tab_selectSets a tab as the default target for later actions in the session and can optionally bring it to the front, so subsequent tools run against the intended tab.
Makes a tab the default target for subsequent tools in this session, and optionally brings it to the front.
| Name | Required | Description | Default |
|---|---|---|---|
| tabId | Yes | Tab id from tabs_list. | |
| activate | No | Also activate the tab and focus its window (default false). |
Changes observed during successful MCP inspections.
v0.1.0Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations declare readOnlyHint=false and idempotentHint=true, but they don't explain what the write actually changes; the description supplies that it mutates persistent session state (the default target) rather than page content, which is valuable context beyond the annotation flags. It also notes the optional window-focus side effect of activation. It omits what happens on an invalid or closed tabId, which keeps it from a 5.
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?
A single sentence with zero waste; the primary behavior (setting the session default target) is front-loaded and the optional behavior is correctly subordinated with 'optionally'.
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 two-parameter, fully documented, non-destructive-to-content operation with no output schema, the description covers the durable effect and the activation side effect adequately. Minor gap: no mention of failure behavior for a stale or invalid tabId, which an agent would want when reusing stored ids.
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 100%, so both parameters are already fully documented, and the description's only added mapping is 'brings it to the front' for the activate flag. Baseline 3 applies when the schema carries the parameter burden.
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?
States a specific verb and resource ('Makes a tab the default target') and captures the key scope distinction: the selection applies to subsequent tools in this session, not just this call. An agent can distinguish it from tabs_list (enumerate) and tab_open (create) without reading any schema.
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 phrase 'for subsequent tools in this session' implies the right moment to call it (before page-scoped operations on a particular tab), but there is no explicit when-not guidance or named alternative such as using tabs_list to discover ids or tab_open to create a tab first. Usage is inferred rather than directed.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.