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

Annotations only declare readOnlyHint=false; the description goes well beyond by stating the operation is a chained write, that old and new keys swap atomically 'at the same instant', and warning it 'changes stored state and is not safe to repeat blindly'. It also documents the exact message both keys sign.

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?

Three front-loaded sentences that each carry weight: purpose, mechanics/signing, and the disambiguation plus write warning. The embedded message template is dense but functional rather than padding.

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 mutating tool with minimal annotations and no output schema, the description covers the write behavior, atomic swap, and signing details that the schema alone leaves implicit. It doesn't address failure modes such as the clock-skew rejection or the role of the `secret` parameter, leaving minor gaps.

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 already 83% (baseline 3), but the description adds real meaning by defining the composite signed message that ties old_thumbprint, new_thumbprint, and signed_at together, clarifying what old_signature and new_signature must cover.

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 and resource ('Rotate from one of your active bound keys to a new one') and explicitly distinguishes itself from the `rotate` sibling. An agent can tell it apart from rotate, revoke_key, and signing_bytes without opening a 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?

Names the competing alternative and the condition that separates them ('Not the same as `rotate`, which replaces your bearer secret'). Strong disambiguation, but it doesn't spell out prerequisites such as needing an already-bound active key beyond the implicit 'one of your active bound keys'.

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