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

The description discloses the key behavioral trait of partial update ('Only provided fields are changed'), which is not carried by annotations. Annotations already declare readOnlyHint=false, destructiveHint=false, and idempotentHint=true, so this adds useful context without contradiction. It does not cover auth or error cases, but given the annotation coverage that is acceptable.

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 short sentences, front-loaded with the verb and resource, and the second sentence adds the critical partial-update caveat without any filler. Every word earns its place.

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 11-parameter mutation tool with no output schema, the description covers the core partial-update behavior but says nothing about field dependencies (e.g., tracking_type changes requiring corresponding target fields) or error behavior. The schema descriptions cover individual parameters, but the overall context is only just adequate.

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?

With 100% schema coverage, the baseline is 3. The description adds the crucial semantics that any supplied parameter is applied while unprovided parameters remain unchanged—essential for a partial update. This is meaningful beyond the individual field descriptions.

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 specifies a clear verb ('Update') and resource ('existing habit'), and adds the semantic 'Only provided fields are changed,' distinguishing it from a full replace. It does not explicitly name sibling tools, but the title and context make the purpose unambiguous.

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?

The phrase 'existing habit' implies this is for updating already-created habits as opposed to create_habit or log_habit, but it provides no explicit guidance on when to use this tool versus alternatives or exclusions. The partial-update note gives context, but not routing.

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