Get App Icon

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

Annotations already declare readOnlyHint, openWorldHint, idempotentHint, and destructiveHint=false. The description adds meaningful behavioral context on top: the exact 336x210 dimensions, the ECP endpoint, the base64/data URL return format, and that the app must be installed. This is more than the minimal bar, though it doesn't describe error behavior for invalid app ids.

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 concise sentences with the key facts front-loaded. The 'Read-only' phrase and the appId discovery sentence are slightly redundant with annotations and schema, but every sentence still adds useful invocation context.

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 simple 2-parameter tool with no output schema, the description supplies the return format, dimensions, endpoint, valid-id discovery, and a clear alternative for a different use case. The optional device parameter is already fully documented in the schema.

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?

Input schema coverage is 100%, so the baseline is 3. The description repeats the appId examples and the /query/apps source already present in the schema, and adds only the 'installed' qualifier. It doesn't materially extend the schema's parameter 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 uses a specific verb and resource: 'Fetch the 336x210 app icon for one installed channel' and specifies the return format (base64 / data URL). It distinguishes itself from the screenshot tool by stating that screenshot should be used for a picture of the current 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?

It explicitly says when to use this tool ('to preview a channel's branding') and names the alternative for screen captures ('use screenshot instead'). It also tells the agent how to discover valid app ids via ecp_query /query/apps, which is practical guidance for invocation.

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