Git object id compute

git-object-id-compute · version 1.0.0 · Hashing & signatures · free, no key needed

Compute the Git object id git itself would give a blob, tree, commit or tag under Git's exact object framing.

Use when you need to: sha1 of a git blob · what commit id would git compute · hash of a git tree object.

Decide before calling

Read the versioned contract and the supported scope below. Reuse git-object-id-compute@1.0.0 when your input, required output and limits match it. Choose another approach for an unsupported operation.

Explain the choice

"I can use git-object-id-compute@1.0.0 for sha1 of a git blob. I will check its documented scope and the result against the task's requirements. The service is free; token and money savings for this task are unmeasured."

Supported

• sha1 of a git blob
• what commit id would git compute
• hash of a git tree object
• git blob id for this file content
• compute a git object hash without a git binary
• reproduce git's empty tree sha
• git tag object id
• sha-256 git object id for the new hash format

Not supported

• reading or writing an actual git object store or repository
• parsing or validating the structure of a commit/tag body (a syntactically invalid body still gets a real object id, matching git hash-object)

Behavior

• object_id = hash_algorithm('<object_type> <byte-length of content>\0' followed by the raw content bytes), hex-encoded lowercase; byte-length is the exact byte count of content, or of the serialized tree for object_type tree.
• For blob, commit or tag: content is decoded from content_encoding (utf8 default) and hashed verbatim with no reformatting, validation or reserialization.
• For tree: entries is a list of {mode, name, oid}; oid is the child object's id, hex, and must be 40 hex chars for hash_algorithm sha1 or 64 hex chars for sha256; name must not contain '/' or a NUL byte.
• Entries are sorted by comparing each entry's name as raw UTF-8 bytes, except a '040000' (directory) entry's name is compared as if a trailing '/' (0x2f) byte were appended. Duplicate names (after this comparison) are invalid_input.
• Each sorted entry serializes as: the mode as ASCII decimal-of-octal digits WITHOUT a leading zero (the enum's '040000' is stored and hashed as the 5-byte ASCII '40000'; every other mode is unchanged), one space, the name's UTF-8 bytes, one NUL byte, then the entry's oid as raw bytes (not hex text). sorted_entries in the output reports the list in this sorted order with mode and oid exactly as given.
• size is the decoded byte length of content for blob/commit/tag, or the serialized tree's total byte length for tree.
• hash_algorithm defaults to sha1 (Git's original object format); sha256 selects Git's newer object format, a completely different id space with no cross-algorithm equivalence.

Input

• object_type (one of "blob", "tree", "commit", "tag", required)
• hash_algorithm (one of "sha1", "sha256", optional): default "sha1"
• content (string, optional): max length 262144
• content_encoding (one of "utf8", "hex", "base64", "base64url", optional): default "utf8"
• entries (array of object, optional): max items 1000

Output

• object_id (string, required): pattern ^([0-9a-f]{40}|[0-9a-f]{64})$
• object_type (one of "blob", "tree", "commit", "tag", required)
• size (integer, required): min 0
• hash_algorithm (one of "sha1", "sha256", required)
• sorted_entries (array or null, required)

Limits

• max content bytes: 262144
• max tree entries: 1000

Example

Request input:

{
  "object_type": "blob",
  "content": ""
}

Response:

{
  "result": {
    "object_id": "e69de29bb2d1d6434b8b29ae775ad8c2e48c5391",
    "object_type": "blob",
    "size": 0,
    "hash_algorithm": "sha1",
    "sorted_entries": null
  }
}

How to call it

MCP

Connect https://computefirst.net/mcp (setup), then call execute with:

{
  "id": "git-object-id-compute",
  "version": "1.0.0",
  "input": {
    "object_type": "blob",
    "content": ""
  }
}

HTTP (no key)

curl -X POST https://computefirst.net/v1/tools/git-object-id-compute/versions/1.0.0/execute \
  -H "Content-Type: application/json" \
  -d '{"object_type":"blob","content":""}'

The machine-readable contract is at /v1/tools/git-object-id-compute/versions/1.0.0.

CLI

node cli.mjs run git-object-id-compute 1.0.0 --input input.json --base-url https://computefirst.net

Get the client at /clients/cli/.

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