set-keywords

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

With no annotations present, the description carries the full burden and excels. It discloses the write nature, environment dependency (APPLE_PHOTOS_MCP_ENABLE_WRITES), the union/merge semantics ensuring preservation of unmentioned keywords, metadata-only impact, asset validation, AppleScript permission requirements, and the target library context. All critical behavioral aspects are transparent.

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?

Despite its length, the description is exceptionally well-structured with clear prefixed sections ('Use when:', 'Returns:', 'Do not use when:', 'Safety:') that make scanning easy. Every sentence provides unique, essential information, and the structure front-loads the primary purpose and use cases.

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 write nature, the description covers safety, permissions, library context, validation, and return values. With an output schema present, it still explains what the returned diff means and how to revert. It is fully complete for an agent to safely and correctly invoke the tool.

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?

The input schema already has 100% description coverage for the three parameters. The description adds valuable semantics beyond the schema, such as the no-op behavior for adding existing or removing absent keywords, the rejection of overlapping add/remove, and the effect of new keyword creation. This enriches the schema's basic field 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 clearly states the tool's function: 'add and/or remove keywords (tags) on a photo'. It also distinguishes this tool from sibling tools by emphasizing the non-destructive merge semantics ('without disturbing its other keywords') and explicitly contrasting with list-keywords and query in the 'Do not use when' section.

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 provides explicit use cases ('tagging workflows, fixing a mis-tag'), explicit exclusions ('Do not use when: you want to browse keywords — use list-keywords; or find photos by keyword — use query'), and an additional constraint ('A keyword passed in both add and remove is rejected'). This fully guides an agent on when and when not to use the tool.

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