Chisel — Test Impact Analysis for Agents

The binary is chisel, built from src/ with cargo build --release. chisel-mcp is the same binary and starts stdio MCP. Oracle JSON is in tests/fixtures/oracle. Do not pip-install a package to get this binary.

Storage is the snapshot .chisel/store. chisel migrate copies test results from an old chisel.db. Other commands do not open it.

Core loop

chisel --json analyze .
chisel --json diff-impact
chisel --json suggest-tests src/calc.py
chisel --json triage
chisel --json update
chisel run -- pytest tests/

Prefer MCP when chisel-mcp is connected (26 tools). The server speaks newline-delimited JSON and also Content-Length. HTTP chisel serve is GET /health, GET /tools, and POST /call only. It is not an MCP URL and it has no /mcp path.

Always pass --json on the CLI and branch on status before treating a payload as a list. no_data, stale_db, and no_changes exit 0. error and git_error exit 1.

Status values

auto_update runs inline only when at most 50 files changed and no job is running. Otherwise the tool still returns and sets auto_update_skip_reason to too_many_changed_files or background_job_running.

Flags that change results

• working_tree true re-reads the worktree. Leave it false to use the snapshot.
• suggest_tests requires file_path. impact requires files. A missing required argument is status: "error", not an empty list.
• CHISEL_PROJECT_DIR and CHISEL_STORAGE_DIR apply when the CLI flags are absent.
• CHISEL_INCLUDE_IGNORED=1 scans ignored files. Non-git projects are unfiltered.
• Shards: CHISEL_SHARDS or .chisel/shards.toml. One snapshot per shard. Unscoped reads aggregate. Unknown shard is status: "error". Cross-shard test edges are overlaid from the parent snapshot. flakiness_trend is set when dated results span two of the last four weeks.
• Function churn and blame come from one batched git log -p stream; only files it cannot replay (dirty, untracked, diff-driver attributes) spawn git log -L or git blame.
• Above 2000 code files, file-level churn still runs and per-function churn does not (unit_churn_skipped).
• A no-op update sets edge_rebuild_skipped true and reads no history.
• risk_map/triage rows omit zero and empty fields. A refused lock returns the holder's purpose and expiry.
• chisel run records pytest and Jest and forwards the test process exit code. One snapshot flush for the whole run.
• chisel watch polls git status and runs update when the worktree changes. --interval is seconds. --once exits after one check.
• A custom parser is an executable named by CHISEL_EXTRACTOR, or by .chisel/extensions.toml when the process starts with --allow-repo-extractor or CHISEL_ALLOW_REPO_EXTRACTOR=1. CHISEL_DEP_EXTRACTOR or dep_extractor in that file supplies test dependencies. A tool argument cannot turn the repo file on. The path must stay inside the project. Its libraries stay outside this binary.
• stats returns counts. It does not embed every historical result.
• List tools apply a default limit and set truncated when the cap cuts the list.
• Suggestion source is one of direct, co_change, import_graph, static_require, hybrid, fallback, working_tree.
• Locks are advisory rows in the snapshot.

When a repo is large

start_job with kind analyze or update returns queued and a real job_id before the work finishes. Poll job_status. cancel_job is observed between files. Do not wait on a synchronous analyze of a monorepo inside an MCP timeout.