Check the screen

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

Beyond readOnlyHint=true, the description discloses real behavioral traits: it blocks/polls for up to 5 seconds, and passing checks get promoted to assertions while recording. That is non-obvious context an agent would not infer from the schema. It does not say what happens on timeout/failure (exception vs. returned false), which is the one meaningful gap.

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 short sentences, front-loaded with the core assertion, then the 5-second wait bound, then the recording caveat. No restatement of the title ("Check the screen") and no filler.

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 zero-required-parameter, no-output-schema read tool with a readOnlyHint already declared, this covers purpose, timing tolerance, and test-recording effects. The remaining ambiguity — failure semantics and whether text and id can be supplied together — is minor but real.

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 would be 3, but the description adds genuine semantics the schema lacks: it explains what visible=false means (assert absence rather than presence), which the schema only marks as "Default true." It also frames id and text as interchangeable targets. The checked and serial parameters are left entirely to the schema.

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?

Specific verb-plus-resource: "Check that text (or an element id) is on screen, or with visible false that it is not." An agent immediately knows this is a screen-state assertion rather than a UI action like phone_tap or phone_type. It stops short of naming the nearest sibling (phone_look) or stating any exclusion, so 4 rather than 5.

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?

Usage is implied by the phrasing: use it to verify on-screen state, and pass visible=false to verify absence. The recording-mode sentence hints at when this is especially valuable (during test recording), but no explicit when-to-use, when-not-to-use, or alternative (e.g. phone_look vs phone_assert) is offered.

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