Inspect and compare environments

Use the inspection endpoints to answer a specific question before accepting a proposed environment.

Question	Endpoint	Contacts channels	Runs a solve
Is the input locally well formed?	/preflight	no	no
Which simple pin change makes this request feasible?	/repair	yes	yes
Which packages change between two inputs?	/diff	when needed	when needed
Why is this package present?	/explain	when needed	when needed
Which specs and channels does this file declare?	/parse	no	no

Set the server URL before following the examples:

export CONDA_PRESTO_URL=http://127.0.0.1:8000

Check an input locally

Run preflight before spending time on channel access and solving:

curl --fail --silent --show-error \
  "$CONDA_PRESTO_URL/preflight" \
  --json '{
    "specs": ["python=3.13", "python=3.13"],
    "channels": ["conda-forge"]
  }' \
  | jq

An ok value of true means that no error-severity finding was produced. It does not mean that the request is satisfiable.

Preflight also accepts raw environment files:

curl --fail --silent --show-error \
  --data-binary @environment.yml \
  --header 'Content-Type: application/yaml' \
  "$CONDA_PRESTO_URL/preflight?filename=environment.yml" \
  | jq

Ask for bounded repair suggestions

Submit an infeasible inline request to /repair:

curl --fail --silent --show-error \
  "$CONDA_PRESTO_URL/repair?max_suggestions=3&max_attempts=10" \
  --json '{
    "specs": ["python==3.13", "scipy==1.5"],
    "channels": ["conda-forge"],
    "platforms": ["linux-64"]
  }' \
  | tee repair.json \
  | jq

Review a returned change before applying it:

jq '.suggestions[].changes' repair.json

Each suggestion changes one spec and has already solved on every requested platform. The endpoint never modifies the source file. completion_reason reports whether every candidate was tried or a configured limit stopped the search.

Repair accepts inline specs only. It does not parse files or propose channel changes.

Compare two proposed environments

Pass a from input, a to input, and the platforms to compare:

curl --fail --silent --show-error \
  "$CONDA_PRESTO_URL/diff" \
  --json '{
    "from": {"specs": ["python=3.12"], "channels": ["conda-forge"]},
    "to": {"specs": ["python=3.13"], "channels": ["conda-forge"]},
    "platforms": ["linux-64"]
  }' \
  | jq '.diff["linux-64"]'

Use specs or environment files for /diff. HTTP lockfile uploads are rejected when comparison would require package-record materialization. The parser still inspects their format and platform metadata without fetching package URLs.

Explain one selected package

Choose exactly one platform and name the package to trace:

curl --fail --silent --show-error \
  "$CONDA_PRESTO_URL/explain" \
  --json '{
    "package": "libzlib",
    "specs": ["python"],
    "channels": ["conda-forge"],
    "platforms": ["linux-64"]
  }' \
  | jq '.chains'

Each chain starts at a requested spec and ends at the selected package. complete: false means the bounded local graph could not account for every edge.

Extract specs and channels without solving

Use /parse when a client needs conda’s environment-specifier plugins but not the preflight findings:

curl --fail --silent --show-error \
  "$CONDA_PRESTO_URL/parse" \
  --json "$(jq -n --rawfile file environment.yml \
    '{file: $file, filename: "environment.yml"}')" \
  | jq

See HTTP API reference for response fields, status codes, and request limits.