Start session

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

Annotations only declare openWorldHint=false and destructiveHint=false, so the description usefully adds real behavioral context: it spins up an embedded server, opens a browser window with draw.io, streams live diagram updates, and returns a drawing guide to follow. It omits lifecycle details (does it block? how to stop the server? what if a browser can't be opened), which keeps it from a 5.

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?

Four short sentences, front-loaded with the primary action and the mode branch, and each sentence carries information. There is mild redundancy in restating the browser preview three times ('open the browser', 'opens a browser window', 'browser will show diagram updates').

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?

With no output schema, the description helpfully notes the result includes the drawing guide, and it covers the side effects of a 1-param tool. Remaining gaps are minor lifecycle questions rather than anything blocking a correct invocation.

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 100%, so the schema already documents session_id with its pattern and provenance. The description's 'or continue a saved one with session_id' restates rather than extends that meaning, making the baseline 3 appropriate.

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 states a specific verb and resource ('Start a new diagram session... and open the browser for real-time preview') and cleanly splits the two modes (new vs. continue via session_id). It does not, however, distinguish itself from plausible siblings like create_new_diagram or load_diagram, whose relationship to a 'session' an agent must infer.

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?

It gives a clear selection rule for its only parameter fork: pass session_id to continue a saved diagram, omit it to start fresh, and the schema notes where session_ids come from (list_saved_diagrams). No explicit exclusions or named alternatives are given, so it stops short of full when/when-not guidance.

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