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

With readOnlyHint=true already declaring the safety profile, the description adds genuine non-obvious behavior: messages are validated ('they are checked'), rendered with Mlola components on capable hosts, and the fallback returns the check report instead of a surface. It also discloses the interaction loop where a button press returns the A2UI action in the next user message.

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?

Front-loaded with the purpose before prerequisites and fallback details, and every sentence carries information about behavior. The paragraph runs long and grafts several clauses onto one another, but there is 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 single-parameter tool with no output schema, the description covers what the agent needs: input source and prerequisite, validation, rendering path, interaction-after-render behavior, and the degraded-host return. Nothing material about calling it correctly is missing.

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; the description adds value by specifying where valid values come from (the Mlola Render catalog, via get_render_catalog) and that inputs are validated before drawing. It does not restate the message-type structure, which the schema already carries.

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 concrete verb+resource ('Shows an interface in the conversation') and disambiguates with examples (form, status card, table of results). It also positions itself against the sibling get_render_catalog by naming it as a prerequisite, so the agent can place it without opening 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?

Gives a clear prerequisite ('read get_render_catalog first') and describes the usage context, including the no-MCP-Apps host case. It does not explicitly state when to prefer check_render/check_markup over this tool, so the alternative-routing guidance is incomplete.

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