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

Annotations only cover openWorld/idempotent/destructive; the description adds the crucial partial-failure semantics ('applied in order, valid ones kept, rejected ones returned with reasons so you can fix them'), which an agent cannot infer from structured fields. It also discloses the full return payload (diagram, computed loops, what changed, open-and-edit link) and a non-obvious constraint ('you never position anything').

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?

Front-loaded with purpose, then behavior, then the command reference - a sensible ordering for a batch-command tool. Density is high but nearly every clause carries load; the inline command enumeration is long and would read better as a list, but nothing is clearly 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 tool with nine union command variants, no schema descriptions and no output schema, the description supplies command grammar, identity rules, failure handling, design constraints and the return shape. An agent could construct a valid, well-formed call from this text alone.

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 0%, so the description carries the burden, and it largely does: it enumerates the per-op payloads for addVariable and addLink, explains that loops are computed rather than supplied, and disambiguates the tempId convention (t1, t2) from existing ids (v3, l4). It leaves updateVariable, removeVariable, updateLink, removeLink, setTitle and setContext field shapes and the 200-command cap undocumented, though those op names are self-evident.

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?

Opens with a specific verb and resource ('Create a new causal loop diagram') and immediately scopes the inputs (title, one-sentence context, command batch) and destination ('store it on a shared link'). 'New' plus the shared-link storage distinguishes it from the edit_diagram and get_diagram siblings without needing the 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?

Gives concrete authoring guidance (1-3 loops at the heart of the story, at most about 12 variables, neutral measurable names) and a mandatory workflow step ('always give that link to the person'). It stops short of explicitly naming edit_diagram as the tool for subsequent changes, so the create-vs-edit boundary is implied rather than stated.

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