Using Glean for Code Exploration

Glean indexes source code across the organization's connected repositories. Local tools (Grep, Glob, Read) see only the current repo; this skill is for everything else.

When to reach for this

• Finding the system — "Where does our payments code live?"
• Finding the patterns — "How do other teams handle rate limiting?"
• Finding the people — combining code authorship with employee_search reveals real owners (not just titled ones)
• Prior art before designing — see reference/plan-prep.md for the research-before-plan workflow
• Cross-repo exploration — understanding systems, mapping breadth, finding contributors across the organization

The tool you'll mostly use

This skill drives the code_search MCP tool. For full param shape, inline filter syntax, and pitfalls (quoting names, the app: filter not applying, recency caveats), read ../using-glean/reference/code-search.md. That is the canonical reference; this skill carries the workflow on top.

For this skill's own workflow patterns, see:

• reference/exploration.md — exploring an unfamiliar system across repos: what to search for, what to filter, what to present
• reference/plan-prep.md — gathering enterprise context before entering plan mode for architectural / strategic work

Vetting

Not every match is worth surfacing. Code in legacy/, deprecated/, archive/, abandoned repos, or files with extensive TODO/FIXME comments will mislead the user. Apply the criteria in ../using-glean/reference/vetting.md and prefer 3 high-quality matches over 10 unfiltered ones.

Quality test

• Is this good code to reference?
• GOOD: Clean, tested, actively maintained
• ACCEPTABLE: Works but has caveats
• POOR: Hacky, deprecated, abandoned

Recency test

• Is this code maintained?
• ACTIVE: Commits in past 3 months
• SLOWING: 3–12 months since last commit
• STALE: 12+ months — likely outdated patterns

Relevance test

• Does this actually answer the question?
• RELEVANT: Directly addresses what was asked
• RELATED: Similar but different context
• TANGENTIAL: Keyword match only

Filter out: code in /deprecated/, /old/, /legacy/ paths; abandoned repositories; prototype/experimental code; code with extensive TODO/FIXME comments. Quality over quantity — 3 good examples beat 10 mediocre ones.

Key differentiator

Local tools (grep, glob) search only the current repo. Glean searches across all repositories in the organization. This is powerful for:

• Finding examples: "How do other teams handle authentication?"
• Understanding systems: "What repos touch the billing service?"
• Finding owners: "Who's been active in the payments codebase?"

Tool selection

Output expectations

When presenting code findings:

1. Cite each file with its full URL so the user can open it directly
2. Note last-update date when a result depends on currency (active patterns vs. archaeological digs)
3. Group by repo when results span many repos — it shows the user the shape of the answer
4. Flag drift when implementations disagree across teams — don't pretend consensus exists if it doesn't

Related skills

• codebase-context — structured architecture rundown for an unfamiliar system
• similar-code — find similar implementations
• find-examples — usage examples for an internal API or library
• code-owners — maintainers and contributors
• plan-prep — the workflow described in reference/plan-prep.md