diff --git a/.prettierignore b/.prettierignore
index 9b587954a..d442ca2d1 100644
--- a/.prettierignore
+++ b/.prettierignore
@@ -2,3 +2,4 @@ source/danger-outgoing-process-schema.json
 source/danger-incoming-process-schema.json
 source/platforms/_tests/fixtures/bbs-dsl-input.json
 source/platforms/_tests/fixtures/bbc-dsl-input.json
+CHANGELOG.md
diff --git a/CHANGELOG.md b/CHANGELOG.md
index f40d760c0..307ae0463 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -15,6 +15,7 @@
 
 <!-- Your comment below this -->
 
+- Enhancement(perf): [Github] Check if the filesystem can load files instead of always using Github API [#991](https://github.com/danger/danger-js/pull/991) [@orta]
 - Fix: [Github] Multiple Inline Comments on the same file/line should all be posted [#1176](https://github.com/danger/danger-js/pull/1176) [@Rouby]
 
 <!-- Your comment above this -->
@@ -834,7 +835,7 @@ Also, `danger pr` now accepts a `--process` arg.
 ## 3.5.0 - 3.5.1
 
 - Fixed a bug where Danger posts empty main comment when it have one or more inline comments to post [@codestergit]
-- fix bug when commiting .png files on BitBucket [@Mifi]
+- fix bug when committing .png files on BitBucket [@Mifi]
 - Adds support for inline comments for bitbucket server. [@codestergit]
 
 ## 3.4.7
diff --git a/source/platforms/git/localGetHeadSHA.ts b/source/platforms/git/localGetHeadSHA.ts
new file mode 100644
index 000000000..f17942f10
--- /dev/null
+++ b/source/platforms/git/localGetHeadSHA.ts
@@ -0,0 +1,20 @@
+import { debug } from "../../debug"
+import { exec } from "child_process"
+
+const d = debug("localGetHeadSHA")
+
+export const localGetHeadSHA = () =>
+  new Promise<string>(done => {
+    const call = `git rev-parse HEAD`
+    d(call)
+
+    exec(call, (err, stdout, _stderr) => {
+      if (err) {
+        console.error(`Could not get the git HEAD for the current path`)
+        console.error(err)
+        return
+      }
+
+      done(stdout.trim())
+    })
+  })
diff --git a/source/platforms/github/GitHubAPI.ts b/source/platforms/github/GitHubAPI.ts
index 485fcf7fe..abf30a823 100644
--- a/source/platforms/github/GitHubAPI.ts
+++ b/source/platforms/github/GitHubAPI.ts
@@ -3,6 +3,7 @@ import { debug } from "../../debug"
 import * as node_fetch from "node-fetch"
 import parse from "parse-link-header"
 import pLimit from "p-limit"
+import { existsSync, readFileSync } from "fs"
 
 import { GitHubPRDSL, GitHubIssueComment, GitHubUser } from "../../dsl/GitHubDSL"
 
@@ -10,6 +11,7 @@ import { dangerIDToString } from "../../runner/templates/githubIssueTemplate"
 import { api as fetch } from "../../api/fetch"
 import { RepoMetaData } from "../../dsl/BitBucketServerDSL"
 import { CheckOptions } from "./comms/checks/resultsToCheck"
+import { localGetHeadSHA } from "../git/localGetHeadSHA"
 
 // The Handle the API specific parts of the github
 
@@ -28,6 +30,7 @@ export class GitHubAPI {
   private readonly d = debug("GitHubAPI")
 
   private pr: GitHubPRDSL | undefined
+  private gitSha: string | undefined
 
   constructor(public readonly repoMetadata: RepoMetaData, public readonly token?: APIToken) {
     // This allows Peril to DI in a new Fetch function
@@ -75,6 +78,19 @@ export class GitHubAPI {
       ref = prJSON.head.ref
     }
 
