it remains adequate.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema description coverage is 67%, meaning pageId and sessionId are documented in the schema, but the required 'key' parameter has no description. The tool description adds no information about what key values are accepted (e.g., 'A', 'Shift', 'ArrowUp'). Since the description does not compensate for the missing key semantics, the score stays at the baseline.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description clearly states the tool's action: holding a keyboard key down. It explicitly links to the counterpart nex_browser_key_up, distinguishing it from press_key or type, which involve different key interactions. The verb 'hold' and the resource 'keyboard key' make the purpose unambiguous.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
The description clearly implies when to use this tool: to press and hold a key until later released. It also references the complementary tool (nex_browser_key_up) that must be called to release the key, providing essential usage context. However, it does not explicitly mention alternatives like press_key for quick presses or when not to use this tool.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.