Update agent custom variables

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

The description discloses a non-obvious upstream behavior: the API replaces the entire variable list on every write, so the tool performs a read-modify-write merge that preserves unmentioned variables. This goes well beyond the annotations, explaining why the operation is idempotent and destructive in specific ways. It also clarifies that variables are names only and how prompts reference them.

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?

Three dense sentences, each adding distinct value: the action, the critical read-modify-write behavior, and the naming/value semantics. No filler, no repetition of schema fields, and the most important behavioral caveat is front-loaded.

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 three-parameter update tool with no output schema, the description covers the key behavioral details needed to invoke it correctly: the merge behavior, preservation of unspecified variables, and the meaning of custom variables. It does not describe return values or error conditions, but those are less critical given the annotations and schema coverage.

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 already documents all parameters with useful descriptions, including the 'already-present names are ignored' behavior. The tool description adds meaning by explaining that variables are names only, values are supplied elsewhere, and prompts reference them via @{{variable_name}}. This enhances an agent's understanding of add and remove beyond the raw 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?

The description opens with a specific verb and resource: 'Add or remove custom variable names on an agent.' This clearly identifies the action and target, and differentiates the tool from siblings like update_agent_prompt or attach_knowledge_base. The scope (agent custom variables) is immediately unambiguous.

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 makes the operational context clear: use this tool to manage an agent's custom variable names. However, it does not explicitly say when to choose this over alternatives or when not to use it, such as when updating prompts or knowledge bases. Usage is implied rather than stated.

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