upsert_thread_field

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

With no annotations provided, the description carries the full burden of behavioral disclosure. It states the tool will 'set or update,' but lacks details on side effects, required permissions, idempotency, or error handling. For a write operation, this is insufficient for an agent to understand the full impact of invocation.

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 extremely concise—two sentences that front-load the purpose and provide immediate context. Every word serves a purpose with no redundancy.

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 absence of an output schema and annotations, the description provides adequate but not complete context. It explains the basic operation and key format, but omits return values, error conditions, and any constraints. For a mutating tool, more detail would improve completeness.

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 coverage is 100%, so baseline is 3. The description adds minor value by noting 'Field keys use Plain's snake_case format,' but the schema already covers auto-detection of type and override behavior. The description does not significantly enhance understanding beyond the 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 clearly states the tool's purpose: 'Set or update a custom field value on a thread.' It specifies the verb (set/update) and resource (custom field on a thread), and gives usage examples. However, it does not explicitly distinguish from the sibling tool 'update_thread_fields,' which might handle multiple fields, leaving some ambiguity.

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 context on when to use the tool: 'Use this to write investigation results back to the ticket.' This implies usage for single field updates. However, it does not mention when not to use it, nor does it reference alternatives like 'update_thread_fields' for batch operations, making the guidance implicit rather than explicit.

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