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

Annotations declare non-readOnly, idempotent, non-destructive, closed-world, and the description meaningfully enriches them by spelling out the upsert semantics: re-adding an existing diagram replaces the passed fields while it 'keeps its place'. That explains the idempotentHint and clarifies that nothing is destroyed or reordered, which the annotations alone don't convey.

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 sentences, zero filler. The primary action is front-loaded and the second sentence handles the duplicate/upsert edge case rather than padding the first.

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 4-param mutation with no output schema, the description covers the essential behavior including the re-add edge case. Minor gaps remain — existence requirements for collectionId/diagramId and any failure behavior — but annotations already carry the safety profile, so this is close to sufficient.

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 50% (note and scenario are documented; diagramId and collectionId are bare strings). The description restates scenario/note intent and adds useful update semantics ('the fields you pass replace its old ones'), but it does not compensate for the undocumented identifiers or explain their format.

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: appends one saved diagram to the end of a collection, with a scenario name and note. The scope ('one saved diagram', 'end of a collection') is precise enough to separate it from siblings like save_diagram and save_collection, though it never names them explicitly.

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 implied by 'add one saved diagram to the end of a collection' — an agent can infer this is the tool for populating a collection. However, there is no guidance on when to prefer this over save_diagram or save_collection, no stated prerequisites (must the diagram/collection already exist?), and no exclusions.

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