browser_run_step

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

With no annotations, the description carries the behavioral burden and does a solid job: it discloses the return payload (ok/error, duration, failure evidence screenshot), variable interpolation behavior, and the leaf-only step restriction. It does not mention side effects on the browser page or prerequisites like an already-open page, but core behavioral traits are covered.

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 tightly packed sentences with no filler: purpose and examples first, then return behavior, then interpolation and exclusion. Every sentence earns its place and the most important routing 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 tool with nested objects, three parameters, and no output schema, the description covers the essential call semantics: what steps are accepted, what happens on success/failure, and how vars are applied. The only minor gap is the unspecified format/location of the evidence screenshot, but overall the agent has enough to invoke 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 coverage is 100%, so the baseline is 3, but the description adds value by explaining the step object with action examples and clarifying how vars interpolate {{name}} placeholders before execution. This goes beyond the schema's field descriptions.

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: it runs a YATT leaf step in the current page, with concrete examples of supported actions (click, type, hover, assert_*, goto, wait_visible). It also explicitly distinguishes itself from structure-step execution handled by test_run.

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 gives clear usage context by defining what kind of steps belong here and explicitly saying structure steps (if/repeat/for_each/run_flow) should go to test_run instead. It does not enumerate all alternative tools, but the primary routing decision is handled.

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