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

With no annotations the description carries the full burden, and it does substantial work: it discloses replace semantics for instructions, partial-update semantics for other fields, and an important safety consequence — runs initiated from an agent's own turn will ask before sending or posting. That last clause is genuine behavioral context an agent would otherwise miss.

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?

Roughly three dense sentences with the mutation contract and matching rules front-loaded, no filler. The final clause about agent-turn approval is a bit compressed and slightly awkward but earns its place as distinct behavioral information.

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?

No output schema, no annotations, five parameters including a nested schedule object, yet the description covers mutation semantics, identifier resolution, and a non-obvious side effect. The only omission is explicit clarification of the agent scoping parameter.

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 only 20%, so the description must compensate, and it does for the critical routine argument (id, full name, or unique partial name, with agent-scoped narrowing) and for instructions (replace, not merge). The agent parameter is only implicitly covered via 'agent narrows it,' which is a minor gap.

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: 'Change one of the user's routines,' and names the updatable fields (instructions, schedule, name). It also routes discovery through the sibling list_routines, so the agent can tell it apart from create/delete/pause variants.

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 states the partial-update contract explicitly ('Only what you give changes') and gives matching rules for the required routine argument so the agent knows how to obtain a valid reference. It does not explicitly distinguish when to use this versus pause_routine or delete_routine, which holds it below a 5.

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