Screen MCP

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

No annotations are provided, so the description carries the full burden. It discloses that the tool returns a base64 chunk and mentions concatenation, but doesn't cover critical behavioral aspects: it doesn't specify if this is a read-only operation, what permissions are needed, error handling (e.g., invalid indices), rate limits, or how chunk_base64 is structured. The description adds some context (chunk indexing and concatenation) but leaves significant gaps for a tool with no annotation coverage.

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?

The description is highly concise and front-loaded: the first sentence states the core purpose, and the second adds essential usage details. Every sentence earns its place by providing critical information without redundancy. It's appropriately sized for a tool with two parameters and clear functionality.

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?

Given the tool's moderate complexity (fetching data chunks), no annotations, and an output schema (which likely covers return values), the description is reasonably complete. It explains the chunk-fetching process and indexing, but lacks details on error cases, authentication, or how total_chunks is determined. The output schema reduces the need to explain return values, but some behavioral context is still 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 description coverage is 0%, so the schema provides no parameter descriptions. The description adds meaning by explaining that chunk_index ranges from 0 to total_chunks-1, which clarifies its purpose and constraints. However, it doesn't describe capture_id (e.g., what it is, how to obtain it) or provide format details for either parameter. The description compensates partially but not fully for the low schema coverage.

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 clearly states the tool's purpose: 'Return one base64 chunk for a screenshot session' specifies the verb (return), resource (base64 chunk), and context (screenshot session). It distinguishes from siblings like get_screenshot_manifest (which likely returns metadata) and capture_screenshot (which initiates capture), but doesn't explicitly differentiate from get_timeline_chunk (a similar chunk-fetching tool for timelines).

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 implies usage by stating 'Fetch chunks from `chunk_index=0` to `total_chunks-1`', suggesting it should be used iteratively across a range. However, it doesn't explicitly state when to use this tool versus alternatives like get_screenshot_manifest (which might provide total_chunks info) or how it relates to capture/release operations. The guidance is practical but lacks explicit exclusions or named alternatives.

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