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

Annotations already mark the operation as non-read-only, non-destructive, and idempotent. The description adds valuable behavior beyond that: the payload replaces the old one whole, and switching layout requires type plus a matching payload. This warns the agent about an important side effect without contradicting the annotations.

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 tight sentences with no filler. The most important behavioral fact, full payload replacement, is placed early and immediately followed by the required precondition.

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 complex 9-parameter mutation with a nested payload and no output schema, the description plus schema covers the core flow: fetching current state first, replacing the payload, switching layouts, and version guarding. It is not fully complete—return behavior and sort_key semantics are not addressed—but it is strong enough for correct invocation in most cases.

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 56%, so the description needs to compensate. It does clarify payload semantics and the type/payload relationship, and 'badge or time' maps to some fields. However, it leaves sort_key, tz_offset, and occurred_at_utc semantics largely implicit, so the low coverage is not fully compensated.

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, 'Edit one timeline block', and enumerates the editable aspects: content, badge, time, or layout. This clearly separates it from siblings like add_block and get_timeline.

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 an explicit precondition: 'read it with get_timeline first', which is essential before replacing a payload. It does not explicitly name alternatives or when-not-to-use cases, but the edit-vs-add distinction is strongly implied by the wording.

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