Android Navigation 3 Guide

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

Annotations already declare readOnly, idempotent, non-destructive, and closed-world, so safety is covered. The description adds genuine behavioral context beyond that: an ordering constraint (invoke before writing code) and a versioning rule (N3 is current, don't emit N2 code). It does not describe the shape of returned content, which keeps it short of 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?

Three short clauses, front-loaded with the resource identity followed by the action constraint, then the topic index. No filler sentences and nothing that could be trimmed without losing meaning.

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 zero-required-parameter read tool with no output schema and full schema coverage, the description covers purpose, timing, and available topics adequately. It could note what the returned content looks like (e.g., reference docs vs. code samples), but nothing essential is missing.

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% and both parameters are documented there, so the baseline is 3. The description's topic list duplicates the schema's topic enumeration and adds no syntax or selection guidance beyond it.

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 resource ('Navigation 3 reference') with an explicit version scoping cue ('current official library'), which cleanly distinguishes it from Navigation 2 material and from siblings like android_official_search. An agent immediately knows this returns N3 reference content.

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 an explicit trigger ('Call before any navigation code') and an explicit prohibition ('do not generate Navigation 2 NavController/NavHost for new projects'), which is stronger guidance than most sibling tools provide. Alternatives aren't named, but the when/when-not conditions are unambiguous.

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