session_type

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already establish readOnlyHint=false, idempotentHint=false, and destructiveHint=false. The description adds useful behavioral context: it fires keyboard events, returns {typed} with the character count, and is slower than session_fill. It does not fully describe side effects of triggering real keystrokes, but with annotations present the additional information is solid.

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?

Three focused sentences: primary behavior, when to use versus session_fill, and return/performance notes. Everything earns its place and the most important scoping information is front-loaded.

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 relatively simple tool with 4 parameters, no output schema, and a clear sibling relationship, the description covers what the tool does, when to use it, what it returns, and its performance tradeoff. No critical information seems missing for an agent to call it correctly.

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 the input schema already documents selector, text, ref, and tabId. The description reinforces that text is typed one character at a time and mentions the {typed} return value, but it does not need to compensate for missing schema details, so the baseline score of 3 is appropriate.

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 states a specific verb and resource: 'Type text one character at a time, firing the key events a real keyboard would.' It clearly distinguishes itself from session_fill by naming it, so an agent can tell which tool to use without inspecting schemas.

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 explicitly says to use this tool instead of session_fill when a field only reacts to keystrokes, and gives concrete examples: search boxes with live suggestions, autocompletes, and per-character validation. It also tells the agent to prefer session_fill unless this tool is needed, providing clear routing guidance.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.