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

Annotations already declare readOnly=false, idempotent=true and destructive=false, and the description adds real value on top: it discloses the optimistic-concurrency contract via expectedUpdatedAt and reassures that no message is dispatched. It omits what happens when expectedUpdatedAt is stale (presumably a conflict error) and whether any field other than text can change.

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 short sentences with the action, the edit context, the key parameter contract, and the safety reassurance front-loaded in that order. No sentence is redundant or padded.

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?

An output schema exists, so return values need not be described. For a simple three-parameter mutation the definition covers purpose, concurrency control, and side-effect safety; only conflict/failure behavior and permission requirements are left implicit.

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 0%, so the description must carry the burden. It does explain expectedUpdatedAt meaningfully ('the draft's updatedAt'), which the schema's bare date-time format does not, but draftId and text get no added semantics beyond their self-evident names and length bounds.

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 ('Change the text of an unsent direct-message reply draft') and scopes it to text only, which separates it from create_dm_reply_draft and send_dm_reply_draft without naming them. It never explicitly names a sibling, so it falls short of a 5.

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?

'after the writer asks for edits' gives a clear triggering context, and 'Nothing is sent' rules out the send path. It does not explicitly route to alternatives such as create_dm_reply_draft or update_reader_reply_draft, so there is no explicit when-not guidance.

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