Extract a rectangular region from a TUI screen buffer by setting row and column bounds, enabling precise output checks in buffer mode.
Extract a rectangular screen region — buffer mode only.
| Name | Required | Description | Default |
|---|---|---|---|
| col_end | No | ||
| row_end | Yes | ||
| col_start | No | ||
| row_start | Yes | ||
| session_id | No | default |
| Name | Required | Description | Default |
|---|---|---|---|
| text | Yes | ||
| error | Yes | ||
| success | Yes | ||
| session_id | Yes |
Changes observed during successful MCP inspections.
v0.3.0Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the full behavioral burden. 'Buffer mode only' is a genuinely useful operational constraint, but there is no disclosure of the coordinate origin, indexing base, behaviour of the open-ended col_end, error conditions, or session semantics. The rest of the safety and behavior profile is left to inference.
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?
A single front-loaded sentence with no filler or repetition. It is efficient, though its brevity shades into under-specification rather than active concision.
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?
An output schema exists, so return values need not be explained, but with 5 parameters at 0% schema coverage and no annotations, the definition leaves the agent without coordinate conventions, mode limitations, or session behavior. For a region-extraction tool where off-by-one and mode errors are easy, this is too thin.
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% across 5 parameters, so the description must compensate and does not. It never clarifies whether row/col indices are 0-based, whether row_end/col_end are inclusive or exclusive, or what a null col_end (the default) means — precisely the ambiguities that would cause a mis-call.
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 ('extract') and resource ('rectangular screen region'), which naturally distinguishes it from siblings like capture_screen (whole screen) and get_line (single line). It does not explicitly name those siblings, but the scope of the operation is clear from the description alone.
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 only guidance is the constraint 'buffer mode only', which tells the agent this won't work in some other (unspecified) mode but never says when to prefer this over capture_screen, get_line, or get_cursor_position, nor what to use instead in non-buffer modes. No conditions, prerequisites, or alternatives are given.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.