+    // Only make the check the first time file contents are requested
+    if (!this.gitSha) {
+      this.gitSha = await localGetHeadSHA()
+    }
+
+    // See if we can short-cut the API request with a FS lookup
+    // when we're sure it's on the same setup
+    if (ref === this.gitSha) {
+      if (existsSync(path)) {
+        return readFileSync(path, "utf8")
+      }
+    }
+
     const data = await this.getFileContents(path, repoSlug, ref)
     const buffer = new Buffer(data.content, "base64")
     return buffer.toString()
diff --git a/source/platforms/github/getStringDiff.test.ts b/source/platforms/github/getStringDiff.test.ts
new file mode 100644
index 000000000..030d662c8
--- /dev/null
+++ b/source/platforms/github/getStringDiff.test.ts
@@ -0,0 +1,98 @@
+function rangesOfDifferBetweenTwoStrings(source: string, target: string) {
+  const ranges = [] as { start: number; length: number }[]
+
+  const addToIndex = (index: number) => {
+    const closestIndex = ranges[ranges.length - 1]
+    if (closestIndex) {
+      const doesAddToIndex = closestIndex.start + closestIndex.length === index - 1
+      if (doesAddToIndex) {
+        closestIndex.length = closestIndex.length + 1
+      } else {
+        ranges.push({ start: index - 1, length: 1 })
+      }
+    } else {
+      ranges.push({ start: index - 1, length: 1 })
+    }
+  }
+
+  for (let index = 0; index < source.length; index++) {
+    const srcChar = source[index]
+    const targetChar = target[index]
+    if (srcChar !== targetChar) {
+      addToIndex(index)
+    }
+  }
+
+  return ranges
+}
+
+function highlightDifferenceBetweenInStrings(source: string, target: string) {
+  const ranges = rangesOfDifferBetweenTwoStrings(source, target)
+  let emTarget = target
+  ranges.forEach((range, index) => {
+    const lhs = `\e[3m`
+    const rhs = `\e[0m`
+    const additionalOffset = index * lhs.length + index * rhs.length
+    const before = emTarget.slice(0, range.start + 1 + additionalOffset)
+    const between = emTarget.slice(
+      range.start + 1 + additionalOffset,
+      range.start + range.length + 1 + additionalOffset
+    )
+    const after = emTarget.slice(range.start + range.length + 1 + additionalOffset, emTarget.length)
+    emTarget = before + lhs + between + rhs + after
+  })
+  return emTarget
+}
+
+it("sees a difference", () => {
+  const src = "Hello world"
+  const target = "Hello w0rld"
+  expect(highlightDifferenceBetweenInStrings(src, target)).toMatchInlineSnapshot(`"Hello we[3m0e[0mrld"`)
+
+  const src2 = "Hello world"
+  const target2 = "H3llo w0rld"
+  expect(highlightDifferenceBetweenInStrings(src2, target2)).toMatchInlineSnapshot(`"He[3m3e[0mllo we[3m0e[0mrld"`)
+
+  const src3 = "Hello world ok then"
+  const target3 = "H3llo w0rld no then"
+  expect(highlightDifferenceBetweenInStrings(src3, target3)).toMatchInlineSnapshot(
+    `"He[3m3e[0mllo we[3m0e[0mrld e[3mnoe[0m then"`
+  )
+
+  //   expect(rangesOfDifferBetweenTwoStrings(src, target)).toMatchInlineSnapshot(`
+  // Array [
+  //   Object {
+  //     "length": 1,
+  //     "start": 6,
+  //   },
+  // ]
+  // `)
+
+  //   const multilineInput = `
+  // ↓
+  // (↓
+  // ····<div>↓
+  // ······text↓
+  // ····</div>↓
+  // )
+  // `
+  //   const multilineOutput = `
+  // ↓
+  // (↓
+  // ····<div>↓
+  // ········text↓
+  // ······</div>↓
+  // )`
+  //   expect(rangesOfDifferBetweenTwoStrings(multilineInput, multilineOutput)).toMatchInlineSnapshot(`
+  // Array [
+  //   Object {
+  //     "length": 8,
+  //     "start": 22,
+  //   },
+  //   Object {
+  //     "length": 10,
+  //     "start": 32,
+  //   },
+  // ]
+  // `)
+})