chainsaw

Trace the transitive import weight of any TypeScript or Python entry point. Point it at a file, get back what gets pulled in at startup and how much code it costs.

$ chainsaw trace src/cli/main.ts

src/cli/main.ts
Static transitive weight: 17.7 MB (1870 modules)
Dynamic-only weight: 16 KB (16 modules, not loaded at startup)

Heavy dependencies (static):
  highlight.js                        1.4 MB  193 files
    -> src/cli/main.ts -> ... -> cli-highlight -> highlight.js
  zod                                 537 KB  76 files
    -> src/cli/main.ts -> src/config/config.ts -> src/config/schema.ts -> zod

Modules (sorted by exclusive weight):
  src/cli/main.ts                                            17.7 MB
  src/commands/doctor.ts                                     17.7 MB
  src/config/sessions/transcript.ts                          17.5 MB
  ...

Only static imports count toward the weight. Dynamic import() and type-only imports are tracked separately.

Install

Requires Rust 1.85+:

cargo install chainsaw-cli

Usage

Python

Works the same way. Resolution matches importlib behavior -- source roots, virtualenv, .pth files, sys.path modifications, C extensions.

$ chainsaw trace manage.py

manage.py
Static transitive weight: 2.1 MB (608 modules)

Heavy dependencies (static):
  botocore                            1.2 MB  340 files
    -> manage.py -> ... -> boto3 -> botocore

Why is this package in my tree?

$ chainsaw trace src/cli/main.ts --chain zod

3 chains to "zod" (3 hops):

  1. src/cli/main.ts -> src/config/config.ts -> src/config/schema.ts -> zod
  2. src/cli/main.ts -> src/config/migrate.ts -> src/config/schema.ts -> zod
  3. src/cli/main.ts -> src/config/validation.ts -> src/config/schema.ts -> zod

Where to cut

All three chains pass through src/config/schema.ts. Chainsaw finds that:

$ chainsaw trace src/cli/main.ts --cut zod

1 cut point to sever all 3 chains to "zod":

  src/config/schema.ts                                    (breaks 3/3 chains)

Make that import dynamic and zod drops out of your startup path.

When no single file can break all chains:

No single cut point can sever all 3 chains to "chalk".
Each chain takes a different path — multiple fixes needed.

Diff

Compare two entry points:

$ chainsaw trace src/cli.ts --diff src/server.ts

Diff: src/cli.ts vs src/server.ts

  src/cli.ts                               793 KB
  src/server.ts                            3.8 MB
  Delta                                    +3.1 MB

Only in src/cli.ts:
  - degit                                42 KB
  - smol-toml                            28 KB
Only in src/server.ts:
  + undici                              1.1 MB
  + workerd                             800 KB
  + zod                                 537 KB
Shared: 21 packages

Or save a snapshot and compare before/after:

$ chainsaw trace src/cli/main.ts --save before.json
# ... make changes ...
$ chainsaw trace src/cli/main.ts --diff-from before.json

The diff subcommand compares two saved snapshots directly: chainsaw diff before.json after.json

In a monorepo, the diff target can be in a different package -- chainsaw builds a separate graph from that package's root automatically.

CI gating

$ chainsaw trace src/index.ts --max-weight 5MB --quiet --top 0 --top-modules 0

error: static weight 36.3 MB exceeds threshold 5.0 MB

Exits non-zero when static weight exceeds the threshold. Accepts 5MB, 500KB, 100B.

JSON

$ chainsaw trace src/index.ts --json --quiet | jq .static_weight_bytes

Shell completions

chainsaw completions zsh > ~/.zfunc/_chainsaw
chainsaw completions bash > /etc/bash_completion.d/chainsaw
chainsaw completions fish > ~/.config/fish/completions/chainsaw.fish

Run chainsaw --help for the full flag reference.

License

MIT

chainsaw-cli 0.1.0