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

Annotations already declare read-only, idempotent, and non-destructive behavior, and the description adds valuable context: it never reads or rewrites existing source, and the sole existing-file edit is returned as a line to add rather than a file to overwrite. The 'PAID' flag also discloses a cost dimension not present in annotations.

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 sentences with no filler: the first identifies the action and outputs, the second explains the manifest mechanism, and the third clarifies the non-destructive edit behavior. The key constraints are 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?

Even without an output schema, the description tells the agent what the tool produces: a screen file, a route, a registration line, and navigation instructions. It also explains the read-only edit model, so an agent has enough context 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 schema already documents all four parameters, including the tab/root distinction and the compositionId meaning. The description does not add parameter-level detail beyond what the schema provides, so the baseline 3 applies.

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: it adds one new screen to an already-exported app, and enumerates the concrete deliverables: screen file, route, registration line, and navigation. The 'already exported' qualifier and manifest-reading behavior distinguish it from siblings like emit_screen.

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?

Gives a clear condition for use: the app must already be exported and the .opointo/files.json manifest is required. It implies this is for post-export screen additions rather than initial generation, but it does not explicitly name alternatives or state when not to use it.

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