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

Annotations already establish that the operation is not read-only and not destructive, so the description does not need to restate that. The description adds some behavioral context ('add as a new target language') but does not disclose details like idempotency or failure behavior; this is acceptable for a simple mutation.

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 compact and front-loaded with the core action, then adds the workflow prerequisite and a clear user-facing rule. Every sentence earns its place with no redundant content.

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?

The tool has only two required parameters, both fully documented in the schema, and an output schema exists. The description supplies the prerequisite workflow and display convention, so an agent has everything needed to call the tool correctly.

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 schema covers both parameters at 100%, so the baseline is 3. The description adds extra practical semantics by instructing the agent to resolve languageId through list_languages first and by establishing the convention that UUIDs are for tool calls only and never shown to the user.

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 states a specific verb ('Add'), the exact resource ('a catalog language as a new target language'), and the target ('an existing project'). It clearly distinguishes the operation from siblings like remove_project_language and list_languages.

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 explicitly tells the agent to resolve the catalog language id first with list_languages, which is a concrete prerequisite. It does not spell out when to avoid this tool in favor of a sibling, but the context is otherwise clear.

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