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

Annotations already indicate non-read-only, idempotent, and non-destructive behavior. The description adds genuinely useful behavioral context beyond these hints: the app runs in a locked sandbox with no outbound network access, data is accessed through the sandbox bridge, and re-uploading the same version replaces it in place.

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 each carry useful information: purpose and constraints, runtime/security model, and recommended usage context. The description is front-loaded with the primary action and contains 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 tool with no output schema and only basic annotations, the description covers the core operational context: what can be uploaded, size limits, sandbox behavior, replacement semantics, and when to use it. It does not mention the response shape or any special permission requirements, which is a minor gap.

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 baseline is 3. The description adds value beyond the schema by defining the content parameter as a self-contained entry document with size and binary restrictions, and by clarifying version replacement semantics.

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 opens with a specific action on a specific resource: 'Upload or replace the code of an app YOU own'. It then adds concrete constraints (self-contained HTML/JavaScript, max 512 KB, no binary), which clearly differentiates this from generic upload or app-related tools.

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 states when to use the tool: 'ship a new build of an app you created with create_app, or to fix one after a user reports something.' It does not explicitly contrast with close siblings like write_app_artifact or update_app_manifest, so the exclusion logic is only partially explicit.

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