measure_text

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

No annotations are provided, so the description carries the full burden, and it delivers: it clarifies this is a non-rendering measurement operation and describes the return shape (width, height, advance_width, ink extents above/below baseline). It does not state whether the canvas/sprite must exist or what font-loading failures do, but the core behavioral profile is clear.

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-loads the key distinction ('without drawing it') in the first line, then a use-case sentence, then structured Args/Returns. Slightly verbose in the bold/antialias lines but every line carries parameter meaning that the schema lacks.

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 read-only measurement tool with no annotations and no output schema, the description supplies the return fields and full parameter semantics. Minor omission: it does not reference list_text_fonts as a prerequisite step or confirm it is side-effect free, but nothing critical for correct invocation 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 description coverage is 0%, so the description must compensate, and it does for all six parameters: text, font source including list_text_fonts and file/dir paths, size semantics differing between TrueType (pixels) and bitmap (scale factor), plus letter_spacing, bold, and antialias semantics. This adds substantial meaning beyond the bare schema.

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 (measure) and resource (text) with explicit scope: 'without drawing it.' This distinguishes it cleanly from the sibling draw_text, which is the obvious alternative an agent might otherwise pick.

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 concrete use case ('size a panel or centre a label in one shot instead of guessing and re-rendering') which clearly implies when to use it. It does not name draw_text as the contrasting alternative, so it stops short of explicit alternative routing.

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