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

This is the strongest section: it discloses the non-obvious two-phase behavior that the call itself 'changes nothing', that it returns a preview plus a confirmation link, and that only the merchant can execute the change. That is exactly the kind of operational context annotations (readOnlyHint=false, destructiveHint=false, idempotentHint=false) cannot convey, and it correctly signals the deferred/idempotency-sensitive nature of the operation.

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?

Four short sentences with the core behavior front-loaded, which is good. However, the second sentence about money in cents appears to be carried over from a payment-related tool and does not earn its place for a routine-scheduling schema, weakening an otherwise tight description.

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 an 8-parameter mutation-path tool with full schema coverage, no output schema, and no nested objects, the description covers the crucial non-obvious behavior (preview, confirmation link, merchant gating). It omits partial-update semantics (whether omitted fields are preserved) and the merchant-approval latency, but the essentials for correct invocation are present.

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 schema already documents hour, title, prompt, cadence, weekday, dayOfMonth, and isActive with good detail. The description adds no parameter-level meaning and the one semantic aside (money in cents) maps to no parameter, so the baseline 3 applies.

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?

States a specific verb+resource ('Change a routine') that cleanly separates it from siblings routines_create, routines_delete, and routines_list. It does not explicitly name or route away from those siblings, but the CRUD positioning is unambiguous from the verb alone.

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?

Usage is only implied through the confirmation workflow; there is no explicit statement of when to prefer routines_update over routines_create or routines_delete, nor what preconditions (e.g. an existing routine id) must hold. The 'Money is integer minor units (cents)' sentence adds no routing value since no parameter is monetary.

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