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

Annotations supply destructiveHint=true, so the mutation risk is declared, but the description adds no behavioral context despite that — notably whether unspecified custom fields are preserved or cleared, whether values are validated against field type definitions, or what comes back. For a destructive write the merge-vs-replace semantics are the single most important undisclosed trait.

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?

Two tightly packed sentences: the operation and key format lead, and the raw endpoint follows as supplementary detail. No filler or repetition of schema 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?

With no output schema and only a destructiveHint annotation, the description should cover the gaps that remain — replacement semantics, error cases for invalid field ids, and whether staff must have permissions. It covers the id-sourcing gap well but leaves these behavioral gaps for a nested-object mutation 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?

Schema description coverage is 100%, so the baseline is 3, and the description adds value beyond it by naming the id source tool for the t-cf-<id> keys, which the schema's regex pattern alone does not reveal. It still doesn't restate per-type value formats (already in the schema), so it stops short of a 5.

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 and resource ('Set ticket custom-field values') and pins the key format ('t-cf-<id>'), which cleanly separates this tool from siblings like happyfox_update_ticket_tags or happyfox_create_ticket. An agent can identify the operation without opening the schema.

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?

It gives one useful prerequisite pointer ('ids from happyfox_list_ticket_custom_fields'), which tells the agent where to source keys, but there is no explicit when-to-use versus when-not guidance and no mention of the ticket needing to exist or which staff role may perform the change. Usage is only implied.

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