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

Beyond the annotations, the description discloses the root cause of failure (bitmap font files loaded from a filesystem that this endpoint lacks), which is exactly the behavioral context an agent needs to avoid a doomed call. It does not say what actually happens if invoked anyway (error vs. no-op), leaving a small gap.

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 critical constraint is front-loaded in the first clause, followed by two alternatives, with no filler. The GitHub release URL and Claude Desktop instructions are somewhat operational detail an agent cannot act on directly, but they are short and support the hand-off to the user.

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 six-parameter mutation tool that cannot execute here, the description gives enough to make the right call: skip it and route elsewhere. The only missing piece is the exact runtime behavior when invoked despite the warning, which is minor given the tool's unusable state.

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 100%, including the path source, opacity range, output-link lifetime, extension-driven format, and overwrite semantics, so the schema carries the parameter burden. The description adds no parameter meaning of its own; baseline 3 applies.

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 never states plainly that the tool draws a text watermark onto an image and writes a new file; that comes only from the name and title. It does convey the mechanism ('the watermark is drawn with bitmap font files loaded from a filesystem') and, more importantly, that the operation cannot run on this hosted endpoint. The agent learns the capability exists but is unavailable here, which is useful but not a clean purpose statement.

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?

Strong on routing: it explicitly tells the agent not to expect this tool to work on the hosted endpoint and offers two concrete alternatives (run a local install, or upload an already-watermarked image). It does not point at any sibling tool, but no sibling performs watermarking, so the external alternatives are the correct ones.

